ta a 
Description of New Optical Instruments, viz.: 1. Polarizing 
Spectacles. 2. Picture Polariscope. 3. Polarizing Dia- 
phragm for the Microscope. 4. Surgical Polariscope. By 
ALEXANDER Bryson, Esq. Communicated by the Au- 
thor. 
1. Polarizing Spectacles. 
By the aid of this instrument, the naturalist, engineer, or 
salmon-fisher, is enabled to distinguish objects beneath the 
surface of the water. It consists of a pair of Nicol’s prisms, 
so adapted as to prevent the transmission to the eye of the 
horizontally polarized ray reflected from the surface of the 
water, and thus to destroy the glare which prevents the light 
from penetrating below the surface. When the surface of 
the water is smooth, and the instrument so arranged as to 
form an angle with the water of 52°, the effect is complete ; 
at other angles, half of the incident ray passes through the 
prisms. The prisms are fitted into common spectacle frames, 
or used in the hand like a double opera-glass. When used 
by the engineer, for examining the bottoms of rivers or canals, 
where the water is sufliciently clear to admit the reflected 
rays from the bottom to permeate, and where the depth is 
known, the terminal planes of the prisms can be modified so 
as to destroy the effect of the refraction of the water, and ex- 
hibit the objects at the bottom in their true places. 
The prisms used are those last invented by Mr William 
Nicol, as they give a larger field of view than those formerly 
described in this Journal. The angles being 71° and 93°. 
2. Picture Polariscope.* 
This instrument is the same in construction as the preced- 
ing, except that the prisms are placed so as to prevent the 
admission of a perpendicular instead of a horizontal polarized 
* Since this instrument was constructed, I find I have been anticipated in 
this application of Nicol’s prism by Professor Dove of Berlin. 
