Physiologic Optics is a science which, on the one side, touches the highest philosophic problems of the human mind and, on the other side, keeps in intimate contact with the practical work of the ophthalmologist, who, in his daily work of refraction, can be guided safely only by its principles.<br><br>Many are the text-books on this important subject. Some are mere compilations of older facts and some are written by men that soar so high above the field of the practical work of the ophthalmologist that their abstract scientific investigations lose almost all contact with these practical workers.<br><br>The present book is neither a mere compilation nor an abstract theoretical investigation, but a collection of all the old and new scientific facts that have any bearing on the practical work of the oculist and optician. It is written by a man who lately has probably done more original work in this line than any other since Helmholtz and Donders, and who, furthermore, has been in constant contact with practical ophthalmology. - Dr. M. Tscherning, who was born in Denmark in 1854, studied ophthalmology at Copenhagen under the philosophic mind of Hansen Grut. Since 1884 he has been adjunct-director of the laboratory of ophthalmology at the Sorbonne, where, since the deplorable disability of Javal, he himself has performed the functions of the director. This laboratory, which was founded in 1876 for Javal, after he had become widely known by his translation of the Physiologic Optics of Helmholtz, has given a new impetus to this science in France.<br><br>Here Tscherning has made all his important original investigations, especially on ophthalmometry, the catoptric images of the eye, astigmatism, spherical aberration and accommodation.