J. LeConte on Binocular Vision. 323 
the right eye when the optic axes become parallel, and 4, exactly 
where the visual line of the right eye pierces the paper, the place 
where the outline of the piece may be traced. The image 
moves to the right or left according to the position of the optic 
axes, being always where the visual line pierces the paper 
But “the most eee eous position of the optic axes,” says 
_M. Pictet, “is parallelism, for it is that which removes the farthest 
the image of illusion from the real image.” I wonder that M. 
Pictet did not reflect that, being on corresponding points, by 
his own principle the image of illusion, if any, cannot be separated 
from the real image ; and that there is in fact but one image seen. 
__ But furthermore, if a convex lens be placed across the visual 
line of the right eye Rd, the image at 6 will not be affected, but 
the tracing we make of the image will be found as much smaller 
than the money as the lens magnifies ; showing that the nap 
is not magnified but the drawing is magnified, and therefore, M. 
Pictet thinks, that the image of the money is ilusive or subjective, 
while the image of the paper and of the tracing is real. If, how- 
ever, the lens be placed before the left eye, the mage 1s magnt- 
fied because, thinks M. Pictet, this image is the dlusive raght- 
eye fac-simile of the magnified real image of the left eye. 
One more step of M. Pictet’s proof. By keeping both eyes 
Open, objects in the microscopic field may actually be drawn 
with accuracy on a sheet of paper placed on one side of the 
microscopic tube. Or, still better, if a stereoscopic card, having 
a picture on one half and the other half blank, be placed in the 
Teoscope, we may trace the picture on the bl half <Ac- 
cording to M. Pictet’s view, the light impresses one eye, and 
this impression is propagated as an illusive image to the other 
eye, and thrown on the paper just where the visual line pierces it 
[To be concluded] 
Q1a 
