i^o. 640] SHORTER ARTICLES AND DISCUSSION 479 



D.C.. placed so that the distance between the uprights carrying 

 the projector and the microscope table is 20 inches, while half- 

 M^ay between the projector and the microscope a water cell is 

 placed for the absorption of heat ravs. The projector has a 

 movable condenser of its own. The position of this condenser 

 influences the intensity of lifrht. Our table is made for such a 

 position of this condenser that the light on the toeusnur screen 

 is biightest It IS not th( ^\mo foi (\er> objt iii 1 imi-l be 



found by experimenting, with the aid ot an assisiiiiit. wlio nicvcs 

 the condenser while the observer watches tlio field. loi' this 

 experiment the microscope substage is best low(M-ed about 2 mm. 

 to insure even illumination. "When the position of tlie condenser 

 of the projector has been found and marked on the mounting, 



