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BY JEREMIAH DAY, D. D. LL.D.
President of Yale College.

THE SECOND EDITION,

WITH ADDITIONS AND ALTERATIONS.

NEW-HAVEN:

PUBLISHED BY HOWE & SPALDING.

S. CONVERSE, Printer.

BY JEREMIAH DAY, D. D. LL.D.
President of Yale College.

THE SECOND EDITION,

WITH ADDITIONS AND ALTERATIONS.

NEW-HAVEN:

PUBLISHED BY HOWE & SPALDING.

www

S. CONVERSE, Printer.

DISTRICT OF CONNECTICUT, s.

BE IT REMEMBERED, That on the twenty-ninth day of July, in the forty-ninth year of the Independence of the United States of America, JEREMIAH DAY, of the said District, hath deposited in this Ofice the title of a Book, the right whereof he claims as Author, in the words following

"A treatise of Plane Trigonometry; to which is prefixed a summary "view of the nature and use of Logarithms: being the second part of a "course of Mathematics, adapted to the method of instruction in the Ameri"can Colleges. By Jeremiah Day, D. D. LL. D., President of Yale College. The second edition, with additions and alterations."

In conformity to the Act of the Congress of the United States, entitled "An Act for the encouragement of learning, by securing the copies of Maps, Charts, and Books, to the Authors and Proprietors of such copies, during the times therein mentioned."

CHAS. A. INGERSOLL, Clerk of the District of Connecticut.

A true copy of Record, examined and sealed by me,

CHAS. A. INGERSOLL, Clerk of the District of Connecticut.

THE
HE plan upon which this work was originally commen-
* ๆ
ced, is continued in this second part of the course. As
the single object is to provide for a class in college, such
matter as is not embraced by this design is excluded. The
mode of treating the subjects, for the reasons mentioned in
the preface to Algebra, is, in a considerable degree, diffuse.
It was thought better to err on this extreme, than on the
other, especially in the early part of the course.

The section on right angled triangles will probably be con-
sidered as needlessly minute. The solutions might, in all
cases, be effected by the theorems which are given for ob-
lique angled triangles. But the applications of rectangular
trigonometry are so numerous, in navigation, surveying, as-
tronomy, &c. that it was deemed important, to render famil-
iar the various methods of stating the relations of the sides
and angles; and especially to bring distinctly into view the
principle on which most trigonometrical calculations are
founded, the proportion between the parts of the given tri-
angle, and a similar one formed from the sines, tangents, &c.
in the tables.