822 J. LeConte on Binocular Vision. 
seen by both eyes. Now place a second screen C across the 
visual line A R of the right eye, so as to intercept rays from 
6. the object A to the right eye. Neverthe- 
’ less, the object A will be seen apparently 
through the opaque screen C, which will 
therefore appear transparent, and may even 
be drawn in outline with accuracy on the 
screen at b exactly where the visual line of the 
right eye pierces the screen—exactly where, if 
the screen were transparent ground glass, we 
would see it with the right eye, and might 
trace its outline. M. Pictet thinks this ab- 
solutely explicable, except on the assump- 
tion that an illusive image is actually seen 
at A by the right eye; and that it is this 
that we draw in outline on the screen at 4, 
the screen being transparent because the il- 
lusive image is seen beyond. 
But M. Pictet gives another experiment 
which he thinks still more conclusive. 
a sheet of paper lying on the table place 4 
piece of money; then place a screen upright on the right side 
2 oO 
piece of money, we see that the 
vertical screen appears transparent 
throughout, and that 77 perms the 
right eye to distinguish the prece, as 
if through a very diaphanous sur 
face.” “Tf now we give to 
optic axes a direction more paral- 
lel, we see the image of illusion ol 
he right eye move gradually 
ward the right, traverse the line of 
intersection of the screen and thé 
table, and come to project itself OB 
the other side upon the pape! 
where we may trace its outline 
correctly.” To brent these facts more clearly I give the 
n 
directing the regard upon “ 
a 
et 
? = 
look at the piece of money. 
through the screen, Rd the visual line ol 
3 ye 
A and seem to see it 
