J. LeConte on Binocular Vision. 419 
together by the law of corresponding points. In M. Pictet’s 
experiment these two, the pencil and the money, are similarly 
related to the two eyes, one on one side and the other on the 
other side of the screen—one exposed to the view of one eye 
and the other to the view of the other eye. If the image we draw 
is an illusive image seen by the right eye, then the pencil with 
which we draw must be also an illusive image seen by the left eye. 
But to explain M. Pictet’s experimenta little farther: When 
we look directly at the money, M. Pictet says ‘‘ we see that the ver- 
tical screen is transparent throughout, and that it permits the 
night eye to see the piece as through a perfectly diaphanous 
surface.” But there are two transparent screens seen. e one 
seen by the right eye M. Pictet observes,* the other apparently 
escapes his observation. The truthis, when we look at the money, 
the heteronymously doubled images of the median screen m m’ 
(fig. 14) meet at the distance of the point of sight. The actual rela- 
tion of parts is seen in fig. 7 (p. 322), in which A Rand A Larethe 
visual lines converged upon the piece A. The visual result is 
seen in fig. 14. It is seen that the visual line of the right eye 
Stops at the right eye image of the median screen, while the left 
visual line runs parallel to its image 
of the median screen unobstructed 
to the piece a’. Again, “if we give 
to the optic axes a direction more 
parallel,” says M. Pictet, ‘“‘ we. see 
the image of illusion move gradually 
come on the right side.” “But again, 
he does not observe that there are 
two screens seen; and again, it is 
the left eye image of the screen 
which he neglects. In truth, as the 
eyes become parallel, the two images 
of the screen, mS and m’S’ fig. 14, 
screen seen by the left eye; only the right eye shifts tts image of the 
screen to the left of it. If M. Pictet would place another piece 
- There seems to be a kind of dexterity in the right eye. In many cases of 
double images, most persons habitually neglect the left-eye image. 
