ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
39 : 
MICROSCOPY. 
a. Instruments, Accessories, &c.* 
Euess’s Petrological and 
Crystallographic Micro- 
scopes.! — Herr R. Fuess 
has introduced several im- 
provements into his Petro- 
logical Microscope, which 
now has the form given in 
fig. 36. 
The object-stage is fitted 
for fine measurements. The 
scale is graduated in half 
degrees and two verniers 
read to minutes. The 
stage-plate has a toothed 
edge and is rotated by 
means of a pinion a, which 
can be thrown out of gear 
by the lever Ji. A mechani- 
cal stage is applied on the 
rotating stage - plate. By 
one of the rectangular 
movements effected by the 
screw S an interval of 
0 * 01 mm. can be indicated. 
The other screw S' has a 
more rapid thread to en- 
able the preparation to be 
quickly passed across the 
field of view. The mirror 
slides vertically on an arm 
which can be rotated to 
one side. The polarizer 
has a rack - and - pinion 
movement. A conical stop 
fitting into corresponding 
slots in the socket deter- 
mines the position of the 
nicol for 0°, 45°, and 90°. 
An iris-diaphragm can be 
inserted beneath the nicol. 
A condensing lens of great 
focal length atttached to 
the polarizer serves for the 
(1) Stands. 
* This subdivision contains (1) Stands ; (2) Eye-pieces and Objectives ; (3) lliu- 
minating and other Apparatus ; (4) Photomicrography ; (5) Microscopical Optics 
and Manipulation ; (6) Miscellaneous. 
f Zeitschr. f. Wiss. Mikr., vii. (1890) pp. 177-87. 
