le 
a a 
COMPOUND MICROSCOPES 13 
embodies only those parts which are most essential for the 
examination of powdered drugs, bacteria, and_ urinary 
sediments. This microscope is provided with a stage of the 
dimensions 105x105 mm. This factor and the distance of 
80 mm. from the optical centre to the handle arm render it 
available for the examination of even very large objects and 
preparations, or preparations suspended in glass dishes. The 
stand is furnished with a side micrometer, a fine adjustment 
having knobs on both sides, thereby permitting the manipula- 
tion of the micrometer screw either by left or right hand. The 
illuminating apparatus consists of the Abbé condenser of numeri- 
cal aperture of 1.20, to which is attached an iris diaphragm for 
the proper adjustment of the light. A worm screw, mounted 
in connection with the condenser, serves for the raising and 
lowering of the condenser, so that the cone of illuminating 
pencils can be arranged in accordance to the objective employed 
and to the preparation under observation. *The objectives 
necessary are those of the achromatic type, possessing a focal 
length of 16.2 mm. and 3 mm. Oculars which render the best 
results in regard to magnification in connection with the two 
objectives mentioned are the Huyghenian eye-pieces II and IV 
so that magnifications are obtained varying from 62 to 625. 
It is advisable, however, to have the microscope equipped with 
a triple revolving nose-piece for the objectives, so that provision 
is made for the addition of an oil-immersion objective at any 
time later should the microscope become available for bac- 
teriological investigations. 
THE RESEARCH MICROSCOPE 
The research microscope used in research work (Fig. 17) must 
be equipped more elaborately than the microscope especially 
designed for the use of the pharmacognosist. While the simple 
form of microscope is supplied with the small type of Abbé 
condenser, the research microscope is furnished with a large 
illuminating apparatus of which the iris diaphragm is mounted 
on a rack and pinion, allowing displacement obliquely to the 
optical centre, also to increase resolving power in the objectives 
when observing those objects which cannot be revealed to the 
best advantage with central illumination. Another iris is 
