4992 J. LeConte on Binocular Vision. 
this point. The full-lined figs. A and B are two projections of a 
truncated pyramid, as seen by the left and right eye respectively. 
On the same smal- 
gure. These four 
figures, according to 
Pictet, represent 
images formed in 
looking at a a 
truncated pyrami 
the full-lined figures being the true and the dotted-lined figures 
the illusive images. For, says he, “if we unite in oné single 
image these four contours (by means of a stereoscope), we eX- 
perience instantly the impression of. a solid body ; and we 
mon faces, the smal] triangles, are united, the full-lines of the 
ee figure must coincide with the dotted lines of the other. M. 
; mage has therefore, by his dotted lines, only represented in 
oe of his fig ures what must take place in the binocular com- 
mation of his two full-lined Jigures, if there were no dotted lines 
and which forms the foundation of Briicke’s theory. 
b ame rt Prevost and Brewster explain the perception of relief 
ies changes of Optic convergence, by means of which 
ak parts of the two dissimilar images of the same object, 
Wo stereoscopic pictures, are successively united. In 
angles are perfectly united, then th 
7 e smaller triangles are 
doubled. Thus, the alternately greater and less convergence, 
+L. ty, 10 unite successively different parts of the pictures— 
f the point of sight back and forth—precisely 
