CH. IX] 



PROJECTION MICROSCOPE 



255 



condense it either upou the object for lantern slides and low objectives, 

 or it narrows the light into a cone of the proper size for further con- 

 centration by the achromatic condenser (§412). One of the most 

 used, and also one of the best condensers for the arc lamp is composed 

 of two plano-convex lenses with their convex sides facing each other. 

 There is then one plane face next the radiant and one toward the mi- 

 croscope. The lens next the radiant is somewhat smaller than the 

 other. Both are loosely mounted to allow for expansion and the cell 

 in which they are mounted should be freely ventilated. This con- 

 denser should be adjustable back and forth and up and down. 



Fig. 206. 



Fig. 206. Arrangement and Centering of the Radiant [Leiss) . 



In (/) The radiant, i. e., the crater (Fig. 205) is too far to the right ■ 



(2) The crater is too far to the left ; 



(3) The crater is too high ; 



(4) The crater is too lozv ; 



( 5) The crater is too far from the lamp condenser ; 

 ( 6-7) The crater is too near the condenser. 



(5) The crater is in the correct position. 



As pointed out m the explanation of Fig. 205, there may be a slight central 

 shadow with soft cored carbons when the lamp and condenser are in the best relative 

 position. 



§411. Water Bath for Removing Heat. — This is a cell of 

 some kind with plane glass faces. It should be approximately of a 

 size to allow the light to pass through a stratum of water 50 mm. 

 thick. Even this will allow something over 2% of the heat to pass. 

 It is a great advantage to have cool or cold water circulate through this 

 constantly. 



