226 W. LeConte Stevens—New form of Reversible Stereoscope. 
Art, XXI.—A New Form of Reversible Stereoscope ; by 
W. LeConTe STEVENS. 
Wir a view to removing for others the difficulty implied 
in the binocular experiments on which I based the conclusions 
without special discomfort. It has been constructed for me by 
Messrs. EK. & H. T 
The semi-lenses (fig. 1, /, 2), rest in a pair of boxes, with 
h 
of the screws. 
To secure natural perspective through the semi-lenses, press 
the brass and wooden screens flat (fig. 1) and use the instru- 
eyes to be not greater than usual, comfortable vision will be 
secured by turning the adjusting screws until the semi-lenses 
are pressed as near as possible together. The light which 
enters the pupils then passes through the thicker part of each 
