ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
387 
Fig. 40. 
of considerable size is inordinately heavy. A is the objective which 
forms an image near B, which is composed of two lenses, of which one 
is achromatic. This arrangement is essentially like a terrestrial or 
erecting eye-piece for a telescope, except that in the terrestrial eye-piece, 
the crossing-point (Kamsden circle) 
is between the component lenses, 
whilst in this binocular the crossing- 
point is situated higher up, in fact, 
just at the angle-edge of the achro- 
matic prism C, where the pencil is 
divided. This arrangement gives a 
good field in each eye-piece. After 
division, the pencils pass on to the 
two eye-pieces D D, where they 
form images which are slightly un- 
symmetrical, by which the stereo- 
scopic effect is obtained. 
The diagram fig. 39 is from a 
drawing made for this Journal by 
the late A. Prazmowski. 
Verich's (fig. 40) is, so far as 
its essential optical arrangement is 
concerned, identical with that of 
Tolies, having a central equilateral 
^rism and two truncated ones at the 
sides. The erector is, however, an 
achromatic combination formed of 
a lower plano-convex lens and an 
upper biconvex one. The central 
equilateral prism is also mounted 
with its lower face in a brass ring, 
having a circular diaphragm about 
1/4 in. in diameter immediately 
above the upper lens of the erector. 
To secure its exact orientation in 
relation to the truncated lateral 
prisms, the brass ring is made to 
rotate partially in the horizontal 
plane ; a portion of the cylindrical 
edge of the ring being provided 
with a “ worm ” on which acts an 
endless screw that can be turned by 
a small key whilst the observer 
views the image. 
Fig. 41 shows the mechanism by 
which the lateral prisms (with the 
eye-pieces) can be separated to suit 
the width of the observer’s eyes. 
The sliding ebonite box-fittings in which they are mounted are attached 
respectively to the diagonal racked bars ; the revolution of the toothed 
pinion (acted upon externally by the milled head shown by a dotted line 
2 E 2 
