202 



THE PROJECTILV UfCROSCOPE 



[Ca. VI 



carefully centered, the centering will vary slightly with the burning 

 of the carbons. To compensate for this there must ?3e fine adjust- 

 ments to raise and lower the carbons and to move them from side to 



Fig. 122. Projection Apparatus Showing the. Parts and the Wiring for 



an Arc Lamp:. 



(From Optic Projectibn).. 



Tiie Objective, Condenser, and Arc Lamp are «m separate blocks which move 

 independently along the optical bench (fig. 131-). 



( c Center of the objectives where the rays from the condenser should cross. 



i, 2 The first and second elements of the three lens condenser with a water 

 cell'for absorbing radiant heat between the lenses. 



V The ventilating hood of the lamp house. 



LA , VA The mechanism for fine adjustment of the arc lamp to the sides and 

 vertically. These are a necessity for projecting with the microscope, otherwise 

 the crater cannot be kept centered. 



FS The fine adjustments for the two carbons. 



PWR Separable attachment for the wires from the outlet box to the table 



switch. 



Wi Wire from the table switch to the upper carbon. 

 Ws Wire from the table switch to the rheostat. 

 11 j Wire from the rheostat to the lower carbon. . 



side. No good projection can take place unless the full cone of 

 light shines upon the end of the objective. 



To get the very best effect in the easiest way there should be a dull 

 black shield over the end of the objective (fig. 123) so that the image of 

 the crater can be seen without hurting the eyes. When the crater is 

 focused on the end of the objective the specimen is moved up until 



