424 J. LeConte on Binocular Vision. 
the operator. A Leyden jar was introduced into the circuit 
in order to increase the brilliancy of the sparks. The sparks 
were 1-2 inches in length. I selected stereoscopic pictures in 
which all other forms of perspective were entirely wanting, so 
that no relief was visible with one eye. Outline geometrical 
gures are best for this purpose. 
I first viewed these in the stereoscope by the continuous light 
When I first commenced my experiments by either of these 
methods, but especially the last, a rapid succession of spar! 
was n inati t 
difficulty in the interval of darkness, After some practice 
however, the rapid succession of sparks was no longer necessary. 
The combination was effected, ana the relief perceived by sepa- 
by monocular vision, even in the full light of day. By the 
x their relative distance was at once detectable with two eyes, 
though not with one. This last experiment was varied in many 
ways, but always with the same result, : 
Stereoscopic combination, by squinting requires considerable 
practice, even in the full light of day, and of course much 
more. by the electric spark. All the other experiments were 
repeated by my brother, and my results confirmed. 
ae ; * II, vol. ii, p. 1. 
