CH. IX] 



COMBINED PROJECTION 



293 



apparatus. This tube has a set screw in the side to hold the post 

 at any desired level (fig. is8F). In order to be able to perfect the 

 centering of the apparatus, the screw holes in the flanges are made 

 larger than the screws so that by loosening the screws the flange 

 can be shifted slightly from side to side. If necessary one can use 

 washers to increase the size of the screw heads, so that the holes 

 in the flange can be quite large. 



431. Wooden shields for holding objectives, etc. For hold- 

 ing projection objectives of low power, shields of thin board (i to 



FIGURE 158?. SECTIONAL VIEW OF A RAILING FLANGE AXD SOCKET. 



/ The flange in section. The screw holes are made large for centering. 

 5 The set screw to hold the post in place. 



p Post extending down into the socket. It is held at any desired height 

 by the set screw (s). 



sc Socket for receiving the post or stem of any piece of apparatus. 



\ l /2 cm., l /2 in. thick) can be used, and a post or stem of iron made 

 from a bolt by hammering out the end in the form of a fan (fig. 

 i58A). To aid in centering, the screw holes in this post should 

 also be larger than the screws. 



MICROSCOPE AND LANTERN-SLIDE PROJECTION COMBINED 



432. With an outfit of the lathe-bed type (fig. 138), it is very 

 simple to change from lantern-slide to micro-projection and the 

 reverse. All that is necessary is to put the lantern-slide carrier 

 next the condenser, and the lantern-slide projection objective on its 

 block in position. The stage and the microscope must be set off 

 the track on the table. The only difficulty is that the second ele- 

 ment of the condenser for the micro-projection is of too short a 

 focus for most lantern-slide projection. This can be overcome in 



