For long continued work on any one subject artificial 

 light has one advantage over daylight in that it is con- 

 stant in quality and intensity. The best artificial light 

 is a Welsbach burner. A whitened incandescent bulb 

 is good. Ordinary lamplight can be used very success- 

 fully. In using artificial light it is best to use a bull's eye 

 condenser between it and the mirror. It is also best, 

 wherever possible, to use a blue glass between the light 

 source and the specimen. Some workers make a glass 

 globe filled with ammonia copper sulphate serve the 

 purpose of both the condenser and the blue glass. It is 

 so mounted in a shade as to exclude all other light from 

 the microscope. An eye shade, or some shade cutting 

 off all light from the microscope excepting that which 

 strikes the mirror, is often desirable. 



FOCUSING 



After seeing that an objective (low power) and an ocu- 

 lar are in place put a transparent or semi-transparent 

 specimen on the stage, swing the mirror bar to the me- 

 dian line, take hold of the edge of the mirror and adjust it 

 so as to illuminate the object as evenly as may be judged 

 by looking directly at it. 



Focus the body tube down by means of the coarse 

 adjustment until the objective nearly touches the cover 

 glass, being careful not to touch it. Then with the eye 

 at the eyepiece, focus up carefully with the coarse ad- 

 justment until the specimen comes plainly into view. 

 Be careful not to pass by this focal point without notic- 

 ing it. This is likely to occur if the light be too intense 

 and the specimen thin and transparent. If the sliding 

 tube coarse adjustment is used, focus carefully by giving 

 the tube a spiral movement. 



When the object is brought fairly well into focus by 

 means of the coarse adjustment use the fine adjustment 

 14 



