THE MICROSCOPE AND CELL-STRUCTURE. 



59 



94. Compound Microscope. The simple microscope can 

 be used for all purposes where a magnification of not more 

 than 20 diameters is required, and is an extremely convenient 



instrument for this low- 

 power work. When higher 

 magnification is desired, 

 we must use the com- 

 pound microscope, in 

 which the image of the 

 object is obtained by one 

 lens (or a set of lenses) 

 called the objective, and 

 this image is magnified 

 by a second lens, the eye- 

 piece. The objective is 

 screwed into the lower 

 end of the brass body- 

 tube, which is blackened 

 inside (why?); the objec- 

 tive consists usually of 

 several lenses screwed to- 

 gether. The eyepiece, 

 which magnifies the in- 

 verted image of the object 

 produced by the objective, 

 consists of two lenses, the 

 one next the observer's 

 eye being called the eye- 

 glass and the lower one 

 the field-glass. 



In the cheaper form 

 (Fig. 30) the tube which 

 carries the lenses is moved 

 up and down, to bring the 

 objective near the object 

 Fig. so. Compound Microscope with sliding and thus bring the latter 



Coarse Adjustment. ^^ ^ focug> ingide 



another tube fixed to the 



stand ; this is called the " sliding coarse adjustment." In 

 the more expensive microscopes (Fig. 31) there is a rack-and- 

 pinion movement for raising or lowering the body-tube. The 



