The Elementary Theory Of The Symmetrical Optical Instrument is a book written by John Gaston Leathem and originally published in 1908. The book is a comprehensive guide to the principles and mechanics of symmetrical optical instruments, such as telescopes and microscopes. It covers topics such as the theory of lenses, image formation, aberrations, and the design and construction of symmetrical optical instruments. The book is written in a clear and concise style, making it accessible to both students and professionals in the field of optics. It is considered a classic work in the field and is still used as a reference today.This scarce antiquarian book is a facsimile reprint of the old original and may contain some imperfections such as library marks and notations. Because we believe this work is culturally important, we have made it available as part of our commitment for protecting, preserving, and promoting the world's literature in affordable, high quality, modern editions, that are true to their original work.