LIST OF SUBSCRIBERS.

His Royal Highness the Duke of Clarence and St. Andrews, Lord High Admiral of the United Kingdoms of Great Britain and Ireland, &c. &c. &c.

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The Right Honourable and Honourable the Directors of Greenwich Hospital.
The Committee of Lloyd's, Ten Guineas for 2 copies.

The Royal Naval Club, New Bond Street.

The British Library, St. Helier's, Jersey.

Capt. R. Anderson, R.N.

Capt. F. W. Austen, C.B., R.N., Gosport,

Lieutenant J. W. Aldridge, R.N., North Street, Bristol.

Lieut. H. T. Austin, R.N., Chatham.

Mr. Herbert Allen, H.M.S. Heron.

Henry Adcock, esq., Polygon, Somers' Town.

Vice Admiral the Hon. Sir Henry Blackwood, bart. K.C.B., Commander in

Chief at the Nore.

Commodore C. Bullen, C. B.

Capt. H. W. Bayfield, R.N.

Capt. A. B. Branch, R.N.

Capt. J. W. Beechey, H.M.S. Blossom.

Capt. Edward Brace, C.B., R.N.

Capt. R. L. Baynes, H. M. S. Alacrity.

Lieut. A. B. Becher, R.N., Hydrographical Office, Admiralty.

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The Honourable Frederic Byng.

Lieut. Jacob Bucknor, R.N.

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Mr. Wm. H. Brown, Purser, H.M.S. Musquito.

Mr. W. P. Browne, R.N., Plymouth.

Mr. John Browning, R.N., Ann's Hill Place, Gosport.

Thomas Best, esq.

Alexander P. Bond, esq., Edgeworthstown, Ireland.

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Admiral Sir Isaac Coffin, bart., Titley Court, Hereford.

Vice Admiral Sir Edward Codrington, G.C.B., Commander in Chief, Mediter

ranean, 6 copies.

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Capt. Benj. Clement, R.N., Chawton, Hants.

Capt. Augustus W. J. Clifford, C.B., H.M.S. Undaunted.

Capt. Charles Crole, R.N.

Capt. E. Curzon, H.M.S. Asia.

Lieut. Edward St. L. Cannon, H.M.S. Wolf.

Mr. James Cannon, H.M.S. Thetis:

Lieut. W. J. Cole, Royal George Yacht.

Lieut. P. E. Collins, R.N.

Lieut. Edward Corbet, R.N.

Mr. Champronier, H.M.S. Eden:

Mr. Thos. Cox, Purser, H. M.S. Pyramus.

Simon Cock, esq. New Bank Buildings, London.

William Curtis, esq., Portland Place.

The Rev. Colin Campbell, Widdington Rectory, Bishop's Stortford, Essex.

Mr. Comerford, Bookseller, Portsmouth, 6 copies.

Mr. Crew, Bookseller, High Street, Portsmouth, 6 copies,

Capt. Nevinson De Courcy, R.N., Stoketon House, Plymouth.
Capt. Manley Hall Dixon, R.N., Stoke, near Devonport.

Capt. George Shepherd Dyer, R.N.

Lieut. Henry M. Denham, Linnet Surveying Vessel.

The Rev. E. Davies, H.M.S. Pyramus.

Douthwaite, esq., Commander of the Circassian India Ship.

Admiral the Right Hon. Lord Viscount Exmouth, G.C.B.
Capt. R. Evans, R.N.

Lieut. The Hou. Wm. Edwardes, H.M.S. Asia.

Lieut. John Evans, (a) R.N.

Lieut. Thos. Eyton, R.N.

Lieut. W. W. Eyton, H.M.S. Wolf.

The Rev. J. M. Edwards, H.M.S. Galatea.

THE

DESCRIPTION AND USE

OF THE

TABLES;

WITH THE

PRINCIPLES UPON WHICH THEY HAVE BEEN COMPUTED.

TABLE I.

To convert Longitude, or Degrees, into Time, and conversely.

THIS Table consists of six compartments, each of which is divided into two columns: the left-hand column of each compartment contains the longitude, expressed either in degrees, minutes, or seconds; and the right-hand column the corresponding time, either in hours, minutes, seconds, or thirds. The proper signs, for degrees and time, are placed at the top and bottom of their respective columns in each compartment, with the view of simplifying the use of the Table:-hence it will appear evident that if the longitude be expressed in degrees, the corresponding time will be either in hours or minutes; if it be expressed in minutes, the corresponding time will be either in minutes or seconds; and if it be expressed in seconds, the corresponding time will be expressed either in seconds or thirds. The converse of this takes place in converting time into longitude.

The extreme simplicity of the Table dispenses with the formality of a rule in showing its use, as will obviously appear by attending to the following examples.

Example 1.

Required the time corresponding to 47:47:47" of longitude?

47 degrees, time answering to which in the Table is 3 8" 0: 0:
47 minutes, answering to which is

. 47 seconds, answering to which is

Lon. 47:47'47", the time corresponding to which is

B

.0. 3. 8. 0

0.0. 3. 8

Example 2.

Required the longitude corresponding to the given time 8:52" 28!? 8 hours, longitude answering to which in the Table is 120:0:0: .52 minutes, answering to which is

. 28 seconds, answering to which is

13.0.0
0.0.7

133:0:7"

Besides the use of this Table in the reduction of longitude into time, and the contrary, it will also be found very convenient in problems relating to the Moon, where it becomes necessary to turn the right ascension of that object into time.

Example.

The right ascension of the Moon is 355:44:48"; required the corresponding time?

355 degrees, time answering to which

2340 0:0:

Right ascension 355:44:48%, the time corresponding to

which is

0. 0. 3.12

23:42 59:12:

Since the Earth makes one complete revolution on its axis in the space of 24 hours, it is evident that every part of the equator will describe a great circle of 360 degrees in that time, and, consequently, pass the plane of any given meridian once in every 24 hours; whence it is manifest that any given number of degrees of the equator will bear the same proportion to the great circle of 360 degrees that the corresponding time does to 24 hours; and that any given portion of time will be in the same ratio to 24 hours that its corresponding number of degrees is to 360. Now since 24 hours are correspondent or equal to 360 degrees, 1 hour must, therefore, be equal to 15 degrees; 1 minute of time equal to 15 minutes of a degree; 1 second of time to 15 seconds of a degree, and so on. And as 1 minute of time is thus evidently equal to 15 minutes or one fourth of a degree, it is very clear that 4 minutes of time are exactly equal to 1 degree; wherefore since degrees and time are similarly divided, we have the following general rule for converting longitude into time, and vice versa.

Multiply the given degrees by 4, and the product will be the corresponding time:-observing that seconds multiplied by 4 produce thirds; minutes, so multiplied, produce seconds, and degrees minutes; which, divided by 60, will give hours. The converse of this is evident :-thus,

reduce the hours to minutes; then these minutes, divided by 4, will give degrees; the seconds, so divided, will give minutes, and the thirds, if any, seconds. Hence the principles upon which the Table has been computed. The following examples are given for the purpose of illustrating the above

The depression or dip of the horizon is the angle contained between a horizontal line passing through the eye of an observer, and a line joining his eye and the visible horizon.

This Table contains the measure of that angle, which is a correction expressed in minutes and seconds answering to the height of the observer's eye above the horizon; and which being subtracted from the observed central altitude of a celestial object, when the fore observation is used, or added thereto in the back observation, will show its apparent central altitude. The corrections in this Table were deduced from the following considerations, and agreeably to the principles established in the annexed diagram.