ELEMENTS OF PLANE TRIGONOMETRY. BY JAMES HANN, FORMERLY MATHEMATICAL MASTER, KING'S COLLEGE SCHOOL, VIRTUE BROTHERS & CO., 26, IVY LANE, PATERNOSTER ROW. 1867. 183.9 21. PREFACE TO THE THIRD EDITION. IN submitting this Rudimentary Treatise on Plane Trigonometry, after its having been carefully revised and corrected, the author would also respectfully invite the reader's attention to the collection of Mathematical Tables, forming part of this Series of Scientific Treatises; they will be found amply sufficient for all the practical purposes of Trigonometry, and will therefore furnish all the aid necessary in computations connected with the present subject. The author has given, to illustrate the principles, a great number of examples fully worked out, and which will be of service to those who have not the aid of a teacher. "In compiling the work, the best authors, whether French or English, have been consulted. Amongst others, those of Bonnycastle, Cape, De Morgan, Gaskin, Hall, Hind, Hymers, Snowball, Woodhouse, and Gregory; with Davies's edition of Hutton's Course. “The problems have been principally taken from the Ladies and Gentleman's Diaries, the Cambridge Problems, and Laybourn's Repository. "The demonstration of Demoivre's Theorem is taken from an able French work on Trigonometry, by Lefebure De Fourcy." J. HANN. A° α r arc ; radius which is called the circular measure of the angle. From equation (2) we see that the measuring unit, U, а must be multiplied by the fraction to find the angle; γ Now, suppose we take an angle of 22° 27′ 39′′, then this is put into decimals at once by the centesimal division, without putting down any work on paper, it being 220-2739; whereas, by the sexagesimal, we must proceed in the following manner: 60) 39 60/ 27.65 22.4608 If we wish to find how many grades and minutes are contained in this angle, here |