Elements of Plane Trigonometry Some apology is required for ading another to the long list of boks on Trigonometry. My excuse is that during twenty years' experi- ence I have not found any published bok exactly suiting the wants of my Students. In conducting a Junior Clas by regular progresive steps from Euclid and Elementary Algebra to Trigonometry, I have had to l up by oral instruction the gap betwen the Sixth Bok of Euclid and the circular measurement of Angles, which is not satisfactorily bridged by the propositions of Euclid's Tenth and Twelfth Boks usualy suposed to be learned, nor yet by demonstrations in the modern boks on Trigonometry, which mostly folow Wodhouse, while the Apen- dices to Profesor Robert Simson's Euclid in the editions of Profesors Playfair and Walace of Edinburgh, and of Profesor James Thomson of Glasgow, semed to me defective for modern requirements, as not suciently conected with Analytical Trigonometry. What I felt the want of was a short Treatise, to be used as a Text Bok after the Sixth Bok of Euclid had ben learned and some knowl- edge of Algebra acquired, which should contain satisfactory demon- strations of the propositions to be used in teaching Junior Students the Solution of Triangles, and should at the same time lay a solid founda- tion for the study of Analytical Trigonometry.