a a a a ees kena ee eee 
MICROSCOPY. 441 
edge, it will not be reflected out of its plane, while the rays B and 
C, entering the left side of the prism, reach the inclined faces, 
from which they are reflected to the opposite lower one, and are 
changed in their course to the right, from here again reflected, to 
emerge at the corresponding opposite point. Fig. 3 is a perspec- 
tive representation of the prism. — Journal of the Franklin Insti- 
* 
SrerHenson’s Brnocurar.— Mr. Stephenson has reported to the 
Royal Microscopical Society, some improvements in his erecting 
binocular microscope. The lower prisms by which the light is 
divided and the image laterally inverted, are made smaller than 
before and placed nearer to the back combination of the objective. 
They are now made .68 in. long, .412 in. wide, and .2 in. thick ; 
and are inclined to each other at an angle of 42°, making the 
angular divergence of the bodies 93°, and the distance of the 
point towards which the eyes converge nearly fifteen inches. The 
prisms of this size are mounted in a small tube which projects 
beyond the nozzle of the instrument, and into the mounting of 
the objective nearly to the posterior combination of glasses. The 
quantity of glass in the prisms is greatly reduced, and powers as 
high as 4 in. may be easily used. The standard length of body is 
, Secured: and also an easy convergence of the eyes. 
By altering the angle of inclination of the bodies to the perpen- 
dicular from 75° to 664° the use of a Nicol’s prism as an analyzer, 
which is quite unsatisfactory in a binocular, is easily dispensed 
with. When polarized light is used the box containing the upper 
Prisms (the original upper prism being now made in two parts ) 
'S withdrawn and an analyzing plate of highly-polished glass 
substituted, reflecting the light at the polarizing angle of 567, 
and Securing more light and improved definition. 
it desired, the upper prisms may be likewise replaced by a plane 
mirror silvered by the beautiful process employed by Mr. Browning 
in the manufacture of his reflecting astronomical telescopes. Thus 
bak Set rid of all the glass and of two surfaces, but obtain an 
Meomplete reflection and a less permanent reflector. 
Opaque ILLUMINATION UNDER Hren powers.—H. A. Johnson, 
M.D., President of the State Microscopical Society of Ill., com- 
oo to that society another method of producing this 
—<ult effect. He employs Prof. H. L. Smith’s plan of making 
{iF ARSE lta PORN +: 
* We are indebted to the Journal for the use of the above cuts. 
