OZ THE MICROSCOPE AND CELL-STRUCTURE. 



95. Notes on Use of Compound Microscope. If the 



stand is without rack-and-pinioii, 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 

 eyepiece and then the other. Rotate each eyepiece ; if any 

 specks are seen to rotate with it they must be on the eyepiece 

 lenses, and should be removed with a chamois leather or soft 

 cloth. If the specks are dim, the dirt must be on the objec- 

 tive ; 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. 



Never use direct sunlight, and also avoid using artificial 

 light. The best light is that reflected from white clouds in a 

 northern sky. If a south aspect is the only one available, 

 direct sunlight must be cut off, by using a white blind or 

 fitting a piece of white card on the mirror. 



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 i inch from the object; then, looking through the 

 eyepiece, 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 eyepiece, till the object just becomes visible, and focus 

 with the fine adjustment. 



