326 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



denser ; moreover, the two inner lenses of the condenser are movable, 

 and are controlled by two knobs, as shown in the diagram. This 

 adjustment of condenser lenses removes chromatic aberration, and the 

 rays of light emerge in moderate convergence. As ordinarily employed 



Fig. 52. 



for direct projection from tbe preparation, the apparatus consists of the 

 optical bench, with the following parts : — 



1. A large cooling-cell, kept cool by a current of running water. 



2. The bellows, with tube. 



3. The Microscope condenser (especially needed when high powers 

 are employed, say fW to yW) and diaphragm holder (sufficient for low- 

 power work ; a small rack-and-pinion suffices for adjustment. 



4. The object-stage and small cooler. The preparation rests on the 

 cooler, and protection from heat is thereby afforded to the most delicate 

 specimens ; the adjustment of the object permits any desired part to be 

 brought accurately into the field. 



5. The objective-carrier, with triple nose-piece, a broad projection- 

 tube, and a diaphragm for the purpose of narrowing the broad tube. A 

 narrow tube, which screws into the broad one, permits use of oculars 

 if desired ; the adjustments are by rack-and-pinion and micrometer screws. 



6. Wooden cover, with cloth curtain, which fits over the diaphragm- 

 carrier, stage, and objectives, to shield off any light which might escape 

 at the sides. 



