222 



THE PROJECTION 7 MICROSCOPE 



[CH. IX 



FIG. 121. PROJECTION MICROSCOPE. 



/, 2 Feeding screws of the arc lamp, 

 j Set screw for the upper carbon. 



4 Set screw for holding the stem of the arc 

 lamp in the socket on block i. 



5 Set screw for the lower carbon. 



Hc-\r The horizontal, upper carbon. It 

 must be made positive (+). 



L The source of light, i. e., the crater of 

 the upper carbon. 



Vc The vertical or lower carbon. It is 

 negative ( ). 



Axis, Axis, Axis The principal optic axis 

 from the positive crater of the arc lamp 

 extending through the condenser, the stage 

 water-cell, and the microscope to the screen. 



i Condenser 2 The triple condenser for 

 receiving and concentrating the light from 

 the crater of the arc lamp. 



1 The first element of the condenser which 

 renders the diverging light parallel. It con- 

 sists of a meniscus next the light and a 

 plano-convex lens (compare fig. 105, in). 



2 The second element of the condenser 

 which concentrates the parallel beam. 



W Water-cell between the two plano-con- 

 vex lenses in the parallel beam of light. 



As a projection microscope uses ob- 

 jectives of shorter focus and smaller 

 diameter than the magic lantern, 

 greater care must be exercised in get- 

 ting all the elements, radiant, con- 

 denser and projection objective, cen- 

 tered along one continuous line or 

 axis, and in having the different ele- 

 ments the right distance apart. 



