MEMORANDA. 167 
picture (with 2500 diameters) appear hexagonal, but reveal 
their true structure under a lens; in the large are quite 
distinctly circular, but will assume an hexagonal appearance 
if reduced by a concave lens of sufficient power, or even by 
mere distance. 
If these pictures appear good enough to give interest to the 
above statements, I beg you to give a place to this communi- 
cation in the pages of your valuable Journal.—J. J. Woop- 
warp, M.D., Assistant-Surgeon and Brevet-Major U.S.A., 
in charge of the Record and Pension Division, Surgeon- 
General’s Office, and of the Medical Section, Army Medical 
Museum. 
Light Reflected from Transparent Surfaces.—At present this 
subject, being one of interest in relation to recent binocular 
arrangements, I beg to record some notes. Selecting a few 
examples of the amount of light reflected from the surface of 
crown-glass, having a refractive index of 1°525, they range as 
follows : 
Quantity of light 
Angle of incidence. reflected from 
1000 of incident rays. 
GP vk eed eg, ete 
Re ee al a tok vee oe OO 
Dee Pitta he a ew GO 
| (eigenen iiss beaded | aed Ye: 
These examples are taken within the limits of useful applica- 
tion, and show the small quantity of light really obtainable 
from crown glass such as is used for prisms. It consequently 
became a consideration to ascertain what increase would re- 
sult from the use of dense flint glass of a high refractive 
power. Certain formule have been given for this which 
claimed a very promising result, but which is scarcely con- 
firmed by experiment. Mr. Huggins kindly undertook to 
try this, being possessed of very perfect photometric appa- 
ratus, and as I had suggested that the dense glass prisms of 
a spectroscope might have their numerous surfaces coated 
with a thin film of albumen, with the view of lessening the 
quantity of reflected, and consequently increasing the amount 
of transmitted, light (which theoretically it should do, as the 
refractive index of albumen is nearly as low as that of water). 
The following is his letter to me, dated April 16th: 
“ Dear Sir,—On Friday evening last I tried the reflection 
from different transparent surfaces, and found the difference 
