APPENDIX,

то

Philofophical ESSAYS,

In THREE PARTS:

CONTAINING

A Brief THEORY of the NORTH

Magnetic-Pole,

And of the MARINER's

Compass - Needle;

In order to deduce and afcertain the

LONGITUDE,

From natural and permanent PRINCIPLES.

By R. LOVETT.

Of the Cathedral Church of Worcester.

WORCESTER: Printed by R. LEWIS, for the AUTHOR; by whom they are Sold:

Sold

alfo by Mr. SANDBY in Fleet-Street; J. JOHNSON, and Co. BooKSELLERS, in Pater-nofter Row, LONDON; and by Mr. FLETCHER, BOOKSELLER, in OXFORD. &i. &c.

A Brief THEORY of the

North Magnetic-Pole;

And of the

Mariner's Compafs-Needle.

T may perhaps be thought fomewhat abfurd, or at least out of time, to publish now an Effay for the finding of the Longitude at Sea, after the truly ingenious Mr. Harrifon hath already discover'd it, and to fuch a degree of accuracy and exactnefs, that, on the ftricteft fcrutiny of the moft fevere Examiners, he hath been allowed and adjudged to be juftly entitled to, and hath actually received the parliamentary Premium appropriated to the Perfon who should render fo fignal a Service to the World in general.

2. Far be it from me to envy the worthy Poffeffor the well-deferved Reward of his indefatigable Labours; his Perfeverance for upwards of forty Years in the arduous purfuit of fo important an object cannot be enough commended:

mended; and I heartily join his numerous Wellwifhers in congratulating him on his Succefs. He must be allowed by all competent judges to have excelled every other Artift in compleating a Time-keeper, which, on repeated trials, hath answered the great purposes expected from it; and may it ever continue to do fo! But who can engage that any Machine, though conftructed on the niceft Rules of Art, fhall never be out of order? And granting it moves invariably right, will its warmest abettors venture to affert that it has effected the Discovery of every Thing ufeful to the Mariner, fo as to fuperfede all farther Enquiries, and to render them unneceffary? Has it, for inftance, pointed out that great defideratum the Caufe of the Variation of the Needle? Has it fixed, or fhewn us where the firft or grand Meridian is, or ought to be fixed; or indeed whether it is fixed at all? And if not, does it fhew us how it is to be found, in order that the fame Calculation of Longitude might ferve all Nations? Many more Questions might be afked; but thefe are abundantly fufficient to convince us that farther Difquifitions on the Longitude cannot be juftly deemed either useless, or unfeafonable; for, as our methods of proceeding are on quite different Principles, it is impoffible that what I have to offer in the following Pages fhould be anticipated or rendered unneceflary by Mr. Harrison's Machine, even allowing it to be perfect.

But fince there are probably many, who do not well know what the Longitude means, it may be useful to fubjoin a brief explication of it; (See Pl. IV. Fig. ft. of the Appendix) where E, N, W, S, reprefent the Horizon; C, the Center; E, A, W, the Equator; P, the north Pole of the Equator: The feveral curve lines on each fide of the Equator are called parallels of Latitude: The reft of the curve lines which interfect the feveral Parallels of Latitude, and all of them at the Poles, are Meridians of Longitude, at 15 Degrees diftance from each other, equal to an Hour in Time; and this leads me to point out how the Longitude may be difcover'd by Time-keepers, fuch as accurate Clocks, Watches, &c.

4. As every Circle, great or fmall, contains 360 Degrees, and as the Sun in appearance compleats a Circle round us in 24 hours; fay ho. deg. ho. deg. by the Rule of Proportion, If in 24: 360: 1:15 Then to find how much difference of Time is equal to a fingle Degree of Longitude, it will be, if 15° be equal to 60' of Time, 1° will be equal to 4 Minutes of time; confequently every single minute of time is proportionable to a quarter of a Degree of a Circle; i. e. one fourth of a Degree of Longitude.

5. And as the Sun is in fome Meridian or other to the Eaft of London all the forenoon, and therefore before London in Time; confequently it is to the West in the afternoon, and therefore after London.