The New Practical Navigator

deavoured to render this part of the Nautical Art as fimple and plain as the nature of the fubject will admit.

To the Defcription of HADLEY'S QUADRANT is added the Defcription and Ufe of HADLEY'S SEXTANT, with an Account of the new Mode of dividing the Nonius, fo that the Distance can be read off to fifteen feconds. The Method of adjufting the Sextant and Telescope is fully enlarged upon, together with the use of this Inftrument, in obferving the angular distance.

PARALLAX and REFRACTION are next defined, and illuftrated with a Plate. The Method of applying the Corrections for Parallax and Refraction to the observed Distance, in order to reduce it to the true, is next given.

It being frequently complained to me by feamen, that it is next to impoffible to find and know the Stars from which the Moon's distance is computed in the Nautical Almanack, I have, to remedy this defect, fubjoined to this Work two plans of the Stars, one on the Plane of the Equator, the other on the Plane of the Meridian; a defcription of the projection and ufe of these Plans is given at large in the Work, together with fome PRACTICAL DIRECTIONS for knowing the Stars.

Next in order is the Method of finding the TRUE TIME, in order to regulate the going of the Watch. The Lunar Obfervations follow, arranged in a new, clear, and perfpicuous manner. The Examination of a YOUNG SEA OFFICER, being an Abftract of practical Seamanship, has been examined by two profeffional men, and large additions made.

We have also added, what we conceive will be an acceptable article in the prefent times of hoftility,-The Method of exercising private Ships' Companies for War. In this article, the forms of two Quarter Bills are given, with the Exercife of the great Guns, according to the prefent practice, and fome approved manœuvres in attacking and defending a fingle fhip. Two additional Tables will alfo be found, one exhibiting the Proportion of Powder for Sea-Guns, the other the Number of Shot contained in Grapes of different Sizes.

A variety of Methods of relieving Ships in Diftrefs; the beft Means of faving people from Wrecks; and the Procefs recommended by the Royal Humane Society for recovering drowned Perfons, will also be found.

To the Tables a folicitous attention has been paid. The Tables of Difference of Latitude and Departure for Points and Degrees, have been re-calculated with the greatest care. The Tables of Logarithms of Numbers, and of Artificial Sines, Tangents, and Secants, have been carefully compared with the third edition of Hodgfon's Tables, printed in the year 1738; with Gardner's third edition of Sherwin's, printed in the year 1742; and with Dr. Hutton's laft edition, by three per. fons; fo that I trust the errors, if any, are few.

The Tables which follow have undergone a fimilar examination. To the Tables of the Sun's Declination, a moft fcrupulous attention has been paid. The Table of Latitudes and Longitudes of Places is corrected by the lateft furveys and obfervations, and great additions made.

Table XIII. For reducing the Sun's Declination to any given Meridian, and to any time under that Meridian, in the first page of

which

which you have the Proportional Parts of the Daily Difference of the Sun's Declination to every Minute and every fix Seconds, anfwering to every five Minutes of Time, and to every Degree and fifteen Miles of Longitude. The fecond and third page contain the fame propor tional Parts to every hour, and to every fifteen Degrees of Longitude. To the Table XVI. For turning Degrees and Minutes into Time, and the contrary, two columns are added on the right fide, for turning Minutes and Seconds (of an hour) into Longitude, and the reverse.

Table XVIII. contains the Decimal of every Minute in twelve Hours, being of ready ufe for finding the Proportion of the fmall Dif ference (in twelve Hours) of the Moon's Parallax and Semi-diameter, by taking out the number from the Table anfwering to the Time when the obfervation was taken, and multiply the differences therewith from the product of each, cut off four figures from the right hand, the left hand figures are the Anfwers (if no Fraction remains) which must be additive or fubtractive, according as they are increafing or decreasing. The proportional Part of the Daily Difference of the Sun or Star's right Afcenfion is found by taking out the number, answering to half the time required, and multiply the difference therewith, from the product, cut off four figures from the right hand, the remaining figures are the answer. Thus you avoid working by the the Rule of Three. In the precepts for finding the Longitude by Lunar Obfervation, page 238, you are told to make ufe of the Log Sine of 30 degrees*, half the fum of the apparent Altitudes, and half the apparent Distance.

This Edition has been carefully examined, improved, and corrected by my friend Captain JOSEPH DESSIOU, whofe abilities as a Navigator, Mathematician, and Draughtfman, cannot be doubted. Therefore I may prefume to fay this is the moft correct Edition that has been prefented to the Public's notice.

* The Log Sine of 50 degrees is equal to the Natural Sine of half the Radins; and, according to Euclid, Axiom 6, Book I. what things are each of them half of the same quanity, are equal among themselves.

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