MICROSCOPES FOR USE IN CHEMICAL LABORATORIES 69 
The coarse adjustment R by rack and pinion serves to roughly 
focus both tubes at once; then each objective is focused sepa¬ 
rately by means of the fine adjustment screw collars F, just 
above the objectives. That really satisfactory results may be 
obtained it is essential that both the sets of eyepieces and objec¬ 
tives shall be paired, i.e., shall have been constructed for use 
with a comparison microscope and be exactly equivalent in all 
properties. The fields are flat, brilliant, and with careful illu¬ 
mination and adjustment and a little practice most excellent 
results can be obtained. The instrument is adapted to all 
problems involving an exact comparison of size, structure or 
symmetry of microscopic objects, especially where the structure 
is so intricate as to render comparison and interpretation with 
the ordinary single compound microscope exceptionally difficult 
without recourse to photography. The value of the instrument 
in all problems of forensic chemical microscopy is evident. 
A second type of comparison microscope^ is provided with a 
single eyepiece only, the field being divided into halves. As in 
the previously described instrument, two microscope tubes are 
attached to a single pillar and both focused together by rack 
pinion. Attached to the tubes is a rectangular closed chamber 
of the Inostranzeff type provided with two sets of totally refiect- 
in prisms, thus yielding to a single eyepiece half the field of 
view of each microscope. By means of a knob in the side of 
the chamber one set of prisms may be shifted at will so as to cut 
off the field of one instrument. 
In addition to a single fine adjustment, simultaneously affect¬ 
ing both microscopes, each tube is provided with independent 
fine adjustment collars just above the objectives. A single 
stage with two openings carries two substages, each with an 
Abbe condenser and with a mirror. The instrument may be 
employed with polarized light, thus affording exceptional 
opportunities for exact comparisons in the search for food 
adulterants and in microchemical analysis. Since in this in¬ 
strument we have a single ocular yielding a divided field, it is 
possible to obtain photomicrographs, half the area of the circle 
^ W. and H. Seibert, Wetzlar, Germany. Thorner, Chem. Ztg., 36 , 781. 
