INTRODUCTION. 



B 



The Microscope. The compound microscope consists of an eye-piece 

 or ocular A and of an objective B placed at opposite ends of the body of 

 the instrument. The eye-piece tits into the draw-tube, which forms part 

 of the body, and by means of 

 which the distance between 

 the eye-piece and objective 

 can be adjusted. The body C 

 is carried by the pillar D and 

 is moved in the direction of its 

 axis by means of a friction 

 tube or (Fit;. 1) a rack and 

 pinion, actuated by the milled 

 head F for coarse adjustment 

 and by the milled head F' for 

 fine adjustment. Beneath is 

 the stage S, and beyond this 

 the illuminating appliance, 

 which consists of a double 

 mirror M, one side of which 

 is plane and the other con- 

 cave. Between the mirror and 

 the stage is the adjustable 

 sub-stage I which carries the 

 diaphragm, for regulating the 

 quantity of light admitted to 

 the object, and for which 

 a condenser may be easily 

 substituted. The latter, which 

 may be termed an inverted 

 objective, is employed to pro- 

 duce a more exact and powerful 

 concentration of light upon 

 the object than can be ob- 

 tained with the concave mirror alone 

 less than ^ in. or 4 mm focal distance. 



The student will require for work in the histological class an instrument 

 yielding magnifications of from 50 to 350 or 400 diameters. He will 

 obtain this by means of a H in. Huyghenian ocular and objectives of 1 in. 



and is required with powers of 



