THE MICROSCOPE 



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PRACTICAL DIRECTIONS. 



General Structure of the Compound Microscope— The com- 

 pound microscope, with which you must now become acquainted, 

 consists of a strong sland (Fig. 37, a) 

 from which rises a vertical pillar (b). 

 To the latter are attached — a horizontal 

 plate or stage (c), perforated in the cen- 

 tre with an aperture (d), the size of 

 which can be varied by means of a 

 diafhragm: an adjustable mirror (e), 

 placed below the stage : and a vertical 

 hih {/) attached above the stage by a 

 horizontal arm. Two combinations Oi 

 lenses are used : an objective or object- 

 glass (/i), consisting 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 (2), consisting 

 of a metal cylinder with a lens at each 

 end, which slides into the upper end of 

 the tube. It is this arrangement of 

 lenses which forms the essential feature 

 of the compound microscope : the ob- 

 ject, placed on the stage, is magnified 

 by the objective, and the magnified 

 image, thrown into the interior ot the 

 tube, is further enlarged by the ocular. 

 The object h brought into jocus — i.e., 

 placed at such a distance from the 

 objective that a perfectly clear and well- 

 defined image is obtained — in one ot 

 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 move- 

 ment forms the coarse adjustment. In addition, all good microscopes 

 have - a Jine adjustment, usually consisting of a spring concealed in the 



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Fig. 37.— Diagram of compound 

 microscope. 

 rt, stand ; b. pillar; b\ moveable 

 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 ; 

 i. ocular ; k, screw of fine 

 adjustment. 



