492 
Le Conte’s book on ‘Sight’ is extremely wel- 
come. It remains true now, as it was in 1880, 
when the first edition was published, that there 
is no other book in the English language cover- 
ing this field. During the past year two excel- 
lent American contributions have, indeed, been 
made to the subject—Professor Bowditch’s sur- 
vey inthe ‘ American Text-book of Physiology’ 
and the various articles in the ‘Systems of Dis- 
eases of the Eye,’ by Norris and Oliver. But 
Professor Le Conte’s book is the only treatise 
covering the subject of vision in English, and, 
in fact, in any language, with the exception of 
the more technical works of von Helmholtz 
and Aubert. While it is surprising, and not 
altogether creditable to the ‘new psychology,’ 
that we have only one book on the subject, it 
is fortunate that it is so excellent. 
Professor Le Conte devotes two-thirds of his 
book to binocular vision. This is excessive for 
a text-book, but it is justified by the interest of 
the subject and by the important original contri- 
butions of the author. Following an introduc- 
tion on the senses, the part on monocular vision 
includes sections on the general structure of the 
eye, the formation of the image, the perfect 
eye, defects of the eye, structure of the retina, 
space perception and color perception. In this 
part should, perhaps, be included the final chap- 
ter on the evolution of the eye, added in this 
edition, which, however, appears as the 7th 
chapter of the third part, entitled in the table 
of contents, ‘Some abstruser points, especially 
in binocular vision,’ and in the text, ‘On some 
disputed points in binocular vision.’ 
The author has added some new matter to 
this first part, especially on color blindness and 
color perception, including a full statement of 
the Donders-Franklin theory. Iregret the omis- 
sion or brief treatment of subjects so important 
as the intensity of sensations, their time rela- 
tions, the field of vision, illusions, the combina- 
nation of colors,* etc. It isin any case evident 
that everything cannot be included in 100 
pages, and it is a wonder that Professor Le 
Conte has been able to give with such clearness 
somuch. There are several points on which I 
*Fortunately some of these topics are fully treated 
in another admirable book in this same series, Pro- 
fessor Rood’s ‘ Modern Chromatics.’ 
SCIENCE. 
[N.S. Voz. VI. No. 143. 
should differ with the author. For example, 
the explanation of ‘upright vision,’ which has 
been discussed in this JouRNAL. Professor 
Stratton, a colleague of Professor Le Conte’s at 
the University of California, has since made the 
ingenious experiment of wearing, for several 
days, glasses that inverted the normal retinal 
image and shows how quickly adjustment is 
made. But it is still easier to stand on one’s 
head and notice that the landscape is not seen 
inverted. 
The two parts on binocular vision contain 
clear and concise accounts of experiments 
largely devised by Professor Le Conte. Mak- 
ing these experiments would, as the author says, 
be for any one an admirable culture in scientific 
method. Many of the experiments are valuable 
contributions to science, but the details are 
somewhat complex and cannot be made clear in 
a review. The reader must turn to Professor 
Le Conte’s book, with its many new and in- 
genious illustrations, in order to appreciate the 
importance of a study of binocular vision and 
the great value of the author’s contributions to 
the subject. I may note that I have recently 
been told by an eminent oculist that the con- 
flicting results in the case of Listing’s law 
found by von Helmholtz were due to unrecog- 
nized astigmatism in his eyes. 
There are some points where Professor Le 
Conte’s statements do not seem to me quite ac- 
curate. For example, he says, ‘‘ We always see 
things double, except under certain conditions.”’ 
This is scarcely correct psychology ; we must 
learn by practice to see things double, and then 
usually see them double only while the experi- 
ment lasts. Professor Le Conte says, ‘‘I be- 
lieve that the existence of the central spot is 
necessary to fixed, thoughtful attention, and this, 
again, in its turn, is necessary for the develop- 
ment of the higher faculties of the mind.’’ But 
may not the mental faculties of those born blind 
be developed? There are further many sub- 
jects, such as the horopter, that I cannot regard 
as finally solved by Professor Le Conte, but his 
researches have accomplished much toward 
their solution and should be accepted as the 
basis of future work. 
J. McKEEN CATTELL. 
CoLUMBIA UNIVERSITY. 
