Ch. VI] 



THE PROJECTION MICROSCOPE 



203 



it is in focus, the objective not being moved. Of course this means 

 that the stage must be separately movable (fig. 109). See also 

 §296. 



§ 316. Demonstrations with a vertical projection microscope. — 

 Many specimens must be mounted in liquids and cannot be set in a 

 vertical position; therefore the microscope must be vertical and the 

 object remain horizontal. In such a case project the light from 



Fig. 123 A, B. Metal Hood over the Objective to Aid in Centering the 



Light. 



(From Optic Projection). 



A Longitudinal section of the objective to show the metal hood. 



B End view of the objective with the crater of the arc lamp directly in the 

 center at the left and to one side of the center at the right. The adjustments, 

 YA,LA in fig. 122 are to enable one to center the light easily. 



the large condenser (fig. in) or from the small arc lamp (fig. 49) 

 upon the mirror of the microscope and reflect it directly upward, 

 and then use a mirror or prism to change the direction from vertical 

 to horizontal. (See fig. 109, 114, to recaU how the beam is changed 

 in direction 90°.) 



A most striking preparation is one of the hay infusion (§211) 

 projected upon the screen. A water immersion objective of 2 to 3 

 mm. equivalent focus is excellent for projecting such preparations. 



Demonstration Lantern and Table for Artificial Daylight 



§ 316. Special microscopic demonstrations. — As stated above, 

 if one is to see the finest details of structure there is no satisfactory 

 way but to look into the microscope direct. There is also in every 

 laboratory for microscopic work considerable waste space if depen- 



