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 105 x 105 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 Abbe 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 Abbe 

 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 



