. 
644 The American Naturalist. [July, 
shortly after midnight. He talks with few persons, shuns large gather- 
ings, reads little, and is but little interested in what he reads, because, 
to use his own expression, ‘ his memory is always in his calculations.’ ” 
In short, while his memory for numbers is abnormally developed, all 
other sides of his intellect are atrophied. The tests which Sign. Guic- 
ciardi and Ferrari undertook along other lines than that of figuring 
failed signally, because of his lack of interest and attention. He was 
always inquiring what was the use of doing these—they were not in his 
line at all. For this reason many of the usual tests had to be aban- 
doned or altered so as to bring in merely numerical data. However, 
these negative results are as truly indicative of his real nature and dis- 
disposition as the successful tests, which they serve to conform. 
Visual Perception of Depth.—Some experiments on the visual 
perception of depth are reported by M. B. Bourdon in the “ Revue 
Philosophique” for January, which, if they warrant the deductions 
which he draws from them, will necessitate a modification of the ac- 
cepted theories of space perception. The special object of the experi- 
ments was to isolate the depth data furnished directly by monocular 
and binocular vision, respectively, from the elements of judgment ordi- 
narily attaching to them—such as known size, brightness, number of 
intervening objects, etc. To accomplish this the tests were made in a 
long hallway in the cellar of a large building and at night, when the 
cellar was completely dark. Two lanterns were placed at different 
distances, their light being of so small an intensity that the hall itself 
was not illumined ; the effect was merely of two bright points of light. 
In the monocular tests, the lights were first placed in position, and 
the subject was then led with eyes blindfolded to the spot chosen; 
one eye remained covered during the experiment. The subject was 
asked to determine which of the lights was the nearer. The experi- 
ment was tried with five subjects, and for distances ranging from 1 to 
30 meters. It was found that even with the latter difference there was 
no preponderance of right judgments, while a slight difference of in- 
tensity between the lights led uniformly to a judgment in favor of the 
brighter. The author concludes that the muscular sensations accom- 
panying changes of accommodation play no part in the estimate of 
depth, at least for distances greater than one meter. 
For the binocular tests the author used two hallways at right angles 
to one another, the subject being stationed at their point of intersection. 
One of the lights was placed in each of the halls. When the further 
light was 25 meters distant, right answers were generally given when 
