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THE LIBRARY
OF
THE UNIVERSITY
OF CAU^ORNIA
LOSAI JELES
£3-'^j ♦is
\-
/
THE
INDIA DIRECTORY,
^C. 4'C.
/
THE
INDIA DIRECTORY,
OB,
DIRECTIONS FOR SAILING
TO AND FROM THE
EAST INDIES,
CHINA, AUSTRALIA, AND THE INTERJACENT PORTS
OF
AFRICA AND SOUTH AMERICA:
COMPILED CHIEFLY FROM
ORIGINAL JOURNALS OF THE HONOURABLE COMPANY'S SHIPS,
AND FROM
OBSERVATIONS AND REMARKS,
EESULTIXG FROJI THE EXPERIENCE OF TWENTY-ONE YEARS IN THE NAVIGATION OF THOSE SEAS.
BY
JAMES HORSBURGH, F.R.S. R.A.S. R.G.S.
CORRESPONDING MEMBER OF THE IMPERIAL ACADEMY OF SCIENCES, ST. PETERSBUHGH ; AND OF THE ROYAL SOCIETY OF NORTHERN ANTIQUARIES, COPENHAGEN; HYDROGRAPHER TO THE HONOURABLE EAST INDIA COMPANY.
They that go down to the sea in ships, that do business in great waters ; these see the norks of the Lord, and his wonders in the deep. — Psalm cvii. v. 23, 24.
VOLUME FIRST.
FIFTH EDITION.
LONDON:
Wm. H. ALLEN AND CO.,
BoofeStrUrS to tijc S^onourablf rtjc dBaiUintiia Company, 7, LEADENHALL STREET.
1841.
C?ntcrfti at *tationcr$' m^ll
Printed by J. L. Cox & Sons, 75, Great Queen Street, Lincnhi's-Inii FieUis.
/HI
TO THE
HONOURABLE THE COURT OF DIRECTORS
EAST INDIA COMPANY,
The Fifth Edition of the late Captain Horsburgh's Sailing Directions is respectfully inscribed, in grateful remembrance of their distinguished patron- age of the Author's labours to promote the safety of navigation, by
HIS FAMILY.
London, June, 1841.
O ^ A '2
11GB115
PREFACE TO THE FIFTH EDITION.
The long acknowledged value of the late Captain Horsbiiigh's East India Direc- tory, while it has afforded to the Editor a powerful motive for using his best eflbrts to maintain undiminished its just reputation, has at the same time rendered it unne- cessary for him to offer any thing more by way of preface, than a brief notice of those points iu which this Fifth Edition will be found to differ from the preceding editions.
The general plan of the work has of course been sedulously preserved ; but where any alteration in the mere arrangement of the details seemed likely to promise either greater perspicuity in the directions, or increased facility of reference, it has been deemed advisable to adopt it. These alterations will chiefly appear in the division and order of a few of the chapters,— in the more careful restriction of each subject to its respective division, — and in the addition of a running title at the head of each page. It has also been thought that it would be useful to the mariner to make all the bearings Magnetic; for although the system adopted in the former editions, of employing tlie compass for winds and courses, and the true rhumbs for bearings and currents, might have had its advantages, yet this distinction might not be always remembered in the hurried consultation of the book in moments of anxiety and danger.
Captain Horsburgh's Introduction remains unaltered, except in that part of it relating to the subject of Local Attraction, wiiich in this edition the Editor has en- deavoured to adapt to the present more advanced state of the science of Magnetism, and to illustrate by the introduction of some easy rules, now commonly employed by seamen.
It is also necessary to state that the Editor has availed himself of much important information, which would assuredly have been adopted by the candid and vigilant
PREFACE TO THE FIFTH EDITION.
author had his life been spared. For instance — the positions on the Coast of Brazil have been corrected from the surveys of Baron Roussin, Captain Fitz-Roy, and others. Those of the Canary Islands and the Western Coast of Africa, from the Admiralty surveys recently completed by Captain Vidal. A slight change has also been made in the longitudes of the Eastern Coast of Africa, as it appears that Captain Owen, whose authority is every where cited by Captain Horsburgh, had assumed the longitude of the Cape of Good Hope five minutes less than that which has been subsequently established at the Royal Observatory of that place.
Elaborate directions for the navigation of the Red Sea, by Captains Moresby and Elwon, of the Indian Navy, lately published by the Honourable East India Company, have, by the liberal permission of the Court of Directors, been transferred to this work verbatim ; and much additional information on the coast of Arabia, the Persian Gulf, the River Indus, and the Maldiva Islands, has been added from the admirable surveys conducted under their autliority by the officers of the Indian Navy.
A minute description of the South- West and South coasts of Ceylon, by Mr. Twynam, the Master Attendant at Point de Galle, has also been inserted ; as well as several contributions to the hydrography of the West and North-west Coasts of Aus- tralia, and of Bass's Straits, by Captain Wickhara, of H.M.S. Beagle, under whose direction the Admiralty survey of those distant regions is now proceeding.
In conclusion — the intimate knowledge of this work which the Editor has necessa- rily acquired in preparing it for the press, will perhaps exonerate him from apparent jjresumption in here adding his testimony to the just and general opinion of its great merits ; — and in expressing his conviction that the vast accumulation of facts, toge- ther with the sound and seamanlike advice and directions which it contains, cannot fail to render the India Directory an enduring monument of the unwearied industry, skilful resources, and sagacious judgment, of its celebrated author.
PREFACE TO THE FOURTH EDITION.
In submitting a Fouitli Edition of this Sailing Directory to the public, and to those Navigators who frequent the Oriental Seas and adjacent parts, the author returns his sincere thanks for their candid reception of the former editions of his work, and he trusts that the present will be found still more worthy of public confidence.
To correcting and enlarging the Second Edition with useful information, from dis- coveries made after the original publication of the India Directory, he devoted a great portion of his time ; the result of which will be perceived, by reference to the foUovving localities, the descriptions of which have either been re-written, with many important additions, or comprising original materials.
Geographical situations of the principal harbours and headlands on the Coasts of Spain and Portugal, with directions. — Canary Islands. — Coast of Guinea, and West Coast of Africa. — Chief Harbours on the Coast of Brazil, and Rio de la Plata. — Bouvet's Island. — Gough's Island. — Tristan de Acunha. — Bird Islands, and Dodding- ton Rock, and Knysna in South Africa. South Coast of Terra Australis, and Bass' Strait. — Africa, East, and North-East Coasts to the Red Sea, and Arabian Coast. — Island Mazeira. — Gulf of Persia, nearly all re- written, greatly enlarged, and cor- rected from late surveys. — Aldabra Islands, true situation ascertained. Several late discovered Shoals, and geographical limits of Saya de Malha Bank. — Maldiva Islands, their principal Channels elucidated, and lost knowledge restored, from original journals and other documents. — Directions for Marmagoa Road. Gulf of Manar. — Great and Little Basses, Ceylon. — Hooringottah River, Bengal. — Directions for Sail- ing between Malacca Strait, Bengal, and Madras ; with many other useful observa- tions and directions.
In the Third Edition, much important information was added to the preceding one, and many valuable discoveries elucidated, among which were the following.
True geographical position of Funchal. — Cape de Verde Islands, and several parts on the West Coast of Africa, from late surveys. — ^Table Bay, Cape Good Hope. — Algoa Bay, and several places on the East Coast of Africa. — North-West and
PREFACE TO THE FOURTH EDITION.
Northern Coasts of New IloUand, entirely new. Geographical position and description of tiie Islands and dangers in the Seychelle and Madagascar Seas, mostly all re-written from late explorations and surveys. — Shoals in the Red Sea. — Geographical positions of Headlands on the South Coast of Arabia. In the Persian Gulf, the Eastern Coast of Arabia described, with the correct situations of the Headlands, Towns, Islands, and Dangers adjacent, from the late laborious surveys performed by the officers of the India Navy ; the whole of this coast having been formerly unknown to European navigators.
This Fourth Edition, now submitted to the public, has been enriched with so much valuable matter, extracted from recent marine surveys, as probably to render it a Standard Work for Oriental Navigation ; for the author's constant aim has been, (luring many years of unremitted attention and researclj, to render it as perfect as possible. The whole of the Coasts of South, East, and West Africa, Madagascar, Mozambique Channel, and adjacent dangers, have been improved, from the able survey of those parts, by Captain W. F. VV. Owen, of the Royal Navy, during four years of great exertion and privation. The Coast of Persia along the East side the Gulf, the South Coast, or Coast of Mukran ; the Coasts of Scind at Kattiwar have been des- cribed from late surveys of the officers of the Indian Navy, together with those of So- cotra^nd the Red Sea, from the beautiful survey of these localities, now finished, by the same officers. The Eastern Coasts of the Bay of Bengal, and the adjacent Islands, have been improved from the correct surveys of Captain D. Ross, the Company's Marine Surveyor. The geographical positions of the Coasts of Malabar and Coro- niandel have been corrected from the Great Trigonometrical Survey of Hindoostan, The Eastern Coast of China has been described, and its navigation elucidated, together with a new chart of that coast, from a selection of manuscripts and other materials the author has obtained from Canton, or otherwise ; chiefly the result of observations made in vessels which frequent that coast, and carry on a contraband trade in opium.
With these additions, and the diligence used in precluding every species of error, the author hopes that the utility of the India Sailing Directory to British seamen may prove as great as his wishes for their safety and the nautical prosperity of this Great Maritime Empire.
CONTENTS.
|
Page |
Page |
||
|
INTRODUCTION |
i |
Velocity of the Wind |
xi |
|
Wind |
... ib. |
Waves of the Sea |
xii |
|
Trade Winds |
... ib. |
Luminous Appeai-ance of the Sea ... |
... xiii |
|
Monsoons or Periodical Winds ... |
iii |
Temperature of the Sea |
XV |
|
Variable Winds ... |
V |
Currents or Tides |
... xvi |
|
Land and Sea Breezes |
... ib. |
Magnetism ... |
... xvii |
|
Squalls |
vi |
Variation of the Compass |
... xix |
|
Storms and Hurricanes ... |
vii |
Aberration or Local Attraction |
... ib. |
|
Whirlwinds |
viii |
Chronometers |
. . . XXX |
|
Marine Barometer |
ix |
Precautionary Remarks |
. . . xxxi |
|
Change of the Moon |
xi |
Explanatory Remarks |
...xxxiii |
ENGLAND towards Madeira ; places of shelter near this route ...
From Madeira to the southward : Canaries, and Cape de Verdes
Salvages,
A Table denoting the Equatorial Limits of the Trade Winds between Africa and America experienced in every month of
the year , 22
Abstracts and Remarks on Passages to and
from St. Helena ... ... 41
Eastern Passage ... ... ... ib.
Western Passage ... ... ... 47
Comparative View of Passages ... ... 49
West Coast of Africa and adjacent Islands,
with the Winds and Currents ... ... 51
Coast and Islands ... ... ... ib.
Winds and Currents ... ... ... 56
Brazil Coast ... ... ... ... 59
Headlands and Harbours ... ... ib.
Winds and Currents ... ... ... 67
Passages of Ships ... ... ... 68
Instructions and Observations for Navigating
the Rio de la Plata, or River Plate ... 70
From the Coast of Brazil towards the Cape
of Good Hope 80
Passage across ... ... ... ... ib.
Islands near the Route ... ... ... 81
Cape of Good Hope ...
Cape and Bank of Agulhas ...
Description of the Coast and Bank Currents ...
Winds, Weather, and Doubtful Dangers, with Remarks on Ice Islands near the Bank of Agulhas Winds and Weather Doubtful Dangers Ice Islands
From the Cape of Good Plope towards Bass o crciiL .••■ ••• ••• ••• ■■•
Islands in the Southern Ocean ... South Coast of Australia Winds and Currents a
84
97
ib. 9S
101
ib. 103 106
108
ib.
115
121
i
CONTENTS.
West and N.W. Coasts of Australia
Page 123
From St. Paul towards China by the Pas- sages East of Java, with a Description of the N.W. Coast of Australia 133
The Passage ... ... ... ... ib.
Coast and Islands ... ... ... 136
Islands to the soutliwai-d and south-eastward of Java, tlie adjacent Straits and South Coast of Java, with Directions to sail from St. Paul Island to the Strait of Sunda ... 142 Islands to the southward and south-east- ward of Java ... ... ... ... ib.
Passage from St. Paul to Sunda Strait ... 149
The Outer Passage to places on either side the
Bay of Bengal 152
Prevailing winds ... ... ... ib.
Passage to the Bay of Bengal ... ... 153
Passage to Madras ... ... ... 154
From the Cape of Good Hope towards Bom- bay, Ceylon, and Bengal ... ... 156
Passage to the eastward of Madagascar ... 159
From the Cape of Good Hope to the Islands of Bourbon, Mauritius, and Rodrigue, and from thence towards India ... ... 161
Passage to Bourbon, &c. ... ... ib.
Description of Rodrigue, Mauritius, and Bourbon ... ... ... ... ib.
Passage to India .. ... 169
East Coast of Madagascar
... 170
Islands and Dangers N. E. and North of Madagascar 178
Chagos Archipelago
... 199
Mozambique Channel 209
West and N.W. Coasts of Madagascar ... ib.
Winds and Currents 226
The Channel Passage ... ... ... 227
Comoro Islands and adjacent Dangers ... 229
From the Comoro Islands towards India ... 236
Dangers n,.
Passages of Ships, shewing Winds and
Currents ... ... ... ... ;§.
Directions ... ... ... ... 238
South Coast of Africa, from Cape Agidhas
to Algoa Bay 039
Page Coast of Africa, from Algoa Bay to Cape Corrientes ... ... 248
Coast of Africa, from Cape Corrientes to Mozambique 254
Coast of Africa, from Mozambique to the Equator 264
Coast of Africa from the Equator to Ras Jar d'Afoon, with the Island of Socotra ... 282
Coast of Africa, from Ras Jar d'Afoon to the
Straits of Bab-el-Mandeb 293
Sailing Directions for the Red Sea ... 298
Introduction ... ... ... ... ib.
Abstract of Chronometric Measurements 299 Sailing Directions from the Strait of Bab- el-Mandeb to Mocha 300
Approaching Mocha .. ... ... 301
From Jibbel Seajarn to Ras Billool ... ib. Islands and Rocks between Ras Billool
and Jibbel Zoogur 303
Islands and Rocks adjacent to Great Har-
nish Islands ... ... ... ... ib.
Islands and Rocks between Ras Billool
and Jibbel Zoogur ... ... ... 304
Coast of Yemen from Mocha to Loheia ... ib.
Zebayer Islands ... 307
Coast of Yembo from Loheia to Ras Toor-
fah 308
Coast of Arabia from Ras Toorfah to
Coorafidah ... ... .. ... 315
Coast of the Hedjaz from Coomfidah
to Leet ... 319
from Leet to Jid-
dah 323
Coast of Arabia from Jiddah to Tirahn
Island 328
Straits of Jubal and Gulf of Suez ... 335
Coast of Abyssinia from P.as Billool to
Ras Hurub and thence to Coobach ... 340 Eastern and Northern Islands on the
Dhalac Bank 344
Southern and Western Islands ... ... 347
Core Nowarah ... ... ... ... 351
Inner Channel to Suakin ... ... ... 352
Coast of Nubia from Suakin to Core
Dullow 355
Outer Reefs and Inner Channel ... ... 359
Coast of Nubia and Egypt from Core
Shenab to Shadwan Island ... ... 360
Gulfof Akabah 364
Shoals in the Centre of the Red Sea ... 365
Centre Cliannel of the Red Sea 366
Inner Channels ^— ... ... ib.
CONTENTS.
Page
Channels from the Centre to the Inner
Channels ... ... ... ... 367
Winds and Weather in Centre and Inner
Channels 368
Tides and Currents ... ... ... ib.
Winds and Currents between Suez and
Jiddah, by Capt. Moresby 369
Winds and Currents of the Red Sea, by
Commander Rogers ... ... ... 370
Signification of Words used in Directions
for the Red Sea 371
Additional Remarks on the Red Sea ... 372
Directions and Descriptions ... ... ib.
Winds and Currents 375
Passages to and from the Red Sea ... ... 376
Coast of Arabia from the entrance of the
Red Sea to Misenaat in Ion. 50° 43' E. ... 380
Coast of Arabia from Misenaat to Ras-el- Had, and thence to the Entrance of the
Persian Gulf 391
Persian Gulf 40/
Arabian side ... ... ... ... ib.
Persian side ... ... ... ... 432
Passage from the Persian Gulf to the Mala- bar Coast 453
Approaching Bombay Harbour in the S.W.
Monsoon 455
Bombay Harbour ... ... ... ... 456
Islands and Remarkable Hills ... ... ib.
Dangers, with Marks to avoid them ... 459
Tides, Soundings, Ike. ... ... ... 463
Directions for entering the Harbour ... 464 Directions for Working into the Harbour
at night... ... ... ... ... 465
Directions for Working out of the Harbour 467
Coast of India from Bombay to Surat River 468
Gulf of Cambay and Banks near the Entrance 474
Coast and Dangers ... ... ... ib.
Directions ... ... 476
Guzarat or Kattiwar Coast and the Gulf of
Cutch 478
Goapnaut Point to Dwarka ... ... ib.
Gulf of Cutch 480
Passages from India to Muscat, and to the
Entrance of the Persian Gulf 483
Page Coasts of Sinde and Persia, including the River Indus ... ... ... ... 486
South Coast of Persia from Ras Mooarree to Cape Jask ; called the Coast of Muk- ran ... ... ... ... ... 493
Western Coast of India from Bombay to Cape
Comorin ... ... ... ... ... 498
Coast of Concan ... ... ... ib.
Coast of Canara ... ... ... 506
Coast of Malabar 510
Directions to Sail from Bombay to the South- ward in the S.W. monsoon ... ... 519
Monsoons, Land and Sea Breezes and Cur- rents on the western side of Hindoostan, with General Directions ... ... ... 521
Laccadiva Islands, and the adjacent Banks, with the Nine and Eight Degree Channels 526
The Maldiva Islands 533
The Atolls and Minor Channels ... 535
Principal Channels ... ... ... 539
Minor Channels ... ... ... 541
GulfofManar ... ... ... ... Uj.
Ceylon, West Coast, from Manar to Point de Galle 546
Ceylon, South Coast, from Point de Galle to Elephant Hill ; with the Great and Little xjasses ... ... ... ... ... oo f
General Remarks on the South-west and
South Coast of Ceylon, by Mr. Twynam 569
Eastern Coast of Ceylon, from Elephant Hill to Trincomalee, with Sailing Direc- tions ... ... ... ... ... ib.
Trincomalee Harbour and Bays ... ... 573
Ceylon, North-east and North Coasts, from Trincomalee to Point Pedro 579
Palk Bay, with the Winds and Currents on
the East Coast of Ceylon 582
Palk Bay ib.
Winds and Currents ... ... ... 584
Coast of Coromandel, from Point Calymere to Madras 586
CONTENTS. Page I
Coast of Coromandel from Madras to tlie Nortliward
Coast of Golconda ... ...
Coast of Orixa ... ... ...
Entrance of the Hoogly or Calcutta River Sands, Reefs, and Islands Entrance Channels
597
599
605
613 ib. 617
Directions for approaching the Hoogly River 622
Directions for sailing from False Point to the Sand Heads and to Sagor Road ... ...
Storms in and near the Hoogly, with some account of the Tides and the Bore of that River ...
Coast of Bengal from Codgee Deep to Chit- tagong, and the interjacent Rivers
Monsoons and Currents in the Gulf of Ben- gal
Passage to Bengal, from the Southern parts of the Gulf ... ... ... ...
From Bengal to Madras and the Southern parts of the Gulf ...
From the Gulf of Bengal to Bombay or other
CQo places to the westward, during the South-
~ west Monsoon ... ... ... ...
634
Passage between Bengal or Madras and the Strait of Malacca ...
Page 637
642
648
650
654 657
INTRODUCTION.
COMi'ENDIUM OF WINDS, WAVES, TIDES, CURRENTS, MAGNETISM, VARIATION OF THE COMPASS, &c.
PARTICULAR, OR LOCAL WINDS, WEATHER, AND CURRENTS,
are described in the different parts of this work, to which the reader is referred ; yet it may, nevertheless, be expedient to give here a snmmary view of the winds in general, with some remarks on the causes which usually produce those which prevail with more or less regularity on the surface of our globe.
WIND is a current of air, or a part of our atmosphere, in a state of more or less principal rapid motion ; its principal cause is a partial or local rarefaction of the air by heat. ^"."^^ "' When the air is heated, it becomes specifically lighter, and in this state naturally ascending, the less rarefied or colder air rushing into its place to restore the equili- brium, forms a current of air, or what is properly called wind. Heat also increases evaporation, by which the atmosphere is rendered more elastic, and capable of re- taining a greater quantity of moisture in the gaseous state than it can when colder; this may be considered as another cause tending to produce diversity in winds and weather, as an addition of moisture expands in the air, and renders it specifically lighter than it would be at the same temperature with humid vapour.
Electricity must be considered as a third cause acting on the atmosphere, and having great influence in the local changes of v\inds and weather. Currentsof air are always produced by the passage of electric matter; and when the atmosphere is expanded by the presence of the electric fluid, and surcharged with aqueous vapour, it is incapable of supporting a great quantity of the latter, which consequently descends in wet fogs or rain, while the denser and more elastic air near the rainy district rushes towards it, to restore the equilibrium.
Winds may be arranged under three distinct heads; Constant, Periodicctl, and Characierof Variable. Constant Winds are those which blow always in the same direction, and are called Trade Winds. Periodical Winds, or those which blow one part of the year in one direction and the other part in a contrary one, are generally called Mon- soons. Variable Winds are those which are not subject to any determinate periods or uniformity.
TRADE WINDS seem to be occasioned by the rotatory motion of the earth on Tradt winds. its axis, combined with the influence of the sun in rarefying the atmosphere between
b
ii INTRODUCTION.
tlie tropics. The cold dense air at the poles woiikl naturally move along the surface (){ tiie "lobe to take the ])lace of the hot rarehed air at the equator; but the earth's rotatory motion, and tlie gradually increasing velocity of this motion at its surface from the poles to the ecjuator, oblige these polar currents of air to diverge from their meri- dians on their route to the equator, and ultimately to acquire a direction from East to West.
From the rotation of the earth, the sun's apparent diurnal motion is from East to West ; consequently, the points of greatest rarefaction, which are those under the sun, must move in continued succession in the same direction with that luminary. The places, therefore, of greatest rarefaction following the sun from East to West, the denser air must move towards them, and thus occasion a constant easterly wind in the ocean remote from land between the tropics.
Hence, by the dense air proceeding from the polar regions in a northerly and south- erly direction towards the equator, and afterwards more westerly towards the points of greatest rarefaction, a N.E. wind is produced on the North side, and a S.E. wind on the South side of the equator. These trade winds, both in their direction and limits, incline towards the sun or place of greatest rarefaction; that is, when the sun is near the tropic of Cancer, or returning from it, having greatly heated the northern hemi- .sphere, the S.E. trade wind inclines further from the East point than in the opposite season, and blows with strength towards the place of greatest rarefaction ; and its northern limit reaches nearly to, and in some places, beyond the equator. Tlie N.E. trade wind, at the same time, generally inclines nearer the east point than in the other season, blowing with less strength, and becoming contracted in its limits ; the southern limit then receding several degrees to the northward of the equator. And in the op- posite season, when the southern hemisphere is greatly heated by the sun, the N.E. trade wind blows stronger, inclines farther from the East point, and approaches nearer to the equator ; the strength of the S.E. trade wind, at the same time, being diminished considerably by the influence of the sun.
As there is a perjjetual current of air proceeding from the Polar regions to the equator, where it is rarefied, while the superior gravity of the cold makes the heated air ascend to the upper regions of the atmosphere, whence it returns to the poles, to preserve the equilibrium, this upper current of air must proceed from the parts in which the heat is greatest, so that by a kind of atmospherical circulation, admirably adapted to the preservation of animal life, the N.E. trade wind below will be attended by a S.W. wind above ; and the S.E. trade wind below with a N.W. wind above. This opinion is corroborated by the clouds in the upper part of the atmosphere being frequently seen to move in a direction contrary to the trade winds, and by an in- stantaneous change of wind often experienced when the limits of the trade winds are passed.
Trade winds are only constant in the ocean at a considerable distance from land ; for large islands and continents obstruct the regular currents of the atraosphei'e, and thereby produce either periodical or variable winds. When land is heated by the influence of the sun, the atmosphere over it becomes rarefied, the air acquires motion, and a wind is produced, blowing from the ocean towards the land. This may be exem- plified by the winds on the African coasts, within the limits of the N.E. trade, blowing often from North and N.W. about Cape de Verde; and from S.W. and S.S.W. betwixt the Coast of Guinea and the Cape of Good Hope, within the limits of the S.E. trade; instead of N.E. and S.E., as is experienced when well out from the land, in the open ocean.
INTRODUCTION. lU
When the land of New Holland is heated by the presence of the sun in the southern hemisphere, the wind blows generally from the westward upon the N.W. coast; from the S.VV. upon the West coast; from S.W., South, and S.E., upon the South coast; and from S.E. and eastward upon the East coast of that extensive tract of land. Winds, indeed, blow nearly always from the sea, towards the heated atmosphere over the land ; but contiguous to shores, sea and land breezes are often experienced.
High land, much more than low land, obstructs the regular progress of winds ; for a steady trade wind will pass over a considerable tract of low level land without being much changed in its direction or velocity ; particularly if that land be barren and des- titute of moisture. But if the wind come in contact with high land or mountains, it is compressed in passing over their summits; as the atmosphere being heated by the sun's rays according to its density is much warmer at the bottom than at the top of mountains; consequently the air is cooled in its ascent, and being frequently con- densed into humid clouds or fog, is discharged in wet misty vapour, or in small rain, upon the tops of the mountains. This may be often seen on the Table Mountain at the Cape of Good Hope, or on high islands between the tropics, when the sun shines bright below, with clear weather around.
The presence of the sun in either hemisphere obstructs considerably the regularity and strength of the trade wind in that hemisphere, and vice versa.
The Trade Winds extend generally to about 28° on each side of the equator. Limits of the and there is usually a considerable space between them, in which light variable r™'"^ ^^""'''■ winds prevail mostly from the westward, forming in several parts of the globe, near the equator, a kind of monsoon.
The N.E. and S.E. trade winds prevail in the open sea, in the Atlantic and Pacific Oceans, and from the great extent of the latter, they generally blow more steadily in it than in the former ; and the S.E. trade wind in the southern Atlantic Ocean blows more steadily than the N. E. trade wind to the northward of the equator, where the ocean becomes contracted between Cape de Verde and the northern extremity of the coast of Brazil ; but towards the West India Islands, the N.E. trade wind generally blows steadily between East and E.N.E.
The S.E. trade wind prevails also in the Indian Ocean, from within a few degrees of the East side of Madagascar nearly to the Coast of New Holland, between the parallels of 10° and 28° S.; but in this ocean, from lat 10° S. to the coasts of India, the winds are periodical.
MONSOONS, or PERIODICAL WINDS, are those which blow half of the Monsoon.. year from one quarter, and the other half year from the opposite direction. They blow more steadily in the East Indian Seas than in any other place, particularly to the northward of the equator, from the coast of Africa to the eastern side of the Bay of Bengal; also in the China Sea, but with somewhat less regularity in the northern part of it.
The principal cause of these winds is the situation of the land as connected with Their cause. the course of the sun ; for the extensive coasts of Arabia, Persia, India, &c., being greatly heated when the sun is vertical to them, the atmosphere becomes rarefied there, and a S.W. wind blows from the ocean towards the land to restore the equilibrium. This current of air proceeding from the ocean, being highly charged with moisture in the state of gas, is gradually condensed into rain, which descends in great quantities upon the coasts of India that front the ocean in a south-westerly direction.
b2
f
IV
INTRODUCTION.
Seasons and plact's in wli ihey prevail
S.W. Mon- soon.
ich
N.E. soon.
Mon-
N.W. Mon- soon.
S.E. Mon- soon.
Westerly winds.
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Wlieu the sun returns into the southern hemisphere, the atmosphere there becomes "•reiitlv rarelied, and, by evaporation and cold winds from the northward, the land on The Nortli side of the equator soon parts with its ..heat, and the atmosphere over it becomesden.se; a N.E. wind or monsoon is then produced in North latitude, blowing towards the heated parts about the equator. This is the dry season on the coasts of India for the wind blowing from the land brings fliir weather; and the rainy season is produced by tiie wind blowing from the ocean towards the land, which is generally the case on both sides of the tropics. • • , t ■•
Were there an extensive tract of land near the southern tropic in the Indian Ocean, probably a regular N.W. and S.E. monsoon would alternately prevail between that tropic and the equator, similar to the N.E. and S.W. monsoon, in North latitude. This we may suppose would be the case, for although the N.W. monsoon in the open sea seldom extends beyond lat. 8° or 10'' S., yet in the vicinity of the East coast of Madagascar and the N.W. coast of New Holland, that monsoon extends several degrees farther to the southward, by the land being greatly heated when the sun is near the southern tropic.
The S.W. monsoon prevails from April to October, between the equator and the tropic of Cancer, and it reaches from the East coast of Africa to the coasts of India, China, and the Philippine Islands ; its influence extends sometimes into the Pacific Ocean as far as the Marian Islands, or to about Ion. 14.5° E., and it reaches as far North as the Japan Islands. In the same season, a S.S.W. monsoon prevails to the southward of the equator in the Mozambique Channel, between the Island of Mada- o-ascar and the coast of Africa, which is occasioned by the conformation of the lands on each side of that channel.
The N.E. monsoon prevails from October to May, throughout nearly the same space as that mentioned above ; but the monsoons are subject to great obstructions from land ; and in contracted places, such as Malacca Strait, they are changed into variable winds. Their limits are not every where the same, nor do they always shift exactly at the same period.
The N.W. monsoon prevails between the N.E. part of Madagascar and the West coast of New Holland from October to April, and it is generally confined between the equator and 10° or 11° of South latitude, but subject to irregularities. This monsoon seldom blows steadily in the open sea, although in December and January it generally prevails, and in these months sometimes extends from lat. 10° or 12° S. across the equator to lat. 2° or 3° North. This is the rainy monsoon to the southward of the equator, and the S.E. monsoon is the dry season.
The S.E. monsoon predominates from April to October in the space last-mentioned, and in some places reaches the equator, when the sun is near the northern tropic; but this monsoon may be considered as an extension of the S.E. trade following the sun, and when that luminary returns to the southern tropic it recedes to lat. 10° or 12° S.
The parts where the N.W. and S.E. monsoons prevail with greatest strength and regularity are in the Java Sea, and from thence eastward to Timor, amongst the Mo- lucca and Banda Islands, and onward to New Guinea.
Westerly winds are sometimes experienced near the equator, in the Pacific Ocean, a great way to the eastward of New Guinea ; and also in the Atlantic Ocean, westerly winds at times occur near, or a little to the northward, of the equator, forming a coun- ter current to the regular N.E. and S.E. trade winds which prevail on each side of it.
INTRODUCTION. V
VARIABLE WINDS prevail in both hemispheres from lat. 28° or 30° to the Poles, VariaWe winds. but those from West and W.S.W. generally predominate in North latitudes; and those from West and W.N.W. predominate in South latitudes.
The prevalence of westerly winds in high latitudes has been thus accounted for. The upper parts of the atmosphere having a motion towards the Poles, contrary to the trade winds, and becoming condensed beyond their limits, descend to the surface of the earth or sea; thus producing the motion from the West towards the East, to restore the equili- brium which has been destroyed by the trade winds. Immediately beyond the limits of the trade winds, the westerly winds are generally found to prevail.*
These westerly winds, in high latitudes, are liable to obstructions and changes from various causes, the influence of the sun being mutable and uncertain in the Temperate Zones ; but beyond the Arctic and Antarctic Circles, where a settled frost and cold atmosphere constantly prevail, strong gales and sudden shifts of wind are not so liable to happen as at a greater distance from the Poles.
The sun's presence in either atmosphere has great influence upon the prevailing westerly winds in high latitudes; in the Northern Atlantic Ocean the wind generally inclines to W.S.W. in the summer months ; and in winter, almost constantly to W.N.W. between the coasts of Newfoundland and Ireland. In the British Channel easterly winds often prevail in February, March, April, and part of May; during the other months, westerly winds prevail greatly.
On the N.W. coast of America south-westerly winds prevail in the summer months; and northerly winds during winter.
In the southern hemisphere, during the summer months, when the sun is near the tropic of Capricorn, the winds are sometimes very variable, but prevail at West and W.N.W. In the winter months they blow mostly from W.S.W. and West, and sometimes from South or S.E. Westerly winds jjrevail off the Cape of Good Hope, Cape Horn, and Cape Van Diemen, particularly when the sun is near the tropic of Cancer; but on the western coasts which form these promontories, the wind frequently prevails from the southward, when it is blowing strong from tlie westward off their extremities. And south-easterly or southerly winds are generally found to prevail more than any other, in February, March, and part of April, in tlie vicinity of those headlands.
LAND AND SEA BREEZES may be considered as a kind of alternating winds, Land and Sea which are generally experienced in settled weather upon coasts or islands between the '"^"''*- tropics. They arise from the circumstance of land being a better conductor of heat than water, and consequently being susceptible of a higher degree of temperature by the action of the sun than the sea : this increase of temperature during the day rare- fies the incumbent atmosphere, and a current of colder air rushes in from the sea to supply the deficiency, and forms what is called a sea-breeze. The progress of this breeze is regressive upon the sea, as it commences close to the shore where the motion of the air first inclines to the land, and then gradually extends out to sea; so that
* Col. Reid, speaking of Storms in high latitudes, says, " It has been shewn that the hurricanes which originate within the trojiics, increase in diameter and diminish in force as they proceed towards the poles ; and as the meridians approach each other, the gales may become huddled together. They may, therefore, fre- quently neutralize each other and become irregular. Their force, too, may often fall off, until the strength of the wind on that side of the circle where it blows from East is unable to reverse the regular westerly atmo- spheric current, and to convert it into a temporary easterly gale ; and this may be the reason why easterly storms are less frequent in both hemispheres in the latitudes within which Great Britain is situated." — Law of Storms, p. 368.
yi INTRODUCTION,
vessels close in with the shore get the regular breeze sooner than those which are in tije offing.
After sun-set, the atmosphere over the land becomes cool by evaporation ; and at what- ever time of the night it exceeds in density that over the sea, the air takes a motion from the land towards the more rarefied parts over the sea, producing what is called the lund-breeze. This is a progressive breeze ujion the sea, as it begins on the shore, and gradually extends to seaward ; and its approach may be sometimes known by an increased noise of the surf.
These land and sea breezes extend in some places only to a small distance from the shore ; but on the Malabar Coast, in the fair season, where they prevail prohahly with greater regularity than on any other part of the globe, their influence is perceptible at the distance of "20 leagues from the land.
When the land is greatly heated, and the evaporation not sufficient to cool the at- mosphere over it below that of the adjoining sea, there will be no land breeze, and in such case the wind blows mostly from seaward; this maybe observed in the Temperate as well as in the Torrid Zone.
During summer in England, when the weather is settled and serene, a gentle breeze from the sea frequently rises and increases with the altitude of the sun ; it is strongest after noon, when the air over the land is greatly rarefied, and it declines with the setting sun. The evaporation from the land during the night being in this country not suffi- cient to cool the atmosphere over it, below that of the adjoining sea, a land breeze is consecjuently seldom experienced in the night.
The temperature of the atmosphere being nearly the same over the land and sea, calms generally prevail in the night, until the sea-breeze returns, when the atmosphere over the land becomes heated by the sun in its diurnal course.
Squalls. SQUALLS are generally of three kinds ; that called the ARCHED SQUALL is
frequently experienced, and is usually distinguished by the arched form of the clouds near the horizon, but sometimes it assumes the appearance of a dense black cloud, par- ticularly when highly charged with rain or electric matter. From the time that the arch or cloud is first seen above the horizon, its motion is sometimes very quick to the zenith, the interval being scarcely sufficient to allow a ship to reduce the necessary sail before the wind reaches her, which happens when the cloud has approached to the zenith. At other times, the motion of the cloud is very slow, and not unfrequently it disap- pears, or is dispersed, the impulse of the wind being then not sufficient to reach a ship. As a general rule, it may be observed, that if there be rain in these squalls preceding the wind, the latter will probably follow the rain in sudden severe gusts; whereas, if the wind precedes the rain, the squalls are seldom so furious, and terminate in moderate showers of rain. This general rule, however, is often interrupted by the operation of local causes. THE DESCENDING SQUALL is not so easily discerned as the former, because it issues from clouds which are formed in the lower parts of the atmo- sphere near the observer; and when clouds are thus formed, they generally produce showers of rain and successive squalls of wind.* THE WHITE SQUALL is not often experienced ; but it sometimes happens near, or within the tropics, particularly in the vicinity of mountainous land. This squall generally blows very violently for a short time, and as it is liable to happen when the weather is clear, without any appear-
* This cloud is called the Nimlus by Meteorologists, who have distinguished all the various aspects of the clouds by appropriate names ; although this classification is not yet adopted by seamen.
INTRODUCTION.
VI 1
Winds in straits or channels.
ance in the atmosphere to indicate its approach, it is consequently very dangerous. The only mark that accompanies it is the white broken water on the surface of the sea, which is torn up by the force of the wind.
Squalls, and also storms, are sometimes progressive, at other times regressive, when obstructed by an opposite wind, or according as the point of greatest rarefaction is situated, as may be seen in the description of the sea-breeze.
When a squall is opposed by an opposite wind, its motion is greatly retarded thereby, and a ship sometimes in this case outruns the squall, and overtakes other ships which are within the limits of the opposite wind.
Progressive winds, when they have an opposite wind to subdue, are frequently pre- ceded many hours by a swell, which extends a great way before them.
In straits or channels formed between high lands, strong winds generally blow directly through them; this is experienced in many parts of the eastern seas, such as the Straits of Shadwan in the Red Sea, the Mozambique Channel, Straits of Macassar and Lombock, also in the entrance of the River St. Lawrence in North America, and frequently in the Frith of Forth in Scotland, although the latter is not bounded by very high land.
In many places between the tropics, where shoal coral banks shoot up out of deep winds over water, a decrease of the prevailing wind is frequently experienced upon them ; for *''°''''*' when a steady wind is blowing over the surface of the deep water, no sooner does a ship get upon the verge of a shoal coral bank, than a sudden decrease of wind is often perceived. This is probably occasioned by the atmosphere over these banks being less rarefied, and cooler, by the increased evaporation, than that over the deep water; consequently not requiring so great a supply of air to restore the equilibrium, as the circumjacent parts which are more rarefied and heated. Water, in small quantities, parts quickly with its heat, but retains it when in large quantities ; in other words, the quantity of water evaporated and the cold generated in a given time is always in proportion to the extent of surface and the depth of the evaporating mass : the evapora- tion, therefore, over shoal banks is always greater than over deep parts of the sea, and the atmosphere, as well as the surface of the water, proportionally cooler over the former than over the latter.
STORMS may be classed under three heads; GALES OF WIND, HURRI- CANES, and WHIRLWINDS.
Storms.
GALES generally happen beyond the tropics, outside of the limits of Trade Winds; caiesof wind. for in high latitudes, gales of wind, or storms, blow sometimes from one direction several days together, particularly during winter. These strong gales prevail mostly from the westward, and they are not so liable to shift round suddenly as the storms near the tropics ; this, however, sometimes happens, and has occasioned the loss of many ships in the Atlantic Ocean, having their square sails set, and consequently not preparecl for a sudden change.
The gales of wind which happen near and within the tropics are generally of short duration, and liable to veer round suddenly to an opposite direction.
HURRICANES are seldom experienced beyond the tropics, nor nearer to the Hurricanes. equator than lat. 9° or 10° North or South : they rage with greatest fury near the tropics in the vicinity of the main land or islands ; far out in the open ocean, they rarely occur; and when they happen within 10° of the equator, they generally are less violent than nearer to the tropics.
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Viii INTRODUCTION.
' Tliese are dreadful tempests, in which the wind shifts sometimes suddenly from one direction to the opposite, raising the sea in pyramids ; its violence is frequently so 2;reat as to overcome all resistance, breaking the masts of ships, and tearing up trees by the roots. Tiie velocity of the wind in some violent hurricanes has been estimated about 80 or 90 miles an hour: in a pleasant brisk gale it is about 20 miles an hour. In some places, hurricanes are occasionally accompanied by an earthquake.
Hurricanes happen among the West India Islands, near to the East coast of Mada- gascar, near the islands of Mauritius and Bourbon, and to the eastward of these islands, within tiie limits of the S.E. trade: they are also liable to happen near the coasts of India, particularly in the Bay of Bengal at the changing of the monsoons.
They are called Ty-foongs by the Chinese, and frequently happen on and near the coasts of Ciiina, extending from thence to the eastward of Luconia, and to the north- eastward as far as the Japan Islands. A description of them will be found in Volume Second of this Work, in the First Section, under the title "China Sea:" and the hurricanes which hai)pen near the islands of Mauritius and Bourbon are described in the section where directions are given for the returning passage from India towards the Cape of Good Mope.
wi,iri«inrt» WHIULWINDS are sometimes occasioned by high uneven land: when the wind
spom"^'" '* blowing strong, gusts from the mountains descend sometimes with a spiral or whirling motion upon the surface of the contiguous sea. But the phenomenon usually known by the name of WHIRLWIND when seen upon land, and called a WATER- SPOUT when it happens at sea, is generally attributed to electrical causes; as it occurs mostly in warm climates, when black dense clouds appear low in the atmo- sphere, which, being highly charged with electric fluid, thunder or lightning is mostly experienced with a whirlwind ; and at sea, it is almost invariably accompanied by rain or hail.
Wlien a water-spout is forming at a small distance, a portion of a dense cloud is ob- served to descend and stretch itself towards the sea in a conical shape ; at the same time the surface of the sea immediately under it is agitated, and ascends a little way in the form of steam or white vapour, from the centre of which a small cone proceeding upwards unites with that projected from the cloud; the water-spout is then formed: frequently, however, the acting cause is not adequate to its completion, in which case the half-formed water-spout soon disperses.
There is in the middle of the cone that forms a water-spout a white transparent tube or column, which, when viewed at a distance, seems like a stream of water as- cending, and gives it a very threatening aspect; but when closely approached, this partly vanishes. I have passed close to several water-spouts, and through the vortex of some that were forming, and was enabled to make the following observations :
By an electrical force, or ascending whirlwind, a circular motion is given to a small part of the surface of the sea, in which the water breaks, and afterwards acquires a whirling motion with a velocity of 2, 3, to 4 or o knots. At the same time, a consider- able portion of the water in the whirlpool is separated from the surface in minute par- ticles, resembling smoke or vapour, accompanied by a hissing noise from the strength of the whirlwind; these particles continue to ascend with a spiral motion to the impend- ing cloud. In the centre of the water-spout there is a vacuum,* in which none of the small particles of water ascend ; and in this, as well as around the outer edges of the
" Probably a calm. If it were a vacuum, the water would rise and fill it."— Co/. Reid's " Law of Storms," p. 10.
INTRODUCTION. IX
water-spout, large drops of rain fall, because in those places the power of the whirl- wind is not sufficient to support the ascending particles.
The vacant space in the centre of the water-spout seems, when viewed at a distance, to be that which has a white transparent appearance, like a column of water, or a hollow glass tube. In calm weather, water-spouts are generally perpendicular, but occasionally they have an oblique or curved direction, according to the progressive motion given them by the prevailing winds. Sometimes they disperse suddenly, at other times they move rapidly along the surface of the sea, and continue a quarter of an hour or more before they disappear.
Water-spouts are seldom seen in the night ; yet I once passed near to a large one in a cloudy dark night. The danger from water-spouts is not so great as many persons apprehend, for it has been said, that when they break, a large body of water descends sufficient to sink any ship. This does not appear to be the case, for the water descends only in the form of heavy rain, where it is broken from the ascending whirlwind ; but there is danger in small vessels of being overset when carrying much sail, and large ships, if their top-sails are not clewed up and the yards secured, may be liable to have them carried up to the mast-heads by the force of the whirlwind, and thereby lose their masts. It is sometimes thought, that the firing of a gun when near a water-spout will break it, and effect a dispersion; the concussion produced in the atmosphere by the explosion destroying in such case the cohesive force of the whirlwind. In the vicinity of water-spouts, the wind is subject to fly all round in sudden gusts, rendering it pru- dent for ships to take in their square sails.
When a whirlwind happens on land, all the light substances on the surface of the earth within its course are carried up in a spiral motion by it. I have observed one pass over Canton River, in which the water ascended like a water-spout at sea, and some of the ships that were moored near its path were suddenly turned round by its influence. After passing over the river, it was observed to strip many trees of their leaves, which, with the light covering of some of the houses or sheds, it carried up a considerable way into the atmosphere.
THE MARINE BAROMETER is a very useful instrument, especially in high Marine Ba.o- latitudes, in assisting navigators to anticipate approaching storms : previous to a hard gale of wind, there is generally a great fall of the mercury, and even near the tropics the fall of it before a storm or hurricane is usually considerable. Within 9° or 10° of the equator, there seldom or never is a hurricane or storm of long duration, but whirl- winds, and hard squalls of a few hours' continuance, are sometimes experienced within these parallels, without any fall of the mercury. Indeed, the barometer is of little use as a guide in prognosticating storms which may happen within the tropics; except that before a severe hurricane there is often a considerable fall of the mercury, when the latitude is not less than 14° or 15° North or South.*
In high latitudes, the motion of the mercury in the barometer, like the winds, is
mutable and uncertain; but previous to a storm or gale of wind, there is commonly a
great fall, and the mercury begins to rise before the conclusion of the gale, sometimes
even at its commencement, as the equilibrium in the atmosphere begins to be restored.
Although the mercury sinks lowest before high winds, it frequently sinks considerably
* I have engraved an atmospherical register for facilitating the use of the Marine Barometer ; by exhibiting its monthly range in each of the 12 sheets which the register contains, with an introductory sheet by way of example : this register is constructed for a period of 3 years, and is much more convenient than the usual method of registering the height of the mercury by cyphers.
C
meter.
I
X INTRODUCTION.
before a heavy fall of rain ; and when the mercury stands low, the air is light and de- prived of expansibility or elasticity, therefore not capable of supporting much gaseous moisture; at sucli periods, consequently, rain generally falls. The mercury also sinks on the approach of thunder and lightning, or when the atmosphere is highly charged with electric matter.
In serene settled weather the mercury commonly stands high, also in clear frosty weather. The mercury, in the open sea, is in general inclined to rise with easterly, and fall with westerly winds, ft is likewise necessary to remember, that in the northern hemisphere, in the open sea, the mercury rises with northerly and falls with southerly winds ; because, the former coming from the frozen parts near the pole, are more dense than the latter, which blow from the equatorial regions. In the southern hemisphere, the contrary takes place, for there the mercury rises with the cold southerly winds and falls with northerly winds. These effects are more particularly observed in high lati- tudes in the ocean, for obstructions and irregularities will always happen near land ; because tiiere, the rarefication and expansibility of the atmosphere are not so equal as over the ocean.
After very warm and calm weather, in winter particularly, a storm is likely to follow ; or at any time that the atmosphere is greatly heated above the medium tem- perature.
It is proper to observe, that in the open ocean between the tropics, in settled wea- ther, there is ajiti.r and reflux in the atmosphere twice every 24 hours, resembling the Atmospheric tidcs of the sea ; but these atmospheric tides depend upon the sun's influence and the rotation of the earth, and do not follow the motion of the moon. The rise and fall of the mercury, in consequence of these tides, is about 6 or 7 hundredths of an inch, in settled weather, near the equator ; the high station happening about 1 1 o'clock in the morning and 11 o'clock at night, and the low station about 5 o'clock in the morning and evening. The regularity of this flux and reflux of the atmosphere is obstructed by land, but in the ocean it prevails to lat. 26° North and South ; and in fine steady wea- ther it may be perceived as far as lat. 30° or 32° North or South.* Exclusive of the change in the barometer caused by the diurnal atmospheric tides between the tropics, Sir John Herschel, in his voyage to the Cape of Good Hope in November and Decem- ber 1833, observed a permanent depression of the mercury, especially at or near the equator, below wliat exists beyond the tropics in both hemispheres, — and the quantity of this permanent depression he estimated at two-tenths of an inch.
By proper attention to the marine barometer, the experienced navigator may often be enabled to anticipate the changes of weather : and in some seas, he may by its indications even take in or let out reefs in the night. It is also advisable to observe the phases and progress of the moon, for it is reasonable to suppose the influence of that planet upon the atmosphere must be considerable, in penetrating through it to the surface of the ocean.
* An abstract of 22 months' observations with two marine barometers is recorded in the Philosophical Transactions of the Royal Society for 1805, wherein I have described more fully this flux and reflux of the at- mosphere in different parts of the globe, from actual observation.
The influence of the atmosphere upon the mercury in the barometer, may perhaps be partly attributed to the expansible force of the air, as well as to the pressure arising from its gravity. If a barometer be placed near the perpendicular side of a high hill, wall, or building, when the wind is blowing violently against it, the mer- cury wUl probably remain nearly at the same height as if the barometer stood in an open place ; but the den- sity or gravity of the atmosphere ought to be considerably augmented by compression near the wall, on account of the obstruction it presents to the velocity of the wind ; consequently the mercury should be more elevated m a barometer placed there, than it would be were it fixed in an open situation at the same time, if the action of the atmosphere upon the mercury were solely the force arising from its gravity.
INTRODUCTION, XI
THE CHANGE of the MOON, in most parts of the globe, is more likely to Supposed in. be accompanied by stormy weather than the full moon ; and blowing weather prevails m"oo"n''upon'tii> more in dark nights than when much of the moon's disc is illuminated. By looking atmospiieric into the Nautical Almanac the lunar points will be seen. When the semi-diameter '"*" and horizontal parallax of the moon are greatest, she is in that part of her orbit nearest the earth, called the Perigee; and when the semi-diameter and horizontal parallax are least, she is in that part of the orbit farthest from the earth, called the Apogee.
An ingenious Frenchman has given a table of the chances of the changes of weather likely to happen at the lunar points, which he makes 10 in number. The principal of these lunar points are Perigee, Apogee, Change, and Full; and the changes likely to happen with these points, he thus marks :
The Perigee of the moon is likely to be accompanied by the greatest changes which happen from a single lunar point.
The new moon, next to the Perigee, is likely to be accompanied by the greatest changes of weather.
At new moon coinciding with the Perigee, the greatest changes may be expected, or 33 to 1 that a change of weather happens.
New moon coinciding with the Apogee, 7 to 1 that a change happens.
Full moon coinciding with the Perigee, 10 to 1 that a change happens.
Full moon coinciding with the Apogee, 8 to 1 that a change happens.
If new moon and Perigee coincide, when the sun is on the equator, the chance of a change of weather must be great.
If with the autumnal equinox, any of the lunar points coincide, there will be a great chance of a Ty-foong on the South coast of China, or of a storm in other parts near the tropic of Cancer.
The changes of weather do not happen precisely at the lunar points, but, like the tides, vary a little in time from these points ; for a change of weather often precedes 1 or 2 days the change of the moon.
THE VELOCITY of the WIND may be measured in various ways. An easy and velocity of the tolerably correct method is by estimating the motion of the detached clouds, when "'■"''• they are passing near the surface of the earth ; for in such case, their velocity will be nearly, though probably not quite so great as that of the wind. So that by measuring the interval of time betwixt the passage of the shadow of a cloud over two places, and comparing it with the distance between them, the velocity of the clouds moving with the current of wind may be ascertained.
This may be done at sea when two ships are at a considerable distance from each other in the direction of the wind, and sailing at the same rate on the same course : when the shadow of a cloud passing under the sun is observed to darken the sails of one ship, the time may be noted by a watch, and when the shadow of the same cloud darkens the sails of the other ship, the time ought also to be marked. The distance between the ships may be measured by sound, one of them firing a gun by signal, that the other may be enabled to note the time which elapses from seeing the flash to hearing the sound; the number of seconds in this interval multiplied by 1140, the number of feet which sound moves in a second, will give the distance in feet between the ships.*
* Experiments made by Mr. Millington make the velocity of sound to be nearest 1130 feet in a second, accelerated or retarded a little, by the direction of the wind ; but the state of the barometer made no differ- ence in its velocity. Dr. Olinthus Gregory, by various and numerous experiments, has found the velocity of sound to be 1100 feet per second at the temperature of freezing or 33°, and 1116 at the temperature of 66°;
c2
I
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Xii INTRODUCTION.
If the two ships are near each other, and the height of their mast-heads is known, the angle of one of theirmast-headsraay be measured by sextant, and these elements of a right angled triangle used to oljtain the distance between them ; w hich cannot be correctly ascertained by sounds, unless they are at a considerable distance from each other. In raeasurinti the velocity of the wind by the motion of the clouds, the mean of several observations ought to be taken.
The velocity of the wind may also be measured on shore pretty correctly, by means of a common kite. This is effected by letting the kite run out a certain length of loose line, and marking the time it takes in passing through the hand by watch ; then the time compared with the quantity of line run out will give the velocity of the wind nearly, but rather less than the truth : because the kite having a line fixed to it, and descending by its gravity, will be a little retarded in its horizontal motion.
Waves of the THE WAVES of the SEA are in general governed by the wind, and move in the **"• same direction, when the latter has continued steady for a considerable time; but this
regularity of the waves is often interrupted by local causes. Sometimes the waves run contrary to the wind ; at other times they are seen moving in various directions, running into, and crossing each other at different angles. During light winds, when a strong current is prevailing, there is generally a short confused swell in the opposite direction to the current, by attending to which experienced navigators may often foretell the course of the latter. Their velocity. There is reason to think, that few observations have been made at sea relative to the velocity of the waves, which is generally greater in the ocean than in shoal water near land ; because here, the mixed particles of sand and mud, and the friction occasioned by them and the ground, must considerably retard the regular progress of the waves.* The velocity of the waves may be easily measured by the common log, when a ship is running with them. To do this, when there is several knots of line out, or after the log is hove to obtain the velocity of the ship, mark the time to the nearest second by watch when the log is lifted npon the top of any wave, and mark the time when the stern of the ship is lifted up by the same wave: the length of line between the stern and the log will be the measure of the apparent velocity of the wave for the interval of time, to which must be added the velocity of the ship, and the sura will be the true velocity of the wave.
It may also be measured, when 2 ships, or a boat and a ship, near each other, are sailing on the same course with equal velocity, or when they are stationary during a calm. This is done by taking the angle of one of the ship's mast-heads with a sextant, the height of it being known from the deck or above the surface of the sea, and cor- rection must be made for the height of the eye above water. In this right-angled triangle, the perpendicular or height of the mast and the angles are given, to find the horizontal base line or distance between the ships, as in the case mentioned above, for ascertaining the velocity of the wind. At the time the angle of the ship's mast-head is taken, mark the time when the first ship is lifted up by a wave, and also the time when the other ship is lifted up by the same wave, and the distance between them, if they are both in a line with the course of the waves, will be tlie measurement of the velocity
therefore deduct \ a foot from 1100 for every degree below 33°, and add \ a foot for every degree of higher temperature.
* Dr. W. H. Wollaston found the velocity of the waves to be nearly 60 miles an hour by some observations taken at anchor in one of the Leith Smacks, close to the east coast of England. Captain David Thomson, an officer possessing much science, found the velocity of the waves to be 30 miles per hour, by repeated trials, when sailing directly before the wind with a strong'gale, off the Cape of Good Hope.
INTRODUCTION. XIU
of that wave for the interval of time. In order to approximate to the truth, the mean of several observations should be taken ; the velocity of the waves may be measured in this manner, although the two ships are not in a direct line with the course of the waves, by taking the angle between this course and one of the ships. In such case, the distance between the ships will be the hypothenuse of a right-angled triangle, which, with the angles, are given, to find the opposite side or perpendicular ; and this will be the measurement of the velocity of the waves, for the interval of time marked by M'atch.
These methods of measuring the velocity of the winds and waves are stated princi- pally with the view of exciting young navigators to rational amusement during a leisure hour; and that they may, by practice, improve themselves in the knowledge of maritime surveying, so essential to skilful navigators.
THE LUMINOUS APPEARANCE of the SEA,* which frequently happens, more Luminous ap. particularly between the tropics, or near them, in different parts of the globe, is pro- PJ^"«""of '^e diiced from various causes, not generally known to navigators ; although it has been noticed by Aristotle and Pliny, and by several naturalists in different ages, since their time.
Of various kinds of marine animals which emit light, the following appear to be best known.
First. — The Cancer Fulgens, discovered by Sir Joseph Banks, resembling the common shrimp, but smaller ; this I have often seen sparkling at the edge of the sea in dark nights, during the S.VV, monsoon, on the Malabar Coast ; and after being carried in a handful of sand, to be examined with a microscope, it continued to emit light till life was extinct.
Second. — Limulus Noctilucas, discovered by me in the Arabian Sea, April 12th, ] 798. Perceiving several luminous spots in the sea after day-light, and supposing them to be animals, I went in the boat and caught one, with some difficulty, as it endeavoured to avoid my band. It proved to be an insect somewhat resembling in appearance the wood- louse, and was about -j of an inch in length ; on examination with the microscope, it appeared to be formed by sections of a thin crustaceous substance, and while any fluid remained in the animal, it shone brilliantly like the fire-fly.
Third. — The Medusa Pellucens (or one of the species of blubber-fish), discovered by Sir Joseph Banks to be luminous, is a zoophyte, the most splendid of the luminous inhabitants of the ocean : the flashes of light emitted during its contraction are at times so vivid, as to affect the sight of the spectator.
Several other species of luminous medusae were discovered by Mr. Macartney, on the coasts of Kent and Sussex, of various forms and sizes, some of them very minute, not larger than the head of a small pin. Forster and other naturalists, have also discovered several different kinds of luminous marine animals besides those already mentioned.
Although the luminous appearance of the sea is generally produced by living ani- mals, nevertheless, some kinds of dead matter seem to give it a similar aspect at times, such as the exuviae of fishes or putrefactions.-]" I have sometimes carefully examined
* An excellent paper on luminous marine animals, by J. Macartney (Professor of Anatomy at the University of Dublin), was published in 1810 in Part 2nd of the Philosophical Transactions of the Royal Society of London,
t Putrid fish are known to shine in the dark ; this I have seen strangely exemplified at Bombay, where great quantities of a glutinous species of fish, resembling white-bait, are caught, and spread on the fields to be dried by the sun. These had a novel appearance in dark nights, the whole extent of the ground exhibiting a continued sheet of shining light.
(
Xiv INTRODUCTION.
the water of the sea when it was luminous, and could not discern any animation, but it appeared only to contain small particles of matter of a dusky straw colour, whicli dissolved with the slightest touch of the finger ; at other times the sea was evidently illuminated by small sparkling animals.
A peculiar phenomenon is sometimes seen in the Banda Sea, and other parts of the Eastern Seas ; and particularly in the Arabian Sea, between the east coast of Africa and the coast of Malabar, during the rainy monsoon. This I had an opportunity of once observing at midnight, when the weather was cloudy, and the sea particularly dark, but it suddenly clianged to a white flaming colour all round. This phenomenon bore no resemblance to the sparkling or glowing appearance observed on other occasions in seas near the equator, but the sea was of a splendid colour, white as milk, which did not continue more than ten minutes, when it resumed its former darkness.
This singular phenomenon has been also observed by several persons near the Malabar Coast, and in other parts, and it appears to be in a great degree elucidated by the observations of Mr. LangstafF, made in a passage from Port Jackson toward China. About half an hour after sun-set, the sea changed to a milky appearance, and the ship seemed to be surrounded by ice covered with snow. A bucket of water being hauled up, and examined in the dark, a great number of globular bodies were discovered, linked together, each about the size of a pin's head, the chains thus formed did not exceed three inches in length, and emitted a pale phosphoric light. This extraordi- nary appearance of the sea was visible two nights; but as soon as the moon exerted her influence, the sea resumed its natural dark colour, and exhibited distinct glittering spots, as at other times. Mr. Langstaff''s observations seem to shew, that the diffused light of the sea is produced by an assemblage of minute medusae on the surface of the water.
Mr. Macartney has seen streams of light on the surface of the sea, at different times, on the southern coasts of England ; and upon examination, a gallon of sea water in a luminous state, after being strained, left above a pint of small medusae He has also under such circumstances, perceived the sea to yield more support in swimming, and the water to taste more disagreeably than usual.
The surface of the sea is usually more subject to be luminous after long calms and sultry weather than at any other time; for then, it abounds with minute medusae and small marine animals generated in calm weather, which render it foetid both to the smell and taste. At such times the sea becomes easily illuminated, by the least dis- turbance of a squall, or any thing that produces agitation or friction on its surface. The porpoise, dolphin, dorado, and other fishes, therefore, often reflect a -vivid light when swimming near the surAice, which has induced some persons to ascribe the property of emitting light to several fishes : but upon close examination, the bodies of those fishes were found to be covered with minute spherical particles which adhere to their surface, apparently the same that illuminated the whole of the sea at the time, and in all pro- bability were a minute kind of medusae.
The small particles of matter of a dusky straw colour, mentioned above, which were examined by me (but not with a microscope), and appeared destitute of animation, might nevertheless have been the minute medusae discovered by Mr. Macartney, and called by him Medusa Scintillans, which he thinks to be the most frequent cause of the luminous appearance of the sea. When at Heme Bay, a small watering place on the northern coast of Kent, in October 1804, he observed the sea to be luminous several nights, and took up a considerable quantity of the water, which emitted no light when at rest ; but on the slightest agitation of the vessel which contained the
INTRODUCTION, XV
water, a brilliant scintillation was perceived towards the surface ; and when the vessel was suddenly struck, a flash of light issued from the top of the water, in consequence of so many points shining at the same moment. Having strained a quantity of the lumi- nous water, a great number of transparent corpuscles were obtained upon the cloth, and the water which had been strained did not afterwards exhibit the least light. Some sea water, which had been rendered particularly clear by repeated filtrations, was then put into a large glass, and having floated in it a fine cloth, on which he had previously collected a number of luminous corpuscles, several of them were liberated, and became distinctly visible in their natural element, by placing the glass before a piece of dark coloured paper. They were observed to have a tendency to come to the surface of the water, and after the glass was kept steady sometime, they were found congregated together, and when thus collected in a body, they had a dusky straiv colour, although individually they were so transparent as to be invisible, except under parti- cular circumstances. In the air, they appeared like globules of water; they were more minute than the head of the smallest pin, and upon the slightest touch they broke and vanished from the sight. The motions of these creatures in the water were slow and graceful, not accompanied by any visible contractions of their bodies ; and after death they always subsided to the bottom of the vessel.
A beautiful illumination of the surface of the sea is sometimes reflected from the broken water or waves at the head of a ship, occasioned by her velocity through the fluid, when it abounds with those animals which emit light. Once I experienced a splendid instance of this kind near the equator, when the quantity of gleaming light reflected from the waves under the weather bow of the ship, against the white fore-sail, was sufficient to enable me to read any pages of a book, if not pi'inted with a very small type, although the night was otherwise dark at the time.
THE TEMPERATURE of the SEA is a phenomenon hitherto but little inves- Temperature tigated, although it appears to be closely connected with the improvement of nau- °' ""^ '™' tical science ; the following observations may, therefore, be not altogether unimportant to navigators.
It has been thought that the temperature of the ocean was subject to little variation, particularly between the tropics; the temperature of its surface, however, is affected by changes of the superincumbent atmosphere, as well as by other local or adventitious causes,
1st. When the atmosphere has a low temperature, a portion of its cold is imparled to the surface of the ocean, by which the temperature of the water is diminished.
2nd. Tempestuous weather raises the temperature of the sea, an effect which is pro- bably produced by the agitation or friction of the broken waves, the particles of water rubbing against each other.
3rd. Currents have a more powerful influence than any other cause in changing the temperature of the surface of the ocean ; and it may be here observed, that the same rule is applicable in this case as that already stated in regard to winds, under the ar- ticles Trade Winds and Marine Barometer, viz.: That in either hemisphere a current proceeding from the cold polar regions towards the equator, diminishes the tempera- ture of the sea ; whereas, a current running from the inter-tropical regions towards either pole, raises its temperature. It is surprising how long the great bodies of cur- rents preserve their original temperature ; that known by the name of the Gulf Stream loses only two degrees of its original warmth in running 1300 miles into a cooler cli- mate, it being 81° in summer inlat. 39° N. ; and in passing the bank of Newfoundland,
Xvi INTRODUCTION.
it is several degrees warmer than the sea in its vicinity; thus the experienced navigator is enabled to ascertain when he gets into the Gulf Stream merely by drawing a bucket of water, and feeling its temperature.
4thly and lastly. The depth of the sea appears, also, to have a great influence on the temperature of its surface, for the immense body of water contained in the ocean preserves its heat: whereas, in places of little depth, the surface of the water is cooled by increased evaporation.* The temperature of the ocean, therefore, may be expected to be hi"her than tliat in seas which have little depth of water, in the same parallels of latitude." This seems to be verified by the experiments and observations of Dr. John Davy, during his voyage to Ceylon ; as in approaching the land of Table Bay at the Cape of Good Hope, from the westward, the temperature of the sea decreased 2°, and it also decreased 2° when the Island of Ceylon was closely approached, although the bank of soundings does not extend far out from either of these places.
Sir John Herschel in a letter, dated Cape of Good Hope, July 7th, 1834, states that from the time of leaving England, in November 1833, the temperature of the sea increased with regularity, until in lat. 4° N., Ion. 21° 10' W., where it attained its maximum, and on the average of six days' observations, about the 6th December, it was 81° of Fahrenheit. The temperature decreased, also, regularly, in proceeding from the equator to the southward, it being 64°, 2, on the 12th January, 1834, then in lat. 34° 16' S., Ion. 11° 49' E. On the following day, the 13th, it rose to 70°, 5, in lat. 34° 35' S., Ion. 14° 42' E., which was attributable to a part of the warm stream that sets round the Cape to the westward ; as it decreased to 68°, 3 on the 14th, in approaching the land, and to 59°, 5 when Table Bay was entered, on the 15th of January 1834, which corresponds with other observations, that the temperature of the sea decreases in the proximity of land or shoal banks.
In calm and settled weather the temperature of the sea was found, by Dr. John Davy, to reach its maximum about one or two hours after noon ; and its minimum about sunrise.
Were the temperature of the sea, as well as that of the atmosphere, conjointly regis- tered in the journals of navigators, several times every 24 hours, it would assist greatly the improvement of nautical science; and the proximity of land or shoal banks, might probably be ascertained by carefully observing the temperature of the sea.
The late Captain J. P. Wilson, of the Company's ship Hythe, a very scientific officer, has ascertained by careful observation that the temperature of the central part of the stream of westerly current which prevails along the verge of Cape Aguilhas Bank, is about 8° or 9° higher than that of the sea beyond the limits of the stream of current ; and as the maximum of temperature is in the middle of the stream of current, a ship may be kept in it, by attending to changes of temperature in the surface water, and thereby be enabled to accelerate her progress to the westward during adverse winds.
currenu. CURRENTS, or TIDES, are generally experienced more or less in most parts
of the ocean. Where trade winds or monsoons blow steadily, the current runs mostly with the wind ; but at times, no current is experienced, and sometimes it sets contrary to the prevailing wind.
In high latitudes, in the open ocean, the current seldom runs so strong as in the vicinity of the equator, where it is very changeable, running in parts of the Pacific and Indian Oceans, sometimes at the rate of from 20 to 60 miles in 24 hours.
* See the sequel under the article Squalls, at p. vii.
INTRODUCTION. • XVll
The current near the equator, and also in most places of the open sea, sets more frequently to the westward than to the eastward : and when the current is running in one direction on the surface, it is sometimes running in an opposite, or oblique direc- tion, underneath. Therefore the usual method of trying the velocity and direction of the current in a boat, by sinking a kettle or pot to the depth of 60 or 70 fatlioms, is seldom found to agree with the admeasurement of the same by chronometers. But since navigation has been improved by the use of the latter, the direction and velocity of currents are now more correctly ascertained.
The tides, in high latitudes, generally rise and fall more than in low latitudes, and it Tides. has been said, that the perpendicular flux and reflux was very little within the tropics, which is not always the case. At the head of the Gulf of Carabay, in lat. 22° N., the perpendicular depth of the rise and fall of the tides is from 30 to 36 feet at the full and change of the moon. At the same time, it is 20 and 21 feet in Surat Road ; and from 15 to 17 feet in Bombay Harbour.
In the Gulf of Martaban, which is far within the tropics, the perpendicular depth of the rise and fall of the tide, at the full and change of the moon, is 23 and 24 feet, and off Rangoon Bar about 20 or 21 feet.
In Gaspar Straits, within 2^° of the equator, there is sometimes, from local causes, a rise and fall of 16 or 17 feet on the springs ; but the rise and fall of the tide, is seldom so great as this, in places situated near the equator.
Although in most places, the tide flows twice every 24 hours, this is not universally the case within the tropics,* for amongst several of the eastern islands, the tide flows only once in 24 hours ; the passage of the moon over the meridian generally makes high water at these places ; but in some parts, the tide is highest when the moon is near, or in the horizon.
MAGNETISM is one of the phenomena of nature which seems to elude the defini- Magnetism. tions of science ; several hypotheses, indeed, have been formed, and many attempts made to discover its elementary principles, yet they appear to be still very imperfectly known. Formerly some philosophers were of opinion, that a great central magnet in the inter- nal part of our globe was the cause of all the magnetic influence; while others consi- dered the cause to be merely atmospherical. But the productive cause of magnetism Productive seems neither confined within the earth, nor to the atmosphere, as both are known ""'"• greatly to affect the magnetic needle, and later discoveries have shewn its connection with electricity.
Many of the masses of rocks or mountains which form a considerable portion of the earth are partly composed of metallic matter, and exert a powerful magnetic influence.
The sun has an influence on the needle, producing a diurnal variation, which has been observed to increase progressivelyt with the altitude of that luminary.
The Aurora Borealis, which is considered to be an electrical phenomenon, is also thought to have an effect upon the magnetic needle; and it appears to be influenced by several other secondary causes.
Mr. John Churchman, an American, who was a member of the Imperial Academy Hypothesis of
Cliurcliman
and Walker.
* In many places far beyond the tropics, the tide likewise flows only once in 24 hours, particularly on the southern coast of Van Diemen's Land ; but at Port Dalrymple on the North coast, the tide flows twice in 24 hours.
t This I have experienced several times during fine weather at sea, in observing a series of azimuths ; com- mencing when the sun's altitude was 3° or 4°, and continuing the observations until it was 25° or 30° above the horizon. The diurnal variation of the needle has been long known, and often observed upon land.
d
^
Xviii INTRODUCTION.
of Sciences, St. Petersburg!), and Mr. Ralph Walker, the civil engineer, formerly of Jamaica, appear to have published, nearly at the same time, an ingenious hypothesis, with a view of solving all magnetical problems, relating both to the vertical and hori- zontal declination of tiie needle. In a diagram of the two hemispheres, on the plane of the equator, drawn by Mr. Walker upon this principle, there are two magnetic poles, represented at difterent distances from the poles of the earth, and revolving round the latter in unequal periods of time. Tiie North Magnetic Pole is placed for the year 1794, in lat. 71° N., Ion. 80° W. ; the South Magnetic Pole in lat. 65° S., Ion. 130° E. ; ami by the intersections of the magnetic meridians with the terrestrial meridians, the \ariatK)n of the needle might be found by inspection on these hemispheres for all places on the surface of the globe, were the positions of the magnetic poles well ascertained and correctly laid down, and the needle not subject to aberrations from various causes already mentioned. But exclusive of the perpetual aberration of the needle from permanent causes of nature, it is likewise subject to adventitious and local attractions, lialile to operate in a considerable degree against the accuracy of any theoretical solu- tions.
Mr. Churchman supposes the periodical revolution of the North Magnetic Pole round the North Pole of the earth to be 1,096 years ; and the revolution of the South Magnetic Pole round the South terrestrial Pole to be 2,289 years, its motion being much slower than that of the North Magnetic Pole, which is the cause of perpetual irregu- larities of the variation of the needle. He is of opinion, that when one of the Magnetic Poles is in the zenith of any place, magnetic tides, or great inundations, will there be experienced ; and when the Magnetic Pole is far distant from any place, the sea will recede, and alluvial land will be formed. Mr. Walker, besides his diagram for show- ing the horizontal declination of the needle, has drawn two hemispheres on the plane of the equator, for shewing the vertical declination or dip of the needle for all places on the globe ; and in addition to his improvements on steering compasses, he has in- vented a meridional compass for shewing the quantity of variation by inspection at any time of the day.*
The celebrated Dr. Halley was of opinion, that the variation and dip of the needle could not be resolved consistently, on the supposition of the earth having only one magnetic axis, and two magnetic poles; and he inferred, that two magnetic poles must exist in the northern hemisphere, and two also in the southern hemisphere of the earth, in order to account for the discordant magnetic changes.
Professor Hansteen, justly esteemed for his profound investigations of magnetical phenomena, and for his researches in Siberia and other places, to ascertain the mag- netic influence and intensity, has discovered the existence of a magnetic pole in that country, Siberia, which leaves no doubt that there are two magnetic poles in the northern hemisphere: and as the late expeditions of our enterprising navigators have proved the existence of another magnetic pole in lat. 70° 5^' N., ion. 96° 4()f' W., by the observations of Captain James Clarke Ross, Dr. Halley's inference seems to have been correct, and may soon be demonstrated by similar researches in the southern hemis- phere, where the existence of two magnetic poles will probably be discovered. f
* The late Mr. J. Garnett, an ingenious philosopher and astronomer, who resided long in America, where he superintended the publication of an Astronomical Epheraeris, states that he used the common ring dial for the same purpose at sea as well as on land, which shews the true meridian within 1° of the truth, at any time when the sun's altitude is not too great ; and consequently, the variation of the needle from the true meridian.
t A scientific expedition, consisting of H. M. ships Erebus and Terror, under the command of Captain James Clarke Ross, which sailed from England in October 1839, will, in all probability, throw much light on this point ; the investigation of the phenomena of magnetism being the primary object of the expedition.
INTRODUCTION. XIX
According to the recent researches of Professor Ilansteen, tlie earth has four majr- netic poles, all revolving in the neiglibourhood of the geographic poles ; an«l the periods of these revolutions are respectively about 4,600, 1,740, 1,300, and 800 years. These times, though long, as historical periods, are short, compared with many of those cycles of which geological researches and astronomical calculations seem to prove the existence.
THE VARIATION OF THE COMPASS, when mentioned in this work, is in- variationof tended only for tiie navigator to make proper allowance in steering from one place to """^"'"p*" another, and not as a guide for estimating the longitude, which was practised about .30 and 40 years ago by mariners, before the use of chronometers and lunar observations became general.
In places where the variation changed quickly, in sailing nearly on a parallel of lati- tude, navigators were formerly eager to embrace its aid as an approximation to the true longitude; but compasses being subject to many errors from various causes, the longitude ascertained by means of the variation could never be trusted to with any reasonable degree of confidence. The variation of the needle is in a state of continued change in most places of the globe, and there is also a diurnal and annual variation of the variation ; besides the same compa«ses will alter when taken from one ship into another, and if shifted to different situations in the same ship. And in some places of the globe, although a compass be stationary in a ship, the needle seems to be subject to an aberration of several degrees, proportionate to the angle that the ship's head makes with the magnetic meridian.
THIS ABERRATION OR LOCAL ATTRACTION OF THE NEEDLE, A>.~>or
Captain Flinders constantly experienced during his survey of the coasts of New Hoi- oTthe^'needie!" land, which is recorded in the Philosophical Transactions of the Royal Society for 1805. With the compass placed amidships in the Investigator, the bearing of points of land on the South coast of New Holland, taken immediately before and after tack- ing, differed sometimes 8° or 9° when the ship's head was changed nearly from East to West ; but there was little or no difference when the direction of the ships head was North or South. This difference in the direction of the magnetic needle from itswjea?* state, was easterly when the ship's head was West, and westerly when it was East. When the ship's head was North or South, the needle continued in its mean state, and shewed a variation from the true meridian, nearly equal to the medium between w hat it shewed when the ship's head was East and when West ; and the aberration of the needle was nearly proportionate to the number of points which the ship's head was from the North or South.
This aberration of the needle, arising from a change of the ship's head, varies in dif- ferent ships at the same place, according to their size, and the quantity of iron they contain, and it appears to be greatest in small ships : but in places near the equator, where there is little variation, this aberration cannot be perceived, for it increases in proportion to the distance from the magnetic equator, toward the poles in botli hemispheres.
Captain Flinders was of opinion, that the magnetism of the earth, and the attraction of the iron in a ship, acted as a compound force in producing the error of variation by the changeof a ship's liead ; and he thought that the error at any direction of the a kips head, would he to the error when her head teas East or West, at the sauie dip of the needle, as the sine of the angle betiveen the ships head and magnetic meridian was to the sine of eight points, or radius.
d 2
XX INTRODUCTION.
Since the time of Vancouver, Flinders, Bain, and others, alluded to by Captain Horsburgh, the subject of local attraction has been carefully investigated by Professor Barlow, and fully treated by him in his " Essay on Magnetic Attractions." It has therefore been thought desirable to omit the remarks which have appeared in the former editions of this work, and to substitute for them the following practical directions on the subject, which were drawn up with great care and attention from Mr. Barlow's work and other authentic sources, and published in the Nautical Magazine for April 1037.
DIRECTIONS FOR ASCERTAINING THE AMOUNT OF THE LOCAL ATTRACTION OF A
VESSEL ON THE COMPASS.
The variation of the compass as deduced from observation at sea in different parts of the world, was long considered by seamen as the true variation, or, in other words, that it was the real angle which the magnetic needle makes with the true meridian. And although certain discordances in compass bearings were noticed at different periods by the navigators of former days, yet it nowhere appears that they discovered the cause of those discordances to be the iron distributed through their own vessels ; the attractive power of which was continually acting with more or less force on the magnetic needle, sometimes in conjunction with, and sometimes in opposition to, the magnetic influence of the earth.
The earliest notices we have on record of this deviation of the needle from the mag- netic meridian are given by Sturmy in his " Mariner's Magazine," published in 1700, and by the celebrated circumnavigator, Captain William Dampier, in the account of his voyage to New Guinea. In the quaint language of his time, Dampier thus alludes to it: " Another thing that stumbled me here was the variation which, at this time, by the last amplitude, 1 found to be 7° 38' W,, whereas the variation at the Cape of Good Hope it was then computed, and truly, about 11°, and yet a while after this, when I had got ten leagues to the eastward of the Cape, I found the variation but 10° 45' W. ; whereas it should have been more than that at the Cape. These things 1 con- fess did puzzle me." This irregularity was no doubt the effect of the iron in the vessel, and although Dampier had a shrewd inquiring mind, it was not to be expected that he should at once hit upon the discovery of its causes. Those causes lay concealed amidst the depths of science, and their discovery was reserved for the persevering efforts of men of the present more enlightened age. Aware, however, of the value of such observations, Dampier very properly recorded them with the view of assisting Halley in the construction of his variation chart,* and recommended all navigators to do the same.
* Halley published this chart, which was the first of its kind, in the year 1700. He had collected a vast number of observations of the variation, which having noted in their proper places on a Mercator's chart of the world, he was enabled, by drawing lines through them, to trace the corresponding degrees of variation, or, in other words, to shew the course of the magnetic curves. Another chart of this kind was published by Mountain and Dobson in 1744, and another in 1756-7, and from the apparent facility of observing the varia- tion, it was even seriously recommended to mariners as a means of ascertaining their longitude. The inefficiency of such means is so obvious, that these charts are now only used for giving a general view of the amount of the variation in different parts of the world. Yeates published another chart in 1817; and more recently Professor Barlow has given us all the modern observations in a chart of two sheets, which he proposed to follow up by a variation globe.
INTRODUCTION. XXI
We find nothing that throws any further light on the subject of local attraction until the time of Captain Cook, when the attention of Mr. Wales, who accompanied him as astronomer, was awakened by the differences which he found in his observations. He states distinctly, that " variations observed with the ship's head in different positions, and even in different parts of her, will materially differ from one another ; and much more will observations observed on board different ships." Mr. Wales gives instances of these differences amounting to 10°.
The voyage in which he made these observations lasted from 177G to 1780 ; and in 1793, we find that the celebrated French naval surveyor, M. Beaulemps Beaupre, when employed in the Recherche looking for La Peyrouse, abandoned the old system of using compass bearings in consequence of meeting with difl'erences of several degrees in the variations. We may here remark that M. Beaupre was among the first to adopt that excellent system of obtaining the true bearing by an angle referred to the sun's azimuth.
In 1790, however, the first direct mention of local attraction was made by Mr. Downie, when master of H.M.S. Glory, in Walker's Treatise on Magnetism. " I am convinced," says Mr. Downie, "that the quantity and vicinity of iron in most ships has an effect in attracting the needle, for it is found by experience that the needle will not always point in the same direction Avhen placed in different parts of a ship; also, it is very easily found that two ships steering the same course by their respective com- passes, will not go exactly parallel to each other, — yet when these compasses are on board the same ship they will agree exactly."
But, notwithstanding the important discovery that such anomalies existed in a ma- chine of so much consequence to the safety oi ships as the mariner's compass, they still remained unheeded, until the return of Captain Flinders from the survey of Australia, when, in consequence of his representations to the Lords Commissioners of the Admiralty, he was directed to make a series of experiments on board one of his Majesty's ships at Sheerness.
The results of these experiments are thus stated : —
1st. That a compass gave different bearings of the same object when placed in dif- ferent parts of the ship.
2d. That when the ship's head was on the magnetic North or South, no effects arose from local attraction, proving that when the ship was in that position the attrac- tion of the various masses of iron on board acted in unison with the magnetism of the earth.
3d. That when the ship's head was East or West, the effects of local attraction were greatest, and that at the intermediate points of the deviation of the needle varied nearly in the proportion of the sine of the angle between the bearing of the ships head and the magnetic meridian to radius.
4th. That the maximum of variation, in the same compass, would be different in different parts of the world, or, in other words, that the force of the local attraction of the vessel varied with the dip of the magnetic needle, or in proportion to the distance of the magnetic equator.
Flinders died in 1814, and the subject of local attraction lay almost untouched until Mr. Bain, a master in the royal navy, took it in hand, and wrote a pamphlet on it, which appeared in 1817. There was a great deal of merit in this little production ; all his were sound opinions; but, although his remarks and observations were accom- panied with ample proofs of the importance of attending to them, he failed to give those plain and straightforward directions which the seaman looks for. The subject
Xxii INTRODUCTION,
was lastly taken up by Professor Barlow, a name well known in the annals of science. The polar expedition of 1818 afforded an admirable opportunity for confirming- still further the laws laid down by Flinders, as the ships not only passed through a con- siderable variety of variation, but necessarily approached the north magnetic pole. Constant observations were accordingly made on board the Alexander and Isabella, at the suggestion of the professor, and it was found, before they had nearly reached Greeidancf, that the compasses of one ship differed as much as 11° from those of the other, and that the same compass gave results differing 10° in different parts of the same ship. As the two vessels proceeded up Davis Straits, the compasses became slusgish; and in the subsequent voyage of Sir Edward Parry, as he passed through Barrow Strait, they became totally useless— thus confirming the conclusion of Flinders, that, although the magnetic force of the earth wonld be greatest at the magnetic pole, yet its horizontal or directive power would then entirely cease, having become gradually less in proportion as the angle increased, which the dipping needle makes with the horizontal plane. But while the horizontal needle is thus forsaken, as it were, by the earth's magnetic power, the various magnetic bodies in the ship uhich surround it are still acting on it with a directive force which relatively increases as the directive force of the magnetic pole diminishes.
The discorda'nces in the variations observed at sea, and the difficulty of arriving at the actual inclination which the magnetic meridian makes with the true one, can only be attributed to the want of a due observance of the foregoing facts. But these facts are now so universally admitted, that it is unnecessary to multiply proofs either of their existence or of the evil consequences which may arise from their neglect. We will therefore at once proceed to the best practical methods of determining the local attrac- tion of any vessel, and of applying the proper correction for its effects to the compass courses.
There are two modes of effecting this problem— the first is, observing by a compass, on board, the bearing of a distant object on shore, while the ship makes a complete circuit, or passes through all the points of the compass. The second is, by means of two compasses, one of which is placed on shore at any convenient distance, and the other remains on board, while the ship's head is made to perform a similar revolution.
The former method is the most independent, as it requires only one observer; but then it is necessary that the object on shore should be at a distance of several miles, in order that the parallax of the vessel in the circuit she necessarily makes in order to place her head on every point of the compass, be so small as to subtend an insensible angle at the object. The distance requisite to fulfil the above condition will vary from four to ten miles, according to the scope of the cable, or the looseness of the moorings. Assuming this angle to be insensible, or so small as to be within the uncertainty of observation, the bearings then made of the object may be considered as taken from a single spot, and therefore, if it were not for the effect of local attraction, they would of course be all alike.
The correctness of this method evidently depends on the truth of the above assump- tion, but as a suitable object does not occur at every anchorage, we shall proceed to the second method, which is equally correct, but which requires the co-operation of another observer.
This method consists in taking the bearing of the compass on board from another on shore, at the same instant that the bearing of that on shore is observed from the couipass on board. It is evident, that if the two compasses employed have previously agreed in every respect, that each pair of observations would be the reverse of each other, so that if
INTRODUCTION.
xxni
the compass on board bore S.W. from tliat on shore, that of the shore would bear N.E. from the compass on board ; but in consequence of the effects of local attraction the compass on board will, on almost every bearing, differ considerably.
We will now suppose that a ship lying at Spithead, having all her guns, and cargo, and spare anchors on board, is desirous of obtaining her local attraction by a single observer.
As it is necessary that the ship's head should be placed on each point of the com- pass, the opportunity of slack water should be taken, and a warp should be properly laid out to a buoy, or to another vessel, in order to secure her performing the revolution gradually. Select any vvell-defined object on shore, such as a remarkable tree or house on one of the most distant ridges. The azimuth compass should be employed, as it is fitted with sight vanes, and the circumference of the card is divided into degrees ; but all the observations must be made from the binnacle, precisely over the usual position of the steering compass.* Then, as the ship slowly presents her head to each point of the compass, the bearing of the object is to be carefully observed, and, if practicable, a moment should be allowed to elapse after the ship's head arrives on each of the different points, so that no error may arise from the swing of the compass.
The bearings as they are obtained must be immediately noted in a table, arranged in the following form, the column No. 1 having been previously written.
When the North end of the needle is drawn to the eastward, the local attraction is marked — , and when to the eastward + .
No. 1.
No. 2.
Direction of Ship's Observed Bearing of Head. I Object.
North N. by E. NN.E. N.E. by N. N.E.
N.E. by E. E.N.E. E. by N. East. E. by S. E.S.E. S.E. by E. S.E.
S.E. by S. S.S.E. S. by E.
N.18 N. 17 N. 16 N. 15^ N. 14 N. 14
N. 13| E.
N. 13 N. 12
E.
E.
N. 10 E. N. 9iE.
E.
N. 10 N. 10 N. 11 N. 13 N. 14
210|
No. 3.
Correct Bearing of Object.
N. 17 E.
Local At- traction.
+ 1
0
—1
-H
—3 —3
-H
—5
—7
71
'2
—7
—7 —6
No. I.
Direction of Ship's Head.
South S. by W. S.S.'W. S.W.byS. S.W.
S.W. by W. W.S.W. W. by S. West W. by N. W.N.W. N.W. byW. N.W.
N.W. by N. N.N.W. N. by W.
No. 2.
Observed Bearing of Objecu
N. 14 E. N. 16 E. N. 17 E. N. 18 E. N. 19 E. N. 20iE. N. 22 E. N. 24 E. N. 24 E. N. 25 E. N. 25 E. N. 24 E. N. 23 E. N. 22|E. N. 20iE. N. IsJe.
333 210i
543i
No. 3.
Correct Bearing of Object.
N. 17 E.
No. 4.
Local At- traction.
—3 — 1 — 0
+ 1
+ 2 + 3^ +5 + 7 + 7 + 8 + 8 + 7 + 6 +5i + H
+ H
* Should it be inconvenient to place the azimuth compass immediately over the binnacle, select any other position for it amidships on the vessel's deck, and in this case let the direction of the ship's head be noted by both the compasses when the bearing of the object is taken, in order to obtain the bearing of it from the steer- ing compass, from which it may not be visible, l^he number of degrees between the ship's head and the object by the azimuth compass, applied to the direction of the ship's head by the steering compass, will give the bearing of the object from it, as well as if it had been actually observed.
XXIV
INTRODUCTION.
If time should permit, it would be advisable to repeat this series of observations, in order to guard against any mistakes, and, if practicable, to swing the ship's head round in the op|)osite direction to that of the first revolution.
The observer having now filled up column No. 2 with the observed bearings, and being satisfied with their accuracy, he is to add them all together, making in this example 54.3;^, which being divided by the number of observations (32), the result (17) will be the mean or true magnetic bearing of the object from the ship, and there- fore 17° is to be entered on every line of column No. 3.
The differences between the figures in columns Nos. 2 and 3 are then to be regularly inserted in column No. 4, and as they represent the effect of the local attraction of the ship upon the needle in the binnacle, for every successive point of the compass, they cannot be more compendiously placed for the ready reference of the navigator in cor- recting his day's work. To prevent the chance of his applying them the wrong way, it will be prudent to mark them all with the signs + or — according as they are to be applied to the right or left of the course to be corrected.
Or perhaps a table of the points ready corrected, such as the following, might to some seamen be more satisfactory; but whichever table is adopted, a copy of that table should be hung in the binnacle, and every person on board who keeps a reckoning should have a copy of it attached to his traverse table.
|
Courses by Com- |
Courses corrected for Local |
Courses by Com- |
Courses corrected for Local |
Courses by Com- |
Courses corrected for Local |
Courses by Com- |
Courses Corrected for Local |
|
pass. |
Attraction. |
pass. |
Attiaclion. |
pass. |
Attraction. |
pass. |
Attraction. |
|
North |
N. °1 W. |
East |
S.85 E. |
South |
S. °3 W. |
West |
S. 83 W. |
|
N.byE. |
N. UJE. |
E. by S. |
S.71|E. |
S. by W. |
S.12 W. |
W.byN. |
N. 86JW. |
|
N.N.E. |
N.231E. |
E.S.E. |
S.60 E. |
S.S.W. |
S. 22iW. |
W.N.W. |
N. 75|W. |
|
N.E.byN. |
N.35JE. |
S.E.byE. |
S.49J-E. |
S.W.byS. |
S. 32f W. |
NW.byW. |
N. 63J-W. |
|
N.E. |
N.48 E. |
S.E. |
S.38 R. |
s.w. |
S.43 W. |
N.W. |
N. 51 W. |
|
N.E.byE. |
N.59iE. |
S.E. by S. |
S.27JE. |
S.WbyW. |
S.52JW. |
N.W.byN. |
N. 39iW. |
|
E.N.E. |
N. 71 E. |
S.S.E. |
S.I8|E. |
W.S.W. |
S.62^W. |
N.N.W. |
N. 26 W. |
|
E.byN. |
N.82|E. |
S. by E. |
S. SiE. |
W.by S. |
S.71fW. |
N.byW. |
N. 12f W. |
Thus if a ship was apparently steering S.E. by the compass, she would be actually steering 7° to the southward of that point or S.E.fS. and in working the day's work, the — 7° must be applied to that course ; but if on the other tack she should lie up North, only 1° would be the correction to be applied, and that with the contrary sign.
The above mode of discovering the local attraction is so simple and so perfectly in every seaman's power, that surely none but the most perversely indolent will continue to blunder through their voyages as heretofore. Every ship in the Queen's service should be ordered to make a return to the commander in chief of the local attraction, in a form similar to the table we have given, and every six months the experiment should be repeated and reported.
Having shewn the means by which the seaman may obtain the desired object with a single compass, we will now describe the second method, which, however, requires the assistance of two compasses and two observers. The two compasses selected for the operation, should precisely agree with each other. One of tliem mounted on a tripod stand is said to be taken on shore at a short and convenient distance from the ship, and so placed as to be easily seen from the other compass which remains on board in Its proper position in the binnacle, from whence the principal observer will watch the
INTRODUCnON,
XXV
progress of the ship's head and by some preconcerted signals he will communicate the instant of his making each observation to his assistant on shore.
The best means of doing this will be by a light staff in his hand with a little flag or a white handkerchief fixed to it. The process would be as follows : — The proper warps being prepared as in the former experiment, to check tiie rapidity of the ship's swinging, and to steady her head on each point of tlie compass for an instant, the observer on board displays his little flag, in order to warn the observer on shore to look out. A few moments may elapse with the flag up, while the ship is becoming steady and the compass settling. Then commencing at any point on which the ship's head happens to be, the bearing of the shore compass is taken, and at the same instant the flag is put down. The assistant on shore at the instant of the disappearance of the flag, observes the bearing of the compass on board, and each observer carefully registers his observation. The ship's head is then placed on the next point of the compass, when the same process is followed, and so on throughout all the other points. The observations are then tabulated, according to the following form, and the direction of the ship's head being placed against each pair of observations, their difference shews the deviation of the needle on board from the magnetic meridian. When the proper signs are applied as before explained, this table shews the effect of the local attraction for each point of the compass, and is ready for use.
|
Direction of Ship's |
Bearing of Shore Compass from on |
Bearing of Com- passs on Board from |
Difference or Local |
Direction of Ship's |
Bearing of Shore Compass from on |
Bearing of Com- pass on Board from |
Difference or Local |
|
Board. |
Shore Compass. |
Attraction. |
Board. |
Shore Compass. |
Attraction. |
||
|
North |
s. s'e W. |
N. 36 E. |
o 0 |
South |
S. 32 W. |
N. 31 E. |
o + 1 |
|
N. by E. |
S. 30i W. |
N. 34 E. |
-H |
S. by W. |
S. 33 W. |
N. 31 E. |
+ 2 |
|
N.N.E. |
S. 30 W. |
N. 34^ E. |
-H |
s.s.w. |
S. 34 W. |
N. 31 E. |
+ 3 |
|
N.E. byN. |
S. 32 W. |
N. 34i E. |
-n |
S.W.byS. |
S. 34iW. |
N. 31 E. |
+H |
|
N.E. |
S. 29 W. |
N. 34 E. |
—5 |
S.W. |
S. 35 W. |
N. 31 E. |
+ 4 |
|
N.E. by E. |
S. 29 W. |
N. 341 E. |
— 5J |
S.W.by W. |
S. 34 W. |
N. 30J E. |
+^ |
|
E.N.E. |
S. 29 W. |
N. 34^ E. |
-5J |
W.S.W. |
S. 38 W. |
N. 33 E. |
+ 5 |
|
E.byN. |
S. 25 W. |
N. 33 E. |
—8 |
W. by S. |
S. 40 W. |
N. 34 E. |
+ 6 |
|
East |
S. 27 W. |
N. 34 E. |
-7 |
West |
S. 40 W. |
N. 341 E. |
+ H |
|
E. by S. |
S. 27 W. |
N. 33 E. |
—6 |
W. by N. |
S. 41 W. |
N. 35 E. |
+ 6 |
|
E.S.E. |
S. 27 W. |
N. 33^ E. |
—6 |
W.N.W. |
S. 40 W. |
N. 35 E. |
+ 5 |
|
S.E. by E. |
S. 27 W. |
N. 324 E. |
-H |
N.W.byW. |
S. 39 W. |
N. 35 E. |
+ 4 |
|
S.E. |
S. 28 W. |
N. 32 E. |
—4 |
N.W. |
S. 40 W. |
N. 36 E. |
+ 4 |
|
S.E. by S. |
S. 28 W. |
N. 32 E. |
—4 |
N.W. byN. |
S. 40 W. |
N. 38 E. |
+ 2 |
|
S.S.E. |
S. 27 W. |
N. 30 E. |
—3 |
N.N.W. |
S. 39 W. |
N. 37i E. |
+ H |
|
S. by E. |
S. 30 W. |
N. 31 E. |
—1 |
N. by W. |
S. 38 W. |
N. 38 E. |
+ 0 |
|
Then from the foreg |
oing, the following table may also be formed: |
||||||
|
Courses by Com- |
Courses Corrected |
Courses by Com- |
Courses Corrected |
Courses by Com- |
Courses Corrected |
Courses by Com- |
Courses Corrected for Local At- |
|
traction. |
traction. |
traction. |
traction. |
||||
|
North |
o North |
East |
S.8°3 E. |
South |
S. 1° E. |
West |
S. 84iW. |
|
N. bv E. |
N. 14|E. |
E. by S. |
S.72fE. |
S. by W. |
S. 9iW. |
W. byN. |
N.84JW. |
|
N.N.E. |
N.26iE. |
E.S.E. |
S.61|E. |
S.S.W. |
S. 19J W. |
W.N.W. |
N. 72iW. |
|
N.E. byN. |
N. 36iE. |
S.E. by E. |
S.50fE. |
S.W.byS. |
S. 30A W. |
N.W.byW. |
N. 60^ W. |
|
N.E. |
N.49 E. |
S.E. |
S.41 E. |
S.W. |
S.41 W. |
N.W. |
N.49 W. |
|
N.E. by E. |
N. 61fE. |
S.E. by S. |
S.29JE. |
S.W.byW. |
.S.51f W. |
N.W.byN. |
N.35JW. |
|
E.N.E. |
N. 73 E. |
S.S.E. |
S. ISIE. |
W.S.W. |
S.62iW. |
N.N.W. |
N. 24 W. |
|
E. by N. |
N. 86iE. |
S.byE. |
S.lOiE. |
W.byS. |
S.72JW. |
N.byW. |
N. lUW. |
Xxvi INTRODUCTION.
exhibitiii"-, as before, the correct magnetic courses which the ship is actually steering when her l)ead is on tlie points placed against them, and to which corrected courses the variation is to be applied.
This method, by two compasses, may after all be considered as a modification of that by one ; for the compass on shore may be supposed as always in the same line between an imaginary distant object beyond it and the compass on board, at the instant of
observation.
Cases may be imagined at sea, where it might be of great importance to aship, the local attraction of which had not been measured, to obtain some near approximation to its amount. This may be often effected by taking several azimuths and amplitudes of the sun with the vessel's head on various points of the compass, and thus inferring the variation due to each of these points. It is manifest that this is only a variety of our first method, described at page xxiii., the sun being employed instead of the distant terrestrial object. Again, a ship will have a thousand opportunities when in sight of the land, of setting by the compass, some very distinct well-defined cape or peak, and of throwing her head into such a variety of positions, as to furnish very considerable data for estimating the local attraction. The maximum being generally within a point or two of East and West, it will be desirable to obtain several bearings with the vessel's head in those directions.
We have said in a former part of this paper that the directive effort on the needle, of the local attraction of the vessel, increases as she recedes from the magnetic equator towards the poles, and therefore the amount of local attraction is continually varying. No favourable opportunity should therefore be lost of ascertaining its amount in diffe- rent parts of the world. Each set of observations will suffice for a very large range of latitude, but all these observations, provided they were made with the same compass in the same place, should be preserved as affording useful materials for further investi- gation.
As connected with this not less important than interesting subject, we deem it our duty to allude here briefly to the azimuth compass, and to urge the universal adoption of a practice, which for some years has been gradually making its way in well re- gulated ships,^ — we mean the assigning to that instrument one invariable position amidships. Being fitted on a tripod stand, the legs are always placed in the same position by means of marks in the deck, the compass consequently always takes the same place. But as this compass will have its own deviation from the magnetic meri- dian, arising from local attraction, the seamen should take care to know its amount on each point as compared with the steering compass, in order to apply the variation to that compass which may result from observations with the azimuth compass ; and we cannot too strongly insist on the necessity of making all such observations originally assigned to it, J'rom that spot alone. A disregard to this important regulation is too common at sea. If the view of the sun should be impeded by a sail, or by the rigging or masts, a position somewhere else is chosen to obviate the inconvenience, instead of the sail being taken in, or the position of the ship's head somewhat altered. Hence an incorrect result is sure of being obtained, for as the local attraction changes in every part of the vessel, so the angle of variation of any one compass, at any one part of the vessel, must be compounded of the two angles which represent the real variation, and the effect of local attraction. We may also here remind the seaman that if he wants to determine the actual variation, undisturbed by the magnetic action of the vessel, he must lay her head on the magnetic meridian or line of no attraction. The important discovery of Professor Barlow, that the influence of iron bodies on the magnetic needle lies entirely in their surfaces, was followed by his ingenious plan of neutralizing
INTRODUCTION.
XXVll
their effects on the compass, by means of a thin iron disc, known by the name of Barlow's Correcting Plate.
We will now describe the mode recommended by the professor, of applying this im- portant acquisition to ships navigating high northern or southern latitudes, where the effect of the deviating power on the needle is so much increased by the great distance from the magnetic equator. From a small code of instructions which accompany the plate we extract the following examples of finding the local attraction. They are similar to those which we have already explained ; but as they are referred to in the directions for fixing the plate, we take them accordingly.
" Observations on the hearing of a distant object in H.M.S. Isabella, ivith a view of ascertaining the amount of her local Attraction.
|
Direction of |
Bearing of |
Local |
Direction of |
Bearing of |
|
|
Ship's Head. |
Object. |
Attraction. |
Ship's Head. |
Object. |
Attraction. |
|
North |
N. 51 26 W. |
o / —1 36 |
South |
N. 47 56 W. |
o / 4-1 54 |
|
N.byE. |
50 26 |
—0 36 |
S. by W. |
48 26 |
XI 24 |
|
N.N.E. |
49 41 |
+ 0 9 |
s.s.w. |
50 0 |
—0 13 |
|
N.E.byN. |
48 41 |
+ 1 9 |
S.W. by S. |
50 26 |
—0 36 |
|
N.E. |
47 51 |
+ 1 59 |
S.W. |
51 11 |
—1 21 |
|
N.E. by E. |
46 56 |
+ 2 54 |
S.W. by W. |
52 56 |
—3 6 |
|
E.N.E. |
46 26 |
+ 3 24 |
w.s.w. |
53 56 |
—3 6 |
|
E.byN. |
45 56 |
+ 3 54 |
W.byS. |
54 11 |
—4 21 |
|
East. |
45 26 |
+4 24 |
West. |
55 11 |
—5 21 |
|
E.byS. |
44 26 |
+ 5 24 |
W.byN. |
55 41 |
—5 51 |
|
E.S.E. |
44 26 |
+ 5 24 |
W.N.W. |
55 46 |
—5 56 |
|
S.E.byE. |
44 26 |
+ 5 24 |
N.W. by W. |
55 46 |
—5 56 |
|
S.E. |
45 1 |
+ 4 49 |
N.W. |
55 11 |
—5 21 |
|
S.E.byS. |
45 36 |
+ 4 14 |
N.W. by N. |
54 26 |
—4 36 |
|
S.S.E. |
46 26 |
+ 3 24 |
N.N.W. |
53 26 |
—3 36 |
|
S. byE. |
41 56 |
+ 2 54 |
N. by W. |
52 26 |
—2 36 |
"The following is an example of observations made according to the second method, on board H.M.S. Hecla, Captain Parry, May 8th, 1824:
" Local Attraction of H.M.S. Hecla.
|
Direction of Ship's |
BeariDg |
of Ship, |
Bearing from Ship, Station of Ship. |
Local |
Direction of Ship's |
Bearing |
of Ship, |
Bearing from Ship, Station of Ship. |
Local |
|
|
Head. |
Station from Ship. |
Attraction. |
Head. |
Station from Ship. |
Attraction. |
|||||
|
s. |
E. |
N. W. |
S. |
E. |
N. W. |
|||||
|
North |
41° |
0' |
40° 50' |
+ 0° |
10' |
South |
37° |
0' |
36° 58' |
+ 0° 2' |
|
N. by E. |
42 |
20 |
43 54 |
—1 |
34 |
S.byW. |
||||
|
N.N.E. |
42 |
0 |
45 51 |
—3 |
51 |
S.S.W. |
38 |
30 |
34 53 |
+ 3 32 |
|
N.E.byN. |
S. W.byS. |
|||||||||
|
N.E. |
46 |
0 |
50 38 |
—4 |
38 |
S.W. |
42 |
20 |
36 30 |
+ 5 50 |
|
N.E. by E. |
44 |
10 |
50 36 |
—6 |
26 |
S.W. by W. |
44 |
0 |
38 30 |
+ 5 30 |
|
E.N.E. |
43 |
10 |
49 33 |
—6 |
23 |
W.S.W. |
46 |
10 |
39 46 |
+ 6 24 |
|
E.byN. |
40 |
50 |
47 29 |
—6 |
39 |
W. by S. |
47 |
20 |
40 48 |
+ 6 32 |
|
East |
30 |
56 |
43 28 |
—6 |
38 |
West |
47 |
0 |
41 29 |
+ 6 11 |
|
E.byS. |
34 |
0 |
40 59 |
—6 |
59 |
W.byN. |
49 |
0 |
41 10 |
+ 7 50 |
|
E.S.E. |
30 |
20 |
37 23 |
—7 |
3 |
W.N.W. |
49 |
50 |
42 49 |
+ 6 51 |
|
S.E.byE. |
28 |
0 |
33 39 |
—5 |
39 |
N.W. by W. |
49 |
40 |
42 58 |
+ 5 42 |
|
S.E. |
25 |
40 |
30 24 |
—4 |
44 |
N.W. |
49 |
0 |
43 52 |
+ 5 8 |
|
S.E. by S. |
27 |
50 |
31 1 |
—3 |
11 |
N.W. by N. |
47 |
0 |
43 24 |
+ 3 38 |
|
SS.E. |
29 |
40 |
32 0 |
—2 |
20 |
N.N.W. |
45 |
30 |
42 44 |
+ 2 46 |
|
S. by E. |
30 |
0 |
31 30 |
—1 |
30 |
N.byW. |
43 |
10 |
41 36 |
+ 1 34 |
e2
Xx\m INTRODUCTION.
" 3Iet/iod of fixing the Plate.
" The local attraction being determined by either of the above methods, take the mean of the two deviations when the line of no attraction is N.E. and N.W. the mean of the two at East and West, and the mean of the two at S.E. and S.W.* In the pre- sent case these would be, mean at N.E. and N.W. 4° 53' ; mean at E. and W. 6° 24' mean at S.E. and S.W. 5° 17'.
" Look for three corresponding or nearest local attractions in anyone line in the fol- lowing table, filled up with written figures sent with the plate, and opposite to them, in the^first two columns, stand the proper depth and distance that the plate is to have with respect to the compass ; that is, the first column shows the depth in inches the centre of the plate is to be fixed below the pivot of the needle ; and the second, the dis- tance it is to be placed from a plumb-line falling from the centre of the needle, — observ- ing always to place it in the line of no attraction, which in the last example, and in the generality of cases, is fore and aft ; but in the first example of the Isabella, it is in a line passing from the compass, at an angle of two points, with the keel of the vessel over the larboard bow.
" In this line of no attraction, and at the depth and distance as above described, the plate may be fixed either fore or aft of the compass ; but the latter is best, particularly in northern voyages, because, when thus situated, it gives considerable freedom to the needle, and causes it to traverse where it would otherwise be useless for want of direc- tive power ; and the action of the iron being neutralized by the plate, the bearing of the needle is always correct while the latter is in its place. When it is placed before the compass, the plate is only used occasionally, its attraction is the same as the ship's, but it is in the same direction ; by applying it, therefore, at any time, the amount of the attraction may be ascertained ; but it is not neutralized as in the former case. It will of course be understood that the brass conical part, sent with the plate, is to be screwed upon the pedestal or compass-stand, to serve as a socket for the brass pin which carries the plate ; and that when the place for the plate is determined, a hole is to be drilled through the brass pin, to correspond with the hole in the socket, in which a smaller pin is inserted to keep the plate to its place."
* In the first example, as the line of no attraction is oblique to the keel or fore and aft line, the mean of the points with the line of no attraction at N.E. N.W., E. and W., and at S.E. and S.W. will be, when the ship's head is E.N.E. and N.N.W. 3° 30' ; E.S.E. and W.N.W. 5° 40' ; S.S.E. and W.S.W. 3° 15'.
{
I
INTRODUCTION.
XXIX
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Having now laid down these instructions before our readers, it is no less our duty to lay also before them the objections which have been advanced against the use of the plate.
It is held that the method proposed for the correction of the local attraction is not founded on sound principles, though possibly, in a practical point of view, where the local attraction is of so small amount, no great errors might arise from the application of the plate, so long as the vessel is on an even keel, that position in which it was originally fitted. But even in this case, if a small mass of iron, placed so near to the compass as is here required, neutralize the effect of the distant large masses in some positions of the ship, in others of necessity it must fail to do so. In some cases it must leave part of the local attraction uncorrected ; in others it must over-correct that force, producing a deviation of the needle in a direction contrary to that which the local attraction would produce. This effect would arise from the length of the needle being extremely small, as compared with the distance of the large masses ; but great, relatively to the distance of the correcting plate. Professor Christie has pointed out in the Philosophical Transactions, that in a deviation of 13° or 14° by iron, at the dis- tance of twenty-four inches, there was a difference of two, in the deviation of a needle six inches long, and that of one, in a needle one and a half inches long ; and the de- viation of this again differed from the deviation of a needle of three inches long. If the vessel heels much, the resultant of the ship's attraction and that of the plate on the needle will be considerably inclined ; and cases may therefore occur, where the correcting plate might increase the effect which it was intended to counteract.
i
XXX
INTRODUCTION.
Chronometers.
Lunar observa- tions.
CHRONOMETERS would be highly useful for the improvement of marine geo- graphy, were navigators to adopt an uniform method, by marking in their journals the Fono-itu'de obtained by these excellent machines. In taking a departure for chrono- niefors at sailing from any port or headland, the longitude alloived to that place should be marked disti'ictly in every ship's journal ; and the longitude measured from it by chronometers to every headland, island, or danger, during the passage, ought to be carefully stated ; by which means the relative meridians of those places will be obtained, and be ready to be compared with the admeasurement of the same by other
ciironometers.*
But unfortnnately, the generality of navigators seldom mention in their journals the longitude which they have allowed to the place of departure; and instead of carrying on The longitude made daily from the meridian of that place, they mark longitude from the meridian of Greenwich. The journals, therefore, are of little or no use for any future purpose, on account of the indefinite manner in which the longitude is marked.
^Yhen the longitude obtained by lunar observations is carried on daily by chrono- meters, it ought also to be marked distinctly, in order to prevent any mistake.
When lunar observations are taken, the objects on both sides of the moon ought always to be observed if possible, and the mean taken ; which will contribute to correct or modify the errorsof the instrument, particularly when the distances are nearly equal and fall on the same part of the arch of the sextant : and the difference of longitude run by log, between day and night observations, ought never to be applied in carrying on the one to the other, if there is a chronometer on board. Tf, for instance, some obser- vations of the sun and moon are taken in the afternoon for longitude, altitudes of the sun should be taken nearly at the same time to obtain the error of the chronometer, for the apparent time at ship ; having also marked down the time by chronometer when the distances of the sun and moon are observed, the error of chronometer must be applied to it, to reduce it to the apparent time of observation. When the observa- tions are taken afterwards by the moon and stars in the night, the time by chronometer ought likewise to be marked down, and its error applied, together with the loss or gain of the chronometer (proportionate to its daily rate) for the time elapsed between these observations and those taken in the afternoon by the sun and moon. The apparent time at ship when the observations of the moon and stars were takeit, will then be measured by chronometer to the meridian of the place where the observations of sun and moon were taken in the afternoon, and the mean of both should be taken for the longitude of that place, after comparing the apptrent time of observations with the Greenwich apparent time. By using the chronometer in this manner, the errors liable to arise from currents, and from the admeasurement of a ship's run by log, between day and night observations, will be avoided.!
t
• To shew the utility of this, the following example may he given. In the journals of tn-o ships, which saw the Brill Shoal and Middle Island in the Straits of Salayer, at different times, I find they had lunar ob- servations in both ships, which the journals assert may be depended upon in fixing the longitude of those places. It nevertheless happens, that the observations differ 20 miles ; for those taken in one ship make tlie BriU Shoal and Middle Island 20 miles more easterly than those of the other ship ; but having chronometers on board of both ships, they agree exactly in measuring the difference of longitude between the Brill Shoal and Middle Island, although there is a difference of 20 miles in stating the longitudes of these places by the lunar observations.
t It is very perplexing to young navigators, that nautical time, or that used at sea, is 24 hours later than astronomical time ; because the nautical almanac, and all the tables in general use, are computed for astronomical time. As the security of navigation depends upon astronomy, it certainly would be of utility to resign this irregular prejudice, and make nautical time conform to astronomical time.
INTRODUCTION. xxxi
PRECAUTIONARY REMARKS.
Conformably to the design of this work, which is the safety of lives and property, a few precautionary remarks to mariners may be introduced wliich are the result of the writer's personal observation.
CORAL SHOALS, particularly when they are white or variegated, will generally Corai shoaU. be visible from the mast-head when the sun is near the zenith, and shining bright. If the situation of the observer is between the sun and coral shoals, the latter may fre- quently be discerned, although the sun's altitude is not very great; but the glare of the sun will hide them from the observer, when they are situated between him and that luminary.*
Detached clouds, passing with a slow motion under the sun's disc, have their shadows often cast upon the surface of the sea, resembling greatly the appearance of coral shoals.
But as a general rule, it may be observed, that coral shoals are best discerned when the sky is clear, w ith the sun shining at a great altitude ; and particularly if the situa- tion of the observer be between them and the sun, with his eye considerably elevated above the surface of the sea.
Coral reefs abound chiefly within the tropics, particularly in the Indian and Pacific Oceans, and round New Holland ; many of the islands are either surrounded by these reefs or stand upon a coral base. The formation of coral reefs by zoophytes is very remarkable, as these are neither perfect animals nor vegetables, but partake of both. Most of them take root and grow up into stems, multiplying life in their branches, and in the transformation of their animated blossoms or polypes, which are endowed with spontaneous motion. Plants, therefore, resemble zoophyta, but are destitute of ani- mation and the power of locomotion ; and zoophyta are, as it were, plants, but furnished with sensation and the organs of spontaneous motion. Of these some are soft and naked, and others are covered with a hard shell ; and it is astonishing with what rapidity they form coral reefs, by taking root often at the bottom of the sea in deep water, whence the stems branch upward, and gradually but speedily, become transformed into solid rock. As these concretions of coral grow up near the surface of the sea, they become dangerous to ships ; and after they appear above it, they are gradually transmuted into islands of various dimensions, according to the extent of their original basis.
Ships which stop on the East coast of Madagascar, at Cape Negrais, Tavay, Nico- Unheaith) bars, Poolo Bay, Batavia, Borneo, or at any place within the tropics, where the country p'*"*' is low, woody, uncultivated, and considered unhealthy, ought not to allow any of their people to remain on shore during the night, when wooding and watering at such
* There is a little instrument, recently brought into use for the express purpose of discovering shoals under these circumstances. It consists simply of a piece of tourmaline, set in a small tube, for the convenience of ^
applying it to the eye, — the tourmaline having the property of neutralizing the glaring effects of the sun's rays. V
xxxu
INTRODUCTION.
Swimming.
On stowage to prevent ships from labouring in stormy wea. ther.
places : nor should they be sent on shore in the mornings, until the noxious vapours are dispersed, by the influence of the sun penetrating into the forests.
Persons who have not learned to swim, when they fall into the sea by accident, often drown themselves by lifting their hands above the surface, with a rapid and irre"-ular motion. With proper resolution this may be avoided, for a, gentle and slow motion of the hands U7ider the surface of the water, either obliquelij ov perpendicularly , like the feet of a dog when swimming, will be sufficient to keep the face of any person above the service, if there is no broken water. This will be more obvious, when it is generally known that the specifiic gravity of the human body is commonli/ lighter than sea water, as many persons float on the surface of the sea without any motion.
The natural position for persons to float in, is on their backs, with their arms, whicli act as levers, extended close under the surface, to preserve them in the natural position. If a person floating on his back place his arms close to his side or across his breast, he will soon be changed from the horizontal position, for his feet will descend perpendicularly, and then his mouth and nose will gradually be iramerged under the surface. If in floating, his arms are extended perpendicularly from his body, he will generally remain in the natural position a considerable time before his feet begin to descend from the horizontal to the vertical position. If his arms are extended beyond his head, with the palms of his hands spread just under the surface of the water, he will float steadily in the horizontal position, with his face above the water, and his toes touching tlie surface. In this manner the author has frequently floated, in warm climates, half an hour at a time without the least motion, and generally was inclined to sleep : by placing the arms a little forward or backwuid the natural floating position is always adjusted to the greatest degree of regularity. It ought, however, to be observed, that the specific gravity of some persons is rather heavier than sea water, and such persons cannot float with their faces above the surface for any considerable time without employing a little motion with their feet.
When ships are chiefly laden with dead iveight, such as iron, lead, zinc, &c., they labour and roll greatly ; to modify which, part of the dead weight is generally placed high in the hold, or between the decks. This, however, has little effect in retarding the quick rolling motion, which frequently endangers the masts when there is much swell ; for the dead weight being placed over the whole breadth of ships acts as a pendulum on the sides, to augment the rolling motion. Returning from China, in the Anna, by the eastern passage, laden deeply with sugar and tuthenag, we had a gale of wind near the Pellew Islands in which the ship rolled very quick, broke some of the rigging and the foretopmast. In order to prevent this quick and dangerous rolling, tuthenag was taken from the hold, and placed in great quantities upon the decks, until the ship had scarcely stability left to carry proper sail ; notwithstanding, there was very little diminution of her rolling.
Were it possible to compress all the dead weight contained in a ship into a ball, and then to place it at the centre of motion, she would in such case roll very little, because there would be no heavy weight near her extreme breadth. But as this cannot be done, an approximation seems desirable, which may be effected by stowing all the light goods along the sides and at the extremities, and the heavy articles in a longitudinal section over, and on each side of the keel, from the fore to the after hatchway, as cir- cumstances require; and the dead weight may be carried up to the deck in this manner.
INTRODUCTION. XXXlll
or to any height consistent with the stability of the ship. This method was adopted in loading the Anna, when a great proportion of her cargo was iron, and she was very easy during the passage from London to Bombay ; for the light goods being placed at the extremities and in tivo sections along the sides of the ship, the cause of her pitching and rolling, was thereby greatly limited.*
EXPLANATORY REMARKS.
Explanatory remarks are here necessary, on account of the ambiguous terms applied On the com. in common language to the direction of the winds, waves, and currents. "^^ei wTheX
The point from which the wind proceeds usually gives it its name: when the wind ruction of
T- *^ IV 1 nils w 'IVGS
\)\o\\Bjrom the North, it is called a North wind, and vice versa. This order, however, currents, &c. ' seems to have been sometimes reversed by navigators ; in the early voyages of the Por- tuguese to India, the wind that blows from N.E. is in some journals called the S.W. monsoon; and that which blows _/)owj S.W. is called the N.E. monsoon; thereby, taking the name of the place to which the wind is proceeding.
The terms used by navigators to signify the direction of the waves, are also very vague and undefined; for although, like the wind, the waves generally receive the name of the direction /row which they proceed, the waves or swell running from North to South being called a northerly swell, and in like manner for those running in any other direction; this is not always the case; as the waves or swell running from North to South, is called in some journals a southerly swell.
The terms applied to the direction of currents, are generally the reverse of those used to denote the direction of the wind and waves ; as the direction to which the current is going commonly gives it its name ; so that a current running from North to South is almost uniformly called a southerly current, and that running from East to West, a westerly current. Some navigators, however, have been disposed to reverse this order ; for one of our circumnavigators, in his voyage to the South Sea, calls a cur- rent running from East to West, an easterly current, and vice versa.
From the indefinite mode, therefore, in use amongst navigators, of marking the direc- tion of the winds, waves, and currents, it seems necessary to state in what manner these terms of direction are applied throughout this work.
The direction of the wind is named according to the point^Vom which it blows. Terms how
The direction of the waves, swell, or sea, is named according to the ^o\nt from work." '"^ whence they proceed.
The direction of the current is named according to the point to which it is running, if not otherwise expressed.
The course steered by a ship, signifies her course by comjmss, or magnetic.
All the bearings are by comjtass, if not otherwise expressed.
THE GEOGRAPHICAL POSITIONS of the pma>aZ places mentioned in this pinnsadopted
to secure per- j. ■ 1 1- 1 1 ... ., . spicuity and
* Articles liable to ignition, such as oil of vitriol, paint, oil, &c., ought not to be stowed below, but if pos- faciliiy of re. sible should be placed in a safe place above the decks, in order to prevent the risk of fire. Even coal has been ference. found subject to spontaneous ignition at times, which was experienced at Calcutta in October 1832, on board the ship London, after her arrival from England. She had received from a collier in the River Thames about 300 tons of pyritous coal, from which a quantity of smoke was perceived to issue, and a portion of it to have ignited, producing a blue flame when water was poured on the red-hot mass. After removing these ignited coals from the hold, one of the pillars of the lower deck beams was found to be nearly burnt through. The Lord Hungerford, the same season, in the Bay of Bengal, only escaped destruction by deluging her hold with water, as coals of the same kind had ignited also in this ship.
f
Xxxiv INTRODUCTION.
Avork are stated. The names of the Ports, Headlands, Islands, and Dangers, with which the paragraphs generally commence, have been set forth in capitals, in order to render them more conspicuous, and that navigators may not be liable to lose time in searching for anyplace of which the description is required ; because it frequently hap- pens in critical situations at sea, that a small loss of time may occasion considerable danger. To facilitate the same object, side notes have been added, which will be found contiguous to, or fronting, the principal matter contained in each paragraph. And to accomplish this object in the highest degree, a copious general index is placed at the end of each volume.
ENGLAND TOWARDS INDIA.
TOWARDS MADEIRA; PLACES OF SHELTER NEAR THIS ROUTE.
THE LIZARD POINT, being in lat. 49° 57|' N., Ion. 5° 12' W., and CAPE Lizard Point FINISTERRE the westernmost promontory of Spain in lat. 42° 54' N., Ion. 9° 17' ''^^„^Zl. W., when clear of the Channel, if the wind continue fair, steer to pass to the westward of Cape Finisterre, at 20, 40, or 50 leagues distance. If the wind prevail at West or AV.S.W., pass round the Cape as near as prudence admits, then stand to the south- ward, and do not lose time by endeavouring to pass it at a great distance ; for the wind will probably become more favourable in proceeding southward, and in winter it is a great advantage to get out of the cold weather as soon as possible.
If the projecting part of the French coast, at the entrance of the Channel happen to be approached, it is proper to observe, that Ushant Light is in lat. 48° 28' 21" N., and Ushant. in Ion. 5° 3' 19" W. The soundings near Ushant are 64 and 65 fathoms : — high water Tides. about 4^ hours on full and change of the moon. Variation of the compass about 26^° W. (1828).
in the Bay of Biscay, and to the westward of Ushant, the current sets to the west- Currents near ward at times in winter ; but in summer, it generally sets N.E. and easterly. It is and*Ba*y of often found to set eastward from March to Novemljer, particularly when westerly Biscay. winds prevail ; and off Cape Finisterre, and near the South part of the Bay, it sets mostly along the Coast to the eastward ; and along the East side of the Bay it sets to the northward, parallel to the West Coast of France.* Caution is therefore requisite with a westerly wind, in standing to the southward, to weather Cape Finisterre : for with a ship's position not correctly ascertained, it would be imprudent in cloudy weather to stand to the southward in the night, if not certain of being well to the westward of the Cape.f
* Major Rennell, im his investigation of the Currents of the Atlantic Ocean, says, that a branch of the North African or Guinea Current " passes into the Southern part of the Bay of Biscay, and after coasting the Northern shore of Spain, turns to the N. and N. W. along the coast of France ; and shooting across the mouth of the English and Irish Channels, bends round to the W., and thence through all the intermediate points to the S.E. ; and falling again into the original current, performs a complete rotation between Spain, France, and the Atlantic at large. It is the outer or N. E. side of this vortex, which, by a kind of centrifugal motion, flies off to the N. W. and across the two Channels, and forms the current which so often places ships in danger near Scilly."
f A deplorable example of Jhis, was experienced by his Majesty's ship Apollo, with a fleet of 69 ships under convoy for the West Indies. Having sailed from the Cove of Cork, March 26, 1804, with a fair wind blowing strong, they steered about W. S. W. till the 31st, the wind then came more to the westward. At noon, April 1, the observed lat. 40° 51' N., Ion. 12° 29' W., by account. At 8 p. m. the wind shifted to S. W. and increased
B
BAY OF BISCAY.
N. w. gales. Gales from W.N.W. sometimes blow into the Bay of Biscay, continuing for several days, and some of the outward-bound East-India ships have been driven far into the Bay during these gales in April and May. if a ship have the misfortune to lose any of her masts during one of these gales, the heavy sea rolling in from N.W. and W.N.W. with an easterly current, would unavoidably force her to leeward ; and should the gale continue long and severe, she might be in danger of drifting on a lee-shore. It may therefore be expedient to give a brief description of places in tlie Bay of Biscay which are sheltered from gales at N.W. or W.N.W.
BELLE-ILE and BASQUE ROAD are the places which afford the best shelter for large ships in westerly gales.
Beiie-Ue. BELLE-ILE is about 10 miles long from N.W. to S.E., and 5 miles broad, and lies
between the parallels of 47° 24' and 47° 16' N., and being high may be seen at a great distance. The N.W. end is surrounded with rocl:s, and nearly in the line between it and He Grouais, mid-way between them, is the Birvideaux Bank. A ship approaching the island with the wind at N.W. or W.N.W., should steer along the South side at 2 miles distance, to Point du Canon, the S.E. extremity ; and when abreast of this point, haul up for Point Kerdonis, called in some of our charts Point Loc-maria, which is the easternmost point of the island, distant about 2 miles from the former, anchoring under it in 8, 10, or 15 fathoms, where she will be sheltered from N.W. and westerly winds. If the wind should veer to S. W., she may run to the northward of the point and anchor on the N.E. side of the island. — There is now a revolving light near the S.W. part of the island, in lat. 47° 18' 40" N., and Ion. 3° 1.3' 31" W.
He Hedic. ILE HEDIC, about 7 miles eastward of Belle-He, is, with its contiguous dangers,
the termination of the rocky range which stretches S.E. from the peninsula of Quiberon. Near the East point of the island there is a small fixed light, whicli may be seen, in clear weather, about 3 leagues. Off the S.E. end of the island lies a cluster of rocks, called the Cardinals : the largest is distant from Hedic about a mile, and is always above water. If a ship be driven to the eastward of Belle-He, she may pass to the southward of the Cardinals a mile distant, then haul up to the northward, and anchor on the East side of them and He Hedic, in 9 or 10 fathoms, sand and mud.
iieR^, &c. Ships bound to Rochelle, or Rochefort, steer for He Re, which has a lighthouse on
its N.W. end, in lat. 46° 14' 44" N., Ion. 1° 33' 35" W. In running for this island, care is requisite to avoid two reefs of rocks, on which the sea sometimes breaks, called the Banche Verte, and Roche Bonne : they are nearly 2 leagues in extent S.E. and N.W., distant about 12 leagues West from He Re, in about lat. 4(3° 12' N. Near them to the westward there are 60 fathoms water, and 30 fathoms to the eastward of them. From the West point of He Re, a rocky bank, called Les Baleines, extends under water about a league; and from the S.W. part of the island a ridge of rocks,
shotf'" called Chanchardon, extends a full league to seaward; but the Lavardin Shoal is
to a gale with a heavy sea; they stood S. S. eastward, and at half-past 3 on the following morning struck on the coast of Portugal, in lat. about 40° 22' N., 3 leagues northward from Cape Mondego. A few sights obtained, for even an indifferent chronometer, on the day preceding this fatal catastrophe, when the sun was visible, or by stars m the night, would have prevented this deplorable loss of lives and immense property ! No ship should be without two or three chronometers.
COAST OF SPAIN. 3
most in the way. It is a small rocky bank, dry at low-water spring-tides, about H miles off the S.E. end of He Re. He Oleron lies to the South of He Re, and between them is a channel, about 2 leagues wide, called Pertuis d'Antioche, leading to Basque Road. It is safer to keep nearer He Re than Oleron, on account of some rocky banks, called the Antioches, which lie half a league off the North end of the latter, and which bank.s extend about the same distance from the shore along its N.E. side till abreast of the South end of He d'Aix. When near the S.E. end of He Re steer to the southward, to avoid the Lavardin Shoal already mentioned, lying ]| or 2 miles off the S.E. end of He Re ; afterwards steer for the West part of He d'Aix, a flat island, with some houses on it, situated about half-way between Oleron and the main land, keeping nearer Oleron than the main.
BASQUE ROAD extends from the Lavardin Shr,al to He d'Aix, having from 10 Basque Road. fathoms water close to the shoal, to 12 and 1.3 fathoms in the middle of the road ; and from 5 to 9 fathoms about 1^ miles to the North and N.W. of He d'Aix. The sound- ings in mid-channel, between Oleron to the southward and He Re and Lavardin Shoal to the northward, are generally from 12 to 1-5 fathoms, shoaling on each side toward the banks. On the northern extremity of Oleron, there is a lighthouse-tower, called Chassiron, shewing a fixed light, in hit. 46° 2' 51" N., and Ion. 1° 24' 29" W. If there be much sea in Basque Road, a ship may run up along the West side of He d'Aix, taking care to keep nearer to it than to Oleron, to avoid the bank off the latter ; and then anchor in 5 or 6 fathoms, off the S.W. end of Isle d'Aix, in the inner road. There is S, small fixed light on the fort near the point.
BAYONNE and BILBAO are confined harbours, and have not sufficient water for Bayonncand large ships over the bars at their entrances. Vessels should not attempt to enter them ^'"""'• without a pilot.
THE COASTS OF PORTUGAL AND SPAIN having been sometimes visited by coastsof Por. India ships, when forced by stormy weather to take shelter in some of the nearest ports s"^j||,''"'* in order to repair damage sustained, it may therefore be useful to describe briefly some of the principal headlands and best harbours on the western side of the Peninsula.
CAPE ORTEGAL, the northernmost headland of Spain, is in lat. 4.3° 48' N., Ion. 7° capes oncgni 46' W. ; and about 12 leagues to the south-westward of it, is Cape Prior, in lat. 43° 35' N., "'"' ^'"'"• having a very ragged aspect, with some rocks near it, which require a berth in passing. This Cape is above 2 leagues to the N.W. of the entrance into Ferrol, and between 4 and 5 leagues from the Iron tower, or lighthouse of the Groin, or Coruiia.
FERROL BAY, which forms the entrance to its harbour, is 7 miles to the southward i l""'- of Cape Prior, and is a mile wide, narrowing gradually till it terminates in a channel not more than 2 cables across, which leads to the harbour, and which has sufiicient deptli of water in mid-channel for large ships at all times of tide.
When a vessel comes near the Bay of Ferrol, the haven begins to open, and you sail in mid-channel between two headlands ; but when within, steer to the northward and anchor by the North point, for it is rocky and fiat on the West side of the town, and therefore must be avoided.
B 2
COAST OF PORTUGAL.
Corufia.
Salvora Isle, and Arosa Bay.
OnzA Isles, and Ponteve- dra Bay.
To enter Ferrol from the southward or westward (after giving a berth to the North point of Ferrol, wliich is foul and rocky until the haven opens), run right in, and you will be within the South point, clear of its projecting foul ground ; steer now for the INorth i)oint of the haven, and along by it, till the haven opens itself again ; from thence keep in mid-channel, where are 12, 14, and 15 fathoms water, though the passage is so narrow that a stone may be thrown across it.
CORUNA is situated at the bottom of a deep bay, within the mouth of a spacious haven, S.W. of Ferrol, and on the opposite side of the gulf. To enter this port, havinjr made the Sizarga Islands, which being foul must have a good berth, steer for the remarkable lighthouse called the Tower of Hercules, and run in E.S.E., and round the point steering S.E. and S.S.E., giving it a berth of 4 or 5 cables-lengths. In passing the point, the small Isle of St. Antonio will be seen with a castle on it, round which a ship may sail very close, and anchor oft" the Fishing Village in G, 7, or 8 fathoms.
Vigo Bay and Bayona Isles.
Cape Mon- dego.
Cape Car- voeiro.
Burlings and Estellas.
SALVORA ISLE, in lat. 42° 28° N., fronts the bay or gulf of Arosa, which is a deep and excellent haven, extending from the Isle about N.E. a great way inland, having good shelter and moderate depths, with several shoals. The channel into this bay is on the South and East side of Salvora Isle, where a ship is sheltered inside the Isle ; but there is no safe passage on the N.W. side of this Isle, it being nearly joined to the main by shoals.
THE ONZA ISLES, situated oft" the inlet of Pontevedra, have on the East side safe anchorage from westerly winds. They are two in number, and extend about four miles from North to South. The northern one, which is much the larger, is called 0ns, the southern one Onza. The South point of the latter is in lat. 42° 2 1' N., oft" which, at the distance of half a mile, there is a rocky shoal on which the sea breaks in rough weather. Fresh water may be procured at these Islands.
VIGO, in lat. 42° 14' N., Ion. 8° 27 VV., is situated on the S.E. side of an excellent bay or haven, which is fronted by the Bayona Isles, extending from lat. 42° 11' N. to 42° 15' N., and on the East side of these Isles, there is safe anchorage and shelter from the sea and from westerly winds, in 10 and 12 fathoms. The best channel into Vigo Bay, is to the South of these Isles ; for the northernmost Isle has a sunken rock about a cable's-length oft", which must have a proper berth in entering by the northern channel. When entering the bay, run up in mid-channel, and anchor in 10 or 12 fathoms off Vigo; or farther in, about Point Rondal, where a ship, if destitute of anchors, may be laid in the mud and receive no injury.
CAPE MONDEGO, in lat. 40° 1 1' N., Ion. 8° 53' W., is a projecting headland on the coast of Portugal, with a reef stretching out about a cable's-length, having good anchorage and shelter on the South side from North and N.N.W. winds.
CAPE CARVOEIRO, in lat. 39° 22' N., Ion. 9° 24' W., is a rocky headland, with a lighthouse like a church on its extremity, and being separated by a low sandy isthmus from the inland country, it appears in thick weaUier like an island, by which some ships, mistaking it for the Burlings, have run on shore on the sandy isthmus.
BURLING ISLAND, in lat. 39° 25' N., is of middling height and size, bearing from
RIVER TAG US. 5
Cape Carvoeiro, N.W. by N., distant G miles nearly. N.W. of the Burlinjr, ^ a mile distant, lie six islets, called the Estellas, in an E.N.E. and W.S.W. line, with a rock about ^ mile to the southward of the southernmost one, visible at low water ; there is also a high rock at a small distance N.E. of the Burling.
FARILHAOS, are a cluster of small islets and rocks, 4 miles north of the Burling. Fariihaos. There is a safe channel, about 3 miles wide, between this aroup and the Estellas; but as the current sets toward the latter, it should not be used without a commanding breeze.
The channel between Cape Carvoeiro and Burling Island, being 5^ miles wide, vvith soundings, may be navigated without fear of danger, and a ship may anchor occasionally under the Burlings.
CAPE ROCA is formed of steep cliffs, with a rocky islet adjoining it, termed ^^p« ''"'^a. by seamen the Rock of Lisbon, from which a reef projects about a musket shot, having 25 fathoms water close to. On the summit of the Cape is a Tower, in lat. 38" 46' 30" N., Ion. 9" 30' W., on which a fixed light is exhibited. Cape Razo is a low rocky point, distant 4 miles S. by W. from Cape Roca, having on it Fort Sanxete, or Sinchette, and adjoining it a small shoal. About ^ a league S. E. by S. from Cape Razo is the fort and lighthouse of Guia, and a mile farther to the east- ward are the Forts Santa Martha and Cascaes. Round the point on which they stand, the coast bends to the northward, forming Cascaes Bay ; on the West side of which is the town of Cascaes, where pilots may be obtained for the Tagus. Fort St. Julian, at the entrance of the River, bears from Fort Santa Martha E. by S., distant 4^ miles.
THE RIVER TAGUS at its entrance is about 2|- miles wide, between Fort St. River xagus. Julian and the low sandy point of the south-eastern shore. The Channel is, however, contracted to less than a mile in width, by the two sand-banks, called the North and South Cachops, on the latter of which stands the Bugio fort and lighthouse.
Fort St. Julian stands on a steep point, having a tower 120 feet high in the centre of the fort, which serves for a lighthouse. From St. Julian to the tower of Belem the distance is five miles E. byS.; and the coast between them forms a bay with numerous edifices, some of which, situated about the middle of the bay, serve as marks for the Great Bar, or principal entrance.
The North Cachop extends about 3 miles to the south-westward of Fort St. Julian, and the sea breaks on it vvith a westerly wind. The channel between this bank and the North shore is called the Corridor or Little Bar, having 5 and 6 fathoms water, but being narrow can only be used with a fair wind.
The South Cachop is a sand-bank, having on it the tower of Bugio, formed of two circular concentric buildings, on the middle of wliich rises a little tower, 63 feet high, from which is exhibited a revolving light, bearing from St. Julian S. S. E. f E., distant t^ miles. The tower is isolated by the sand being covered every tide, and the bank extends from it 2 miles to the S.W. The Great Bar is formed between the The Bar and outer points of the North and South Cachops, and has on it a depth from 5^ to 10 '"""' ' fathoms. The channel is no where less than f of a mile wide, with from 10 to 18 fathoms good bottom ; a bank stretches across between the Cachops, having not less than 8 or 9 fathoms on it, and increasing to 15 and 20 fathoms inside. The water shoals suddenly to both the Cachops, having 6 or 7 fathoms close to.
To cross the Great Bar with a fair wind, the leading marks should be brought on Toenterthe before the meridian of Cascaes is passed, or by bringing Cape Roca lighthouse on '^"'" with that of Guia, which will be sufficiently to the westward of the Cachops till the
PASSAGE TO MADEIRA.
Tides.
Lisbon Obser- TStory.
Paijs* be discerned ; these must be brought in one with Jacob's Ladder,! and so kept until the Tower of'St. Julian bear W.N.VV. or West, when the North shore of the river may be naviijated to tiie anchorage of Belem.
If, wiien near the bar, a strong westerly wind prevent pilots from getting on board, or if the marks be not clearly discerned, do not pass the meridian of Cascaes till Belem Tower be brought on with the North end of the outer wall of Bugio, bearing E. I N. Steer on this bearing till the Tower of St. Julian bear N.E. ; being then in mid- channel, steer for the Turret of Caxias, which bears E.N.E. ; keep this course till abreast of Paco d'Arcos, then coast the northern shore to Belem.
If the Miiante or Turret of Caxias be not seen, then, as soon as the tower of St. Julian bears N.E., you will be 2^ miles from Bugio, for which steer no longer, but steer midway between St. Julian and Bugio, or so as to make good an E.N.E. course until past the bar.
The North shore of the river is the safer of the two to approach, the anchorage being better, the depths less, and the tides not so strong as near the South shore. During the freshes, the ebb tide runs frequently 6 miles an hour in the channel, requiring a press of sail to stem it, and at such times, when westerly winds blow strong, the sea breaks all across the bar between the Cachops, and cannot be easily distinguished from the breakers on the Cachops. It is high water on the bar at 2^ hours on full and change of the moon.
The observatory of Lisbon is in lat. 38° 42' 40" N., Ion. 9° 8' 30" W.
Passage to Ma. After Icaviug the English Channel, steer to pass the island of Madeira, at any **""• convenient distance exceeding 7 or 8 leagues. In the winter months, it is preferable
to pass to the westward, for strong westerly gales prevail in November, December, and January, producing eddy winds and severe squalls near the land, occasioned by Westerly gales, the high land obstructing the regular course of these gales. In November 1797 and December 1799, I was forced to put to sea from Funchal Road. Severe westerly and S.W. gales, with hard squalls and rain, kept us at sea eight days each time, and pre- vented us from anchoring afterwards; the W.S.W. wind continuing to blow strong. In these gales, the island of Madeira and the Desertas were frequently obscured in fog; and the squalls so sudden and violent near the latter, and about the S.E. end of the former, as nearly to overset one of the ships in company. J
* Two little mounts, about 2 miles N. by E. of Belem Tower, which are visible at a great distance.
t Seven walls or causeways, built to support the soil on the S. E. declivity of a round hill of yellow colour near the sea, 260 feet high. On the top of this hill is a turret, called Caxias, 3 miles E. J N. from St. Juhan, formed of two octagonal structures conjoined, each 33 feet high, and terminated in a cupola of similar shape. A good mark for Jacob's Ladder is a long wall near it to the eastward, the buttresses of which, on the side of the Tagus, appear like the arches of a bridge.
I November 28, 1797, blowing hard at S.W. off the S.W. end of Madeira, and a high sea rising, we bore away in the Carron, to endeavour to find shelter under the lee of the island. In running between Madeira and the Desertas, blowing very hard at S. W. with dark weather and rain, we were suddenly becalmed ; then fol- lowed an eddy wind from N. E., the sea so high as frequently to cover the bowsprit and jib-boom. At this time we were much nearer to Madeira than to the Desertas, with a dark cloud extending over us. At the same time, two ships about 2 or 3 miles more eastward, were in clear sunshine, running before a severe squall at S. W. ; and one of them had her main topsail blown away. In December 1799, by carrying a press of sail on the Anna, we just cleared the southernmost Deserta, in very thick weather, during one of these westerly storms, which drove us 2° eastward from Funchal. Several outward-bound West India ships were not long ago dashed in pieces on the Desertas in the night, by an error in their reckoning.
r
PORTO SANTO. — DESERTAS. — MADEIRA. 7
PORTO SANTO is a high island with several peaked hills on it, about 12 or 14 PonoSamo. leagues north-eastward from the East end of Madeira, and is generally seen by ships bound for the latter : it is surrounded by several small islands, and has a bay and small town on the south side, with anchorage, water, and refresliments. There is a small island oft" each of the points which form the bay. Although Porto Santo is not so high as Madeira, it may be seen 12 or 14 leagues from a ship's deck ; and is easily distinguished from Madeira or the Desertas, by its peaks and uneven appearance, these islands having a more regular outline. Tiie village on the S,W. side is, by Capt. Owen's survey, in lat. 33°V N., Ion. 16° 18|'W.
The existence of the danger called the Eig/it Stones, to which several positions Eight sio„es. North of Madeira have been assigned, between the parallels of 34° and 35° and the meridians of 16° and 17°, appears to be extremely doubtful; many of H. M. vessels having by Admiralty order passed over the spot, with the express object of discovering them, but hitherto in vain.
The Reef said to lie 3 leagues to the N.E. of Porto Santo, on which a Dutch ship Dutci. shoai or was lost, has been found by H. M. S. Falcon to bear about N. 18° W., true bearing, ^^^^'°" ''"^'''■ from the body of the island, distant from the nearest point about 5 miles.
The Falcon, Lieutenant J. Bowen, examined this reef, or rocky bank, on the 10th of January, 1802. It extends East and West about a mile, terminating in a point of rocks to the westward, on which the least water appeared to be 4^ fathoms. Lieutenant Bowen remarks, that when the bearings were taken upon it in the boat, the compass was agitated by her motion, and therefore they may not be perfectly correct; but he is certain that the boat was on the shoalest part, otherwise the sea must have broke on it had there been less water, by the considerable swell and fresh breeze which prevailed at the time. Coming on to blow, he was prevented from making further observations.
With the wind from the northward or N.E., bound to Fuuchal, the channel between Madeira and the Desertas is the most convenient, and seems about 4 leagues wide from the East point of Madeira to the Flat or Table Deserta, which bounds it to the eastward.
THE DESERTAS are three high barren islands, the northernmost being much Deserws. lower than the others and level. The middle Deserta is the largest, between which and the southernmost, called Bogia, there is a narrow channel, never to be attempted unless from necessity, as a ship is liable to be becalmed in it by the northern Deserta, which over-tops Bogia. The fleet under convoy of H. M. S. Lavinia, bound to India, and to touch at Funchal, passed through the channel between the Middle and South Desertas, in May 1809. They mistook the Desertas for Madeira, and after steering for the South extreme of the Large or Middle Deserta, proceeded through the chan- nel between it and the southern Island ; this channel is 1 or fi miles wide at most, and seems perfectly clear of danger. None of the ships tried for soundings, but the fishermen say, that bottom may be got with 60 to 300 fathoms of line, according to the distance from either shore.
The Desertas stretch nearly North and South, and have rather an even appearance, and are about 5 leagues in extent. The northernmost small level island is seen at 5 or 6 leagues distance, just appearing above the water, and close to its North end there is a pyramidal rock, which may be mistaken for a ship under sail.
MADEIRA is very high, and is generally clouded, exceptin serene weather ; the East Madeira. point in about lat. 32° 44' N., projects in a kind of peninsula, rather low and rugged, forming to the soutliward an indentation or bay, in which soundings are said to be found
8
MADEIRA.
Prevailin winds.
Southerly gales.
Indication of them.
Directions for sailing to Fun cbal Road.
near the shore. There is a perpendicular high cliff' of majestic appearance, about 3^ PontadcSoi. leanues westward from Fiinchal, called Ponta de Sol, with a small bay to the east- ward of it, said to have anchorage in it near the shore. In westerly gales and stormy weather, Ponta de Sol {Point of' the Sim) is often ornamented with beautiful portions of rainbows, which give it a grand appearance. In summer, when the weather is settled, oft" Funchal Valley there are regular land and sea breezes ; the sea-breeze .setting in from south-westward in the forenoon, and the land-breeze coming from the shore generally about 10 o'clock at night, but sometimes not till 2 or 3 o'clock in the morning. These land-breezes do not extend above 3 or 4 miles ofl^shore. It has been said, that southerly winds never blow severely quite to the shore at Funchal ; that the south-westers or south-easters are never expected, except in January, February, and the beginning of March, and that large ships always ride them out ; whereas, it is certain, these southerly gales blow quite home to Funchal, sometimes in November and December ; and when they are apprehended, it is common for ships of every description to put to sea. These S.W. or S.E. gales are in general preceded by a swell tumbling into the road, often accompanied by gloomy weather, drizzling rain, and an unsettled breeze from the land, veering several points backward and forward very suddenly. With such indications, ships generally proceed to sea, for should it blow from the southward, it would be almost impossible to clear the shore on either tack after cutting or slipping, the anchorage being near the land. Some ships have rode out these southerly gales, but others have been driven on shore.*
Passing through the channel between Madeira and the Desertas, it is necessary to preserve a considerable distance from the land to prevent being drifted in calm weather near either, there being no anchorage. In November, 1797, the Anna drifted in a calm very near the shore to the northward of the Brazen Head, and brought up with the stream anchor in GO fathoms water, her stern not far from the rocky cliffs. After being at anchor some time, a light breeze from the land, with the help of the boats towing, enabled her to get out from this perilous situation. When a ship has advanced through the channel, and is approaching Brazen Head, she should not keep near it, in case of being becalmed, as there is no anchorage close to this steep bluff" point, which is the eastern extreme of Funchal Road.
Near this bluff" head-land, ships are frequently baffled by eddy winds and calms, and are obliged to get their boats out to tow ; it is therefore advisable not to borrow too closely to it in passing, nor to haul in for the road till nearly abreast of the town. If a ship enter the road by night, it is proper to show a light at her ensign staflT, to prevent being fired at from the forts. Working in with a land breeze, it is best to make short tacks opposite the valley, for here both the land and sea breezes prevail. The Anchorage. Loo Rock, situatcd near the shore, at the West end of the town, is a high rock with a fort on it; and the Citadel is a brown square fort on a hill, over to the N.W. part of the town. The best berth for large ships is;the Citadel a little open to the eastward of the Loo Rock, in 30 or 35 fathoms water ; the distance from the Loo Rock will then not much exceed half a mile.
With the Loo Rock and Citadel in one, bearing about N.N.E. i E., Funchal steeple N.E. ^ N., the anchorage appears equally good, in 35 fathoms stiff" ground. With the Loo Rock and Citadel in one, the ground is also good in 45 fathoms, about a mile off" the former. Farther to the westward the ground is not so good, and to the eastward the
* Not long ago, several ships at anchor in Funchal road were driven on shore, and vprecked by one of these gales. This, I think, happened in April or May. The S. W. gales are more frequent at Funchal than any other strong winds.
MADEIRA— TOWARDS THE CAPE DE VERDE ISLANDS.
bank has a sudden declivity from 50 to 55 fathoms good ground, to 100 fathoms rock, and then no ground. If south-westers are expected, wliich are frequent in winter, to anchor with the Loo and Citadel in one, or the latter, just open to the westward of the Loo, is the most convenient berth to put to sea from, or to ride out a S.W. gale. But the Citadel well open to the eastward of the Loo is the best anchorage when south- easters are expected. In coming into Funchal Road with a brisk wind, sail should be Caution, reduced in time, to prevent having too much way through the water, at the time of anchoring; and a ship should be brought up with her head to seaward, that in case any accident should prevent her bringing up, sail can be made off shore, or otherwise as most expedient. When there is the least appearance of unsettled weather, it is best to ride with a whole cable, with a slip buoy on it, in case of being obliged to cut near the end or splice, and put to sea quickly; as there would not be time to weigh the anciior, by the sudden approach of blowing weather. In light breezes and calms, it is proper to have a kedge anchor out to steady the ship, and prevent fouling the bower.
The beach is composed of shingle, and has generally a surf on it, which prevents a ship's boat from landing abreast the town; but on the N.W. side of the Loo Rock, about half a mile from the town, is the only place safe to land from a ship's boat ; the country boats are employed in vvatering, &c.
In summer, when the N.E. wind prevails, a S.W. current sets through the channel between Madeira and the Desertas. The current along the South side of Madeira and current. the Desertas mostly sets to leeward in strong gales; but at the conclusion of a gale, it sometimes changes suddenly, and sets contrary to the wind. The tides rise and fall Tides. about 9 feet in general at full and change, when it is high water at 12h. 15m, The rainy season is said to be January, February, and March ; October is also frequently a Rainy sea wet month. And when hard westerly gales blow in November, or more particularly in December, they bring with them cloudy weather and rain.
There have been instances of hurricanes blowing down through the Valley of Funchal ; storms. a condensed cloud once poured a torrent of water on the mountain at the head of the valley, which deluged many vineyards in its passage, and washed away some of the houses in the town.*
Funchal is in lat. 32° 38' 40''' N. by above 100 meridian altitudes of Stars on both sides the zenith, observed by General Sir Thomas Brisbane and Professor Rumker, in June 1821.
Dr. Tieirks, in 1822, was sent with 14 good chronometers, in H.M.S. Owen Glen- dower, for the express purpose of measuring the difference of longitude between Greenwich and Funchal. He made the longitude of the British Consul's House 16° 53' 45"' W.
Position of Funchal.
FROM MADEIRA TO THE SOUTHWARD :
SALVAGES, CANARIES, AND CAPE DE VERDE S.
On leaving Funchal, steer directly from the shore, to prevent being baffled by calms From Madeira or eddy winds under Ponta de Sol, or the Brazen Head, for vessels are liable to calms J^aJ^! ^°""'' under the hisrh land.
* The small-pox is much dreaded at Madeira ; were a ship discovered to have this distemper on board, she would be ordered to leave the port.
0
10
SALVAGES, — CANARIES.
Salvages.
Canary Is- lands.
Palma.
Departing from Madeira, or after passing it to the westward, the usual track is to the westward of the Canary and Cape de Verde Islands, at any discretional distance, or barely in sight of them, where steadier winds may be expected, than close to, or among these islands. The Britannia, outward-bound in November 1803, had W.S.W. and S.W. winds, and was several days close to the coast of Africa, in lat. 29° N. In January 1795, the Swallow, after passing in sight of the Canary Islands to the westward, had westerly winds, which carried her to the eastward of Cape de Verde Islands ; but it is preferable to pass to the westward of all these islands in August, September, October, and November more particularly: butmanynavigators, in January, February, and March, prefer the passage to the eastward of the Cape de \'erde Islands. Captain Heathorn, of the ship Claudine, homeward-bound from India, twice, in September, passed to tlie north- ward, inside of the Cape de Verde Islands, with steady southerly winds, which changed into the N.E. trade wind, when to the northward of these islands. Hence it appears, that in part of Augnst and September, southerly winds sometimes prevail between the coast of Africa and the Cape de Verde Islands ; and in the same locality, northerly winds may usually be expected in December, January, and part of February.
If a ship be bound to Tenerife, or intend to pass between the Canaries, or is laid oft" to the S.S. E. after passing Madeira, care is requisite to avoid the Salvages, which must not be approached in the night on account of the reefs and straggling rocks extending from the Fitons, the south-westernmost of these islands.
THE SALVAGE.S are in two distinct groups, distant from each other about 8 miles in a N.E. and S.W. direction, with a safe passage between them.
The north-eastern group is formed of the Great Salvage with its surrounding rocks. It is high and rocky, and may be seen at the distance of 8 or 9 leagues. The hill near the western point of the island is in lat. 30° 7' 51" N., and Ion. 15° 51' -20", according to the survey of H. M. S. Leven in 1819.
The south-western group consists of two islands, called the great and little Piton, surrounded by rocks and reefs. The little Piton is about 1^ miles to the westward of the Great Piton, and has a reef projecting beyond to the westward half a league.
THE CANARY ISLANDS are eleven in number (four of them small), extending from lat. 27° 40' to 29° 20' N., and from Ion. 13° 35' to 18° 6' W.* They are mostly high, with steep rocky shores, rendering the landing often impracticable, and they are all destitute of safe harbours for large ships. The channel between these Islands and the African Coast is about 20 leagues wide, and clear of danger.
The channels among the Canary Islands are clear of dangers, except a doubtful sunken rock, in lat. 27° 52' N., in the channel between Canary and Tenerife, about 7 leagues from the latter, and 5 leagues West from the former; which many navigators think has no existence. Several of the outward-bound ships pass between' Palma and Gomera, when laid off" to the eastward by westerly winds, or otherwise. Mean varia- tion by Capt. Vidal 20^° W.
PALMA, the north-westernmost of these Islands, 8 leagues long and 5 leagues broad, is frequently seen by the outward-bound East-India ships: being high, with a bold coast, some navigators approach it with great confidence; but several ships have
* The Surrey of these islands was commenced by Lieut. Arlett, R. N., in 1834-35, and carried forward by Capt. A. T. E. Vidal, R. N., in 1837-38. The positions here given are from this Survey.
CANARIES.
11
been nearly lost on it in dark nights, the lights on the impending mountains first showing their situation : and even in the day it is sometimes completely obscured by fog clouds. The North point is in lat. 28° 51' N., Ion. 17° 55' VV. ; the West point in lat. 28° 46' N., Ion. 18° 0' W. ; and the South point in lat. 28° 27' N., Ion. 17° 50' W. This island is said to be more subject to westerly winds and rains than any of the others.
TENERIFE is the largest and, from its magnificent Peak, the most remarkable of Tene.ife. It is
the Canary Islands. It is triangular in shape — its length from N.E. to S.VV. is 47 miles, and its greatest breadth from N.W. to S.E. 28 miles. Captain Vidal,of H.M.S. Etna, who surveyed the Canaries in 1838, and who ascended the Peak, makes its latitude 28° 17' N., and longitude 16° 39' W. Its elevation above the sea is about 12,300 feet. North extreme, lat. 28° 37' N., Ion. 16° 9' W. South Point, lat. 28° 0' N., Ion. 16° 41' W. West Point, lat. 28° 21' N., Ion. 16° 56' W.
Santa Cruz, on the S.E. side and near the N.E. end of Tenerife, is the chief town samacruz. of the Canary Islands. It is the port generally used by ships which stop at these Islands to procure refreshments. The Road, though indifferent, is one of the best in the Canaries. Ships going in should not bring any part of the town to the northward of West, or they may be becalmed by the high land under the Peak, and drifted on the rocky shore, where no bottom is found close to it with 200 fathoms line. Merchant ships and small vessels anchor to the north-eastward of the pier, off the town, in 18 and Anchorage. 20 fathoms, distant from the shore | a mile. Ships of war anchor off the northernmost fort, about j a mile distant from it, with their outer anchor in 36 fathoms, and the inner one in 15 or 18 fathoms. The Hindostan, in October 1792, at anchor in 28 fathoms dark mud, had the southernmost steeple West, the northernmost fort North, and the easternmost point E. ^ N. H. M. S. Satellite touched here, in 1827, and got no bottom at 105 fathoms, when she had the marks on formerly recommended for anchor- ing ; she steered into the West side of the bay, within three cables' lengths of the shore, and about an equal distance from the North Fort, then anchored in 38 fathoms soft ground on the edge of the bank ; and it was thought a better anchorage would be found with the southern steeple W. f N. and the northernmost fort North. The bottom being foul in many parts of the road, it is customary to buoy the cables from the ground. This road is exposed to easterly winds, but these seldom blow hard, although it has sometimes happened that ships have been driven from their anchors on shore. Santa Cruz is an excellent place for procuring a supply of cheap wines, which are of a Keireshmcms. weak quality. Vegetables are plentiful, also the fruits common in Europe, and good water is easily procured when the surf is not great on the beach. The Mole Head, Santa Cruz, is in lat. 28° 28' 13" N., and longitude 16° 14' 35" W.
Oratava, situated on the N.W. side of the island, has a very insecure Road, where Oratava. ships stop sometimes to take in wine: the anchorage is in 50 fathoms, about 1^ miles off shore, with the Peak bearing S.W., and a pilot should be kept on board. Strag- gling rocks project two or three ships' lengths from the shore, on which the sea breaks furiously; this anchorage is very dangerous in the winter months, from September to May.— Lat. of the landing-place 28° 25' N., Ion. 16° 33' W.
CANARIA or GRAND CANARY, extending from lat. 27° 45' to 28° 13' N. ; and 12 leagues S.E. of Tenerife, is nearly round, being about 11 or 12 leagues in extent; it is the best watered, and most fertile of the islands. Palmas, the chief town,
c 2
Canariu or Grand Canary.
12
CANARIES.
Gomera.
is on the N.E. side of the island ; its Road is sheltered from the N.E. by a point of the land stretching out in a peninsula, and having some rocks adjoining, — Lat. of Mole Head, by Lieut. Arlett, R.N., 28" 7' N., Ion. 15° 25' VV.
GOMERA, about 5 leagues to the S.W. from the coast of Tenerife, is 6 leagues long, and its medium breadth 3 leagues. St. Sebastian, the chief place, is in a bay on the East side, sheltered to the northward by a projecting point. North Point, lat. 28" 13' N., Ion. 17° 16' W. East Point (San Christoval), which is near Port San Sebastian, lat. 28° 6' N., Ion. 17° 6' W.
HIERRO or FERRO,* the south-westernmost of the Canary Islands, distant 10 or 11 leagues to the S.W. of Gomera, is 6 leagues long and 3 leagues broad. Puerto del Hierro, on its East side, is in lat. 27° 46' N., Ion. 17° 54' W.
Fuerteventura. FUERTEVENTURA is about 20 leagues long, and from 2 to 5 leagues broad, the S.W. point being in lat. 28° 3' N., Ion. 14° 31' W., and the North point in lat. 28° 45' N., and Ion. 13° 54' VV.
Hierro or
Ferro.
Lanzarote.
Harbours.
Puerto de Ca- vallos.
LANZAROTE, or Lancerota, about 6 leagues long and 4 leagues broad, lies to the N.E. of Fuerteventura, being separated from it by the Bocayno channel, in which is the Island Lobos, 2 leagues long and ^ a league broad, dividing the channel into two pas- sages. That between Lobos and Fuerteventura is 2 miles wide, with 5 fathoms water and good anchorage. The channel next Lanzarote is 4 miles wide, with 10 fathoms water. Oft" the north end of Lobos there is a large reef. The East Rock oft' the North end of Lanzarote is in lat. 29° 16' N., Ion. 13° 20' W.
On the S.E. side of Lanzarote are two ports within reefs, called Puerto de Naos and Puerto de Cavallos ; the former is the northern one, sheltered from N.E, by the reefs, and here vessels may refit. It has two entrances between the reefs, with only 14 feet at high water in the northern, and 17 feet in the southern entrance; the depth within is 27 to 10 feet; rise of tide 10 feet.
Puerto de Cavallos, 1 mile South of the former, has only 12 feet in the channel; and within, 17 feet.— Fort St. Gabriel at Arrecife, lat. 28° 57' N., Ion. 13° 23' W.
Graciosa. GRACIOSA, SANTA CLARA, and ALEGRANZA, are three small islands oft'
andAU'grMza. the North point of Lanzarote ; they are uninhabited and destitute of fresh water. The channel between Graciosa and Lanzarote forms the harbour of El Rio, in which the depth is 6 or 7 fathoms. The North point of Graciosa is in lat. 29° 17' N., and Ion. 13° 31' W. The centre peak of Santa Clara is in lat. 29° 18' N., and Ion. 13° 32' W. Alegranza North Point, lat. 29° 25' N., Ion. 13° 31' W.
Channel within Some outward-bound ships for India, or St. Helena, prefer the channel between
VerSTsiands. Cape de Verde and the Cape de Verde Islands ; keeping in longitude between 19° and
20° W. in passing the islands, to avoid some doubtjul dangers placed to the eastward of
* This island was adopted by most of the European nations in the 17th and 18th centuries as the First Meridian, and is still used as such in many of the Swedish, Norwegian, and Russian Maps. Geographers, even of the same country, do not, however, appear to have been unanimous in their assumed Longitude of Ferro, but the English generally reckoned it 17° 40' or 18° W. of London, and the French 20° or '20° 20' W. of Paris! In the Swedish Charts of the late Admiral Klint, it is assumed 20° 30' W. of Paris.
CAPE DE VERDES. 13
them, which seem to have no existence: other ships keep nearer to the continent, where the channel is clear, with soundings near the land. Were it not for great liaze contigu- ous to the coast, occasioned by the dust and dry vapour, driven to seaward by the N.E. winds from the hot sandy desert, the passage within a moderate distance of the main would be preferable to that outside the Cape de Verde Islands, when the sun is far to the southward ; for steady northerly winds then prevail near the continent, and the route fs shorter than that to the westward. But the obscure atmosphere renders the inner passage unpleasant when observations are not regularly obtained, particularly if near the coast ; for a dangerous reef of rocks, part of them above water, projects from cape de Verde Cape de Verde about a league to the westward. Capt. Bathie, in the Evander, ^^"''^• in 1826, was set by the current into the deep bay on the North side of the Cape, and had no soundings with 100 fathoms line, about 3 miles oft" shore ; the Cape bearing W.S.W. about 5 leagues distant; nor were any soundings got afterwards in passing within a few miles of the above-mentioned reef.
THE CAFE DE VERDE ISLANDS, consisting often principal, and some small capedeVerde Isles, extend from lat. 14° 43' to 17° 13' N., and from Ion. 22° 28' to 25° 27' W. ; they i^'""^'- are mostly high, and some of them have sheltered bays, with tolerable anchorage.
ST. ANTONIO, the north-westernmost of the Cape de Verde Islands, is often st. Antonio. seen by ships passing to the westward of them : prior to the use of chronometers and lunar observations, it was desirable to see this island, or Palma, or Madeira, in order to correct the reckoning; which is not requisite, if a ship have good chronometers; nevertheless, St. Antonio may be passed in sight, without fear of delay by calms or light winds, if not approached too close. By admeasurement, I made the summit of St. Antonio 7,400* feet above the surface of the sea, it may therefore be seen near 30 Height. leagues from a ship's deck in clear weather, which is seldom the case, hazy or cloudy weather mostly prevailing about these islands.
Ponta de Sol, the North Point, which may always be known by several white houses on it, projects in a low sand, with a reef extending about ^ a mile farther into the sea, and i^ miles off" the point, the Leven got no ground at 130 fathoms. From hence to the West end of the island, the coast should not be approached within 2 miles, for fear of calms. Between the North and N.E. points, a vessel should not come within 5 miles of the land, as she may have light winds, and be set on the island by the swell. By the survey of H.M.S. Leven, the North Point of the island is in lat. 17° 12' N., Ion. Position. 25° 6' W. ; South Point, in lat. 16° 54' N., Ion. 25° 18' W. ; East Point, 17° 5' N., Ion. 25° 0' W. ; West Point, 17° 3' N., Ion. 25° 23' W.f
On the west side of the island there is a small Bight, called Tarrafal Bay, where larrafai Bay. excellent fresh water may be got, and anchorage in from 35 to 40 fathoms, about ^ mile off" the sandy beach at that part of the bay, where H.M.S. Leven remained some time in the summer of 1820 ; there was very little surf, the anchorage being protected from the N.E. trade wind by the mountainous land ; and this sometimes produced a light sea breeze or eddy wind in the heat of the day.
This bay is known by a small green plantation, and a black sandy beach under a
* Captain Foster made it only a few feet in excess of the above.
t The Russian circumnavigator, Captain, novsr Admiral Krusenstern, made the S. \V. point in Ion. 25° 24' W. Captain Lisiansky made it in Ion. 25° 23' W. ; I made the summit of the island, by noon observation and chro- nometers, in lat. 17° 2' N., Ion. 25° 25' W. Capt. Foster, in H. iM. S. Chanticleer, in 1828, made the beach near the West Point in lat. 17° 1' 4" N., Ion. 25° 15' 5" W.
14 CAPE DE VERDES.
clifl'. The sqtiare sails should be furled, and all the boats made ready to tow a ship in when she is becalmed under the high land, and the jolly boat should be pre- viously sent in and anchored in 30 fathoms as a guide, opposite to a red mark in the cliff. AiTchorage. Tiic best auchorage is in 39 to 35 fathoms, about -^ of a mile offshore, soft bottom,
where a ship may lie very smooth under the mountain, with its altitude about 25° ; northern extreme of the land bearing N. 11° W., southern extreme S. 25° W., red mark on the cliff S. 30° E. This bay is open from N. by W. to S.W. by S. Capt. Vidal made the Tent erected for observations on shore, in lat. 16° 57' 10" N., Ion. 25° 24' 48" W.* Variation 10° VV. (1820.)
* Lieut. Ilaper, R.N., adopts 25° 21' 40" W. as the longitude of Tarrafal Bay, and 25° 2.3' W. for that of the West point. Lieut. Raper has recently devoted his attention to the discussion of the longitudes of the principal maritime points of the globe, and from the judgment and ability which he has displayed in the inquiry, every confidence may be justly given to his decisions which a necessarily imperfect data will warrant.
He has considered separately the absolute position of each place as afforded by astronomical observation, and the relative position as connected by chronometer with other points. The places are arranged in the order in which they are deduced from each other, and the evidence under each is disposed chronologically, by which arrangement the connection between them is clearly exhibited ; so that whenever it may be found necessary to apply a correction of any kind to one or more places, the corresponding effect upon all positions connected with them may be immediately traced.
The entire discussion of this subject will be found in the Nos. of the Nautical Magazine for 1839 and 1840, in a series of papers, which are well worthy the attention of all who are interested in the improvement of hy- drography. We here introduce a few brief remarks from them.
After giving an abstract of the principal voyages and surveys by which hydrography has been chiefly advanced, and considering the comparative value of the various methods employed in determining the longi- tude, Lieut. Raper notices the confusion which arises from navigators acting too independently of each other, in giving new determinations to points fixed by their predecessors. By this unsystematic mode of proceeding, he observes, " Many principal stations, together with the numerous points depending on them, are in per- petual change. Nor is this all, for as navigators do not agree in referring the same places to the same principal station, the determinations of the same place by different navigators cannot be directly compared."
To remedy these evils, he proposes to select certain stations as fundamental points, calling their meridians Secondary Meridians. The longitudes of these points would be assumed as given, and each navigator should be instructed to refer all his positions to them, directly or indirectly, as opportunity offered.
When a point is once agreed upon for a secondary meridian, any other point well determined from it will equally serve for extending the connection to more distant places. " Thus, Capt. Horsburgh having adopted the Grand Ladrone as the principal, or as we should call it, the secondary meridian of the China Sea, connected with it Pulo Aor, about 1,300 miles distant, and 9° 10' 20" W. as given by 20 chronometers agreeing within 2' of each other ; whence Pulo Aor has itself become a position of nearlv equal value with the Grand Ladrone." In this way the islands of the Eastern Sea would by degrees be connected with one another, and agreement would be introduced among their relative positions, which never could result but by accident from chronome- tric measures taken sometimes from places connected with others, and sometimes from places independently fixed.
" The absolute longitudes of these points would be of secondary importance, since consistency among the several places is of far more consequence than their absolute positions. The longitudes would be adjusted in the course of time, but no alterations should be suffered until unequivocal proofs had been accumulated of the necessity of applying corrections."
The number of secondary meridians would of course be indefinite. The following are some of the places submitted by Lieut. Raper as the chief points to which in general all other places in the South Atlantic and Eastern Seas should ultimately be referred, and which are at such distances from each other as to require that they should themselves finally depend on astronomical observation : —
Ptio DE Janeiro, Fort Villegagnan, for the East Coast of S. America.
Cape of Good Hope, Observatory, ,, South Coasts of Africa.
Mauritius, Cooper's I. Port Louis, ,, Indian Ocean.
Bombay, Observatory, „ W. Coast of India, Arabia, and Red Sea.
Madras, Observatory, ,, E. Coast of India and Bay of Bengal.
Batavia, Observatory, ,, Java and adjacent Islands.
Canton, Factories, ,, China Sea and Coasts.
Paramatta, Observatory, ,, Australia.
I
CAPE DE VERDES. 15
The channel between St. Antonio and St. Vincent is safe: the Lord Eldon passed ciiannci ik- throiigh it in July 1802, and thought it nearly 5 leagues broad. In passing through, ["nTo'ami sfi"" you may be guided by your eye to keep clear of the light winds occasioned by either vincom. island.
ST. VINCENT, 7 miles S.E. of St. Antonio, is about 12 miles long from East to West, st. vincm. and 7 broad, having two chains of mountains running parallel to its South and N.E. sides, with a valley in the centre, at the N.W. opening of which is the bay of Porto Grande — the best anchorage in the Cape de Verdes. Here is security from the sea, with a fresh breeze generally blowing, and as much wood may be cut in a short time as can be stowed away, and a