A Treatise on Plane and Spherical Trigonometry

The classic treatise on spherical trigonometry, covering spherical triangles, Napier's rules of circular parts, the solution of oblique triangles and applications to astronomy and geodesy. A clean digital edition with numerous examples.

Isaac Todhunter

A classic college textbook that covers plane trigonometry and then spherical triangles, with applications to geodesy, astronomy and navigation. Includes four-place logarithm tables and many worked problems.

William Anthony Granville

Short, clear notes that derive the fundamental formulas of spherical triangles from plane trigonometry, including the spherical laws of sines and cosines. A quick modern entry point before the classics.

Rob Johnson