APPAKATUS AND METHODS. 7 



the body-tube ; the nose-piece carries the two objectives, 

 and by rotating it we can quickly change from low to high 

 power and vice versa. 



6. Notes on Use of Compound Microscope. If the 



stand is without rack and pinion, see that the tube moves 

 easily, but not too easily, up and down ; if stiff, take out 

 the tube, rub it with a little olive oil or vaseline. 



See that the lenses are clean ; dust the mirror, adjust it 

 so as to send light through the body-tube, and insert first 

 one eye-piece and then the other. Rotate each eye-piece ; 

 if any specks are seen to rotate with it, they must be on the 

 eye-piece lenses, and should be removed with a chamois 

 leather or soft cloth. If the specks are dim, the dirt must 

 be 011 the objective ; wipe the latter very carefully, and if 

 necessary wash its front lens with a jet of water from a 

 wash-bottle and wipe it dry. Do not rub lenses much, or 

 unnecessarily ; do not unscrew the separate lenses of a high 

 objective unless it becomes absolutely necessary, and then 

 do it with great care ; in cleaning the lenses do not remove 

 the black coating on the inside of the tube. 



Always use the low-power objective first, and never use the 

 high power unless the object is covered with a cover-glass. 



With the low power use the flat mirror and a large hole 

 of the diaphragm below the stage; with the high power use 

 the concave mirror and a small diaphragm, otherwise 

 (though the field may look brighter) the outlines of the 

 cells, etc., will not be so sharply defined. 



Never use the fine adjustment until the focus has been 

 obtained with the coarse adjustment, whether by sliding or 

 by rack and pinion. With the low-power objective (the 

 one with the larger front lens) , slide or rack down the tube 

 to about J inch from the object; then, looking through the 

 eye-piece, slide or rack the tube upwards till the object 

 comes into view, and focus clearly by turning the milled 

 head of the fine adjustment screw to right or left. With 

 the high power lower the tube to about J inch from the 

 object, then very carefully slide or rack the tube down 

 while looking through the eye-piece, till the object just 

 becomes visible, and focus with the fine adjustment. 



