APPARATUS AND METHODS. 



convenient instrument for this low-power work. When 

 higher magnification is desired we must use the compound 



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 ob- 

 jective consists usually 

 of several lenses screwed 

 together. The eye- 

 piece, which magnifies 

 the inverted 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. 6) the tube which 

 carries the lenses is 

 moved up and down, to 

 bring the objective near 

 the object and thus bring 

 the latter clearly into 

 focus, inside another 

 tube fixed to the stand ; 

 this is called the "slid- 

 ing coarse adjustment." 

 In the more expensive microscopes (Fig. 7) there is a rack- 

 and-pinion movement for raising or lowering the body- 

 tube. The coarse adjustment brings the outlines of the 



Fig. 6. Compound Microscope with sliding 



coarse adjustment. 



A, eye-piece ; B, draw-tube ; C, body-tube ; 

 D, adjustment ; B, objective ; F, stage. 



