SIGHT: AN EXPOSITION OF THE PRINCIPLES OF MONOCULAR AND BINOCULAR VISION. 66 BY JOSEPH LE CONTE, LL.D. AUTHOR OF ELEMENTS OF GEOLOGY,' "RELIGION AND SCIENCE," AND PROFESSOR OF GEOLOGY AND NATURAL HISTORY IN THE UNIVERSITY OF CALIFORNIA. WITH NUMEROUS ILLUSTRATIONS. THIRD EDITION. LONDON: KEGAN PAUL, TRENCH, TRÜBNER & CO. LTD. 1895. 703883 PREF A СЕ. In writing this treatise I have tried to make a book that would be intelligible and interesting to the thoughtful general reader, and at the same time profitable to even the most advanced specialist in this department. I find justification for the attempt in the fact that there is not, to my knowledge, any work covering the same ground in the English language. Vision has been treated either as a branch of optics or else as a branch of physiology of the nervous system. Helmholtz's great work on "Physiological Optics," of which there exist both a German and a French edition, is doubtless accessible to scientists, but this work is so technical that it is practically closed to all but the specialist. I believe, therefore, that the work which I now offer meets a real want, and fills a real gap in scientific literature. The form in which the subject is here presented has been developed entirely independently, and as the result of a conscientious endeavor to make it clear to students under my instruction. As evidence of this, I would draw attention to the fact that, out of one hundred and thirty illustrations, only about twelve have |