VII 



THE MICROSCOPE 



119 



PRACTICAL DIRECTIONS 



General Structure of the Compound Microscope. The 



compound microscope, with which you must now become 

 acquainted, consists of a strong 

 stand (Fig. 37, a) from which 

 rises a vertical pillar (b) , To the 

 latter are attached a horizontal 

 plate or stage (c} } perforated in 

 the centre with an aperture (d), 

 the size of which can be varied 

 by means of a diaphragm ; an 

 adjustable mirror (e), placed be- 

 low the stage : and a vertical 

 tube (/) attached above the stage 

 by a horizontal arm. Two com- 

 binations of lenses are used ; an 

 objective or object-glass (h), con- 

 sisting of a metal tube with two 

 or more lenses fixed into it, 

 which screws into the lower end 

 of the tube : and an ocular or eye- 

 piece (?'), consisting of a metal 

 cylinder with a lens at each end 

 which slides into the upper end 

 of the tube. It is this arrange- 

 ment of lenses which forms the 

 essential feature of the com- 

 pound microscope : the object, 

 placed on the stage, is magnified 

 by the objective, and the mag- 

 nified image, thrown into the 

 interior of the tube, is further 

 enlarged by the ocular. 



The object is brought into focus 

 i.e., placed at such a distance 

 from the objective that a per- 

 fectly clear and well-defined 

 image is obtained in one of two 

 ways. The tube can be raised 

 or lowered either by sliding it up 



and down in an outer tube or collar (g), or, in the more 

 expensive instruments, by a rack and pinion : this movement 

 forms the coarse adjustment. In addition, all good micro- 



FIG. 37. Diagram of compound 



microscope. 



a. stand ; b. pillar ; b' movable 

 portion of pillar, raised and 

 lowered by fine adjustment ; 

 c. stage ; d. aperture in stage ; 

 e. mirror ; /. tube ; /' milled 

 ring for raising and lowering 

 tube; g. collar; h. objective; 

 . ocular ; k. screw of fine 

 adjustment. 



