260 O. N. Rood on production of Lustre. 
arrested in about twenty seconds, or in the ;',th portion of the 
time it otherwise would have occupied. 
Art. XXX.—Description of a simple apparatus for producing 
lustre without the use of Lustrous surfaces or of the Stereoscope; 
by Prof. OepEN N. Roop, of Columbia College. 
In attentively looking at plane polished surfaces of aventurine 
glass, I have often been for a moment unable to dee 
binocular vision exactly where some of the imbedded cryst 
minute © : the 
triangular apertures, were punched. Directly below this on 
blackened surface of the floor of the box, were sprinkled about® 
hundred small pieces of white, red, and green paper, each being 
h 
construction, light of different intensity or color was pres? 
to the two eyes pe rforated 
If now a second blackened diaphragm of brass foil, pyr 
with many minute triangular apertures, carefully prepare 
not to have an indented surface, be placed above the first 
apertures, at a distance of 1 or 1 of an inch, brilliant po! 
light are seen either by one eye or the other, light from the ible 
opeting rarely reaching both eyes. It now becomes 1Mp" geet 
to decide on the location of these points, and they often bat 
suspended in space, somewhere in the interior of the box, 
exactly where the observer cannot determine. — 
Some Fa Sel 
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