Just published, in one Vol. 8vo. Pr. 6s. bound. HE Second Edition of MATHEMATICAL ESSAYS; being Effays on Vulgar and Decimal Arithmetick, containing not only the practical Rules, but also the Reasons and Demonftrations of them; with fo much of the Theory, and of univerfal Arithmetick, or Algebra, as is neceffary for the better understanding the Practice and Demonftrations: With a general Preface on the Ufefulness of mathematical Learning. Alfo a Collection of arithmetical Questions and Answers from more than 20 Authors and fome Manufcripts. Defigned for the Ufe of Schools. By BENJAMIN DONN. Sold by W. JOHNSTON, in Ludgate-ftreet; B. Law, in AveMary-Lane, &c. N. B. The Collection of Questions may be had feparate, Pr. 18. entitled, The Schoolmaster's Repofitory, or Pupil's Exercise, intended as a Supplement to the Mathematical Effays. In the Mathematical Essays, p. 323, for right r. left; and for left r. right: Alfo for 763 2417 r. 7629.4317. Τ' Just published in one Vol. 8vo. Pr. 35. 6d. bound. HE Second Edition, with Additions and Alterations, of By JOHN ROWE. Sold by J. JOHNSON, oppofite the Monument. In January 1765 will be published, in one Vol. 8vo. Price to Subs A scribers 45, fewed, Treatife of Gauging, by THOMAS MOSS. Containing not only what is common on the Subject, but likewise many curious and useful Improvements. Sold by Mr. Owen, near Temple-Bar; Mr. Stuart, in Paternofter-Row; Mr. Johnson, oppofite the Monument; and the Author, in Roe-buck-Court, Chifwell Street. Alfo on 12 Sheets of Imperial Paper, Pr. 11. 11s. 6d. MAP of the County of DEVON, delineated from an actual A DONN, engraved THOMAS JEFFERYS, Geographer to His Majesty. Sold by the Print-Sellers of London, the Author, and the Bookfellers of Devon. Plane Trigonometry. With their APPLICATION to ALTIMETRY and LONGIMETRY. BY BENJAMIN DON N. Trigonometria plana eft fcientia ex tribus trianguli rectilinei partibus inveniendi reliquas. The PRE FACE. H AVING already given the Elements of Geometry, we come now to treat of Plane Trigonometry. It is by Trigonometry that we apply Geometry to find the Heights of Objects and Distances of Places, both on Sea and Land, as is fhewn in this Effay. Hence it appears, that, even in the narrow Limits to which it is here confined, it is a Science of great Ufe in the common Affairs of Life; and, if we include the Doctrine of spherical Triangles alfo, under the Term Trigonometry, it is that Science to which may be attributed whatever is effected in Aftronomy, Geography, and Navigation, agreeably to the Motto prefixed to this Volume. For by Trigonometry it is the Aftronomer computes the Distances of the Planets, calculates the Eclipfes of the Sun and Moon, the Tranfits of Venus and Mercury, conftructs Dials for fhewing the true Time of the Day, &c. By it the Geographer lays down the principal Places on the terraqueous Globe in their true Pofitions and Distances: And, laftly, by it the Navigator conducts his Ship, through the tracklefs Ocean, to his defired Port, though ever fo far diftant, by the uncertain Impulse of the Wind. ་ What we have attempted to do, in this Effay, is, to give the Elements of Plane Trigonometry in a clear Manner, with their Application to Altimetry and Longimetry, in a greater Variety of ufeful Problems, both for Land and Maritime Surveying, than is given in any other Treatife on this Subject. A 2 And |