MICROSCOPY. 499 
the objective. With the highest objectives generally used with 
black ground illumination, as a jth of 75° to 110°, the object seems 
no brighter than usual, but the field is free from the foggy diffuse 
light, otherwise present, and the object appears, beautifully dis- 
tinct, upon a jet black ground. Even a ith or 4th of 130° gives 
the same effect of a deep black background, and shows the object 
with good stereoscopic effect in Wenham’s binocular. With ob- 
jectives of 170°, the main effect is that of a dark background, 
though not so perfect as with the lower angles.—T. D. B 
Bicuromatic Viston.— Mr. J. W. Stephenson, inventor of the 
recent binocular microscope which bears his name, has noticed 
that if different colors are presented, simultaneously, to the two 
eyes, the sensation produced will be that of neither of the two 
together. If the colors presented are strictly complementary, the 
effect will be that of common white light; as the two bright col- 
ored disks produced in the field of a microscope by a double 
image prism and a selenite plate, become white where they over- 
lap. The effect is best studied with the binocular microscope and 
Polariscope. A plate of selenite is introduced so as to give both 
fields of a bright conspicuous color; and then a film of mica is 
tnterposed in the course of the rays supplying one tube, of such 
thickness and position as to give, by retardation, a color as nearly 
aS Possible complementary to the first. One field, for instance, 
may be a bright red, and the other a bright green, while the 
observer, viewing both at once, will see only a colorless field. By 
an ingenious changing of the plates by which the colors are 
Produced, both fields may be gradually changed to totally different 
colors, the complementary character being maintained throughout 
the change, without any knowledge of the change on the part of 
the observer. If the color of one field is entirely removed, the 
observer becomes slowly and feebly conscious of the color of the 
other. The optical and physiological bearings of this discovery 
are obvious and interesting. , 
: New Arrangement or Spring Curps.— Miller Bros., of 1223 
Broadway » N. Y.. are manufacturing a contrivance which must be, 
rrian purposes, a very nient substitute for Dr. Maddox’s 
“Pring clips. It consists essentially of a mahogany strip, of 
grooved upon its upper surface and protected with 
