REVIEWS. 
267 
SIGHT.* 
T HE function of sight has engaged so much study, that one marvels that 
no one should till now have undertaken to explain its chief phenomena 
to the reading public. The physiological aspects of the eye have been fully 
discussed in Michael Foster’s Physiology, for instance, and the physical con- 
siderations are sufficiently explained in most treatises on Optics ; but Prof. 
Le Conte, in a volume of the International Scientific series, presents us with 
a larger view of this subject than comes under the consideration of a special- 
ist. The author is a master of the art of professional exposition, singularly 
clear, full of information, and often original in his own views as well as in 
stating those of others ; and, therefore, his work fills a gap in literature 
in an able way. The volume is divided into three parts, which concern 
monocular vision, binocular vision, and disputed points in. binocular vision. 
After a short introduction, which explains the relations of the senses to the 
phenomena with which they are concerned, the first part gives an admirable 
account of the elementary physiology of the eye, in four chapters which 
concern its general structure, the formation by it of images, its properties 
as an optical instrument when compared with the work of the optician, some 
of its defects, such as old-sightedness and near and long sight, and the struc- 
ture and functions of the retina. The second part of the work contains 
much that is novel, for few persons consider the relation of their eyes to 
each other. It is shown that everyone sees double, and that most persons 
are right-eyed, just as they are right-handed, because they are, as the author 
phrases it, left-brained. And an explanation is given of the reason why 
objects beyond or nearer than the point of sight are always seen double. 
The superposition of images, binocular perspective, and judgment of dis- 
tance, size, and form, are the other subjects of this part. The perception of 
double images is a distinctive view, and leads the author to certain differ- 
ences from the theories of Wheatstone and Briicke. The third part deals first 
with the laws of the motions of the eyes, which are considered to be parallel 
or convergent motions. A chapter is devoted to the horopter. It is obvious, 
that as each eye forms its image, and as the images are brought together and 
superimposed at the point of sight, the sum of the points which appear 
single, while the point of sight is unaltered, or horopter, may be a line or a 
plane. The author considers it to be a line. This and many other original 
views, well set forth, will ensure careful consideration for the physiological 
studies of one who has already enriched geological science with many new 
facts and important theoretical views. 
* Sight : an Exposition of the Principles of Monocular and Binocular 
Vision. By Joseph Le Conte, LL.D., Prof, of Geology and Natural History 
in the University of California. With Numerous Illustrations. 8vo. 
London: C. Kegan Paul & Co. 1881. 
