CH. I] 



MAGIC LANTERN WITH DIRECT CURRENT 



28. See if the lantern is centered. Make sure that the 

 different elements of the lantern are centered along one longitudinal 

 axis (fig. 1,2). Then and then only will a perfect screen image be 

 produced. If the apparatus was installed correctly in the begin- 

 ning the only part liable to be out of line is the crater of the positive 

 carbon. In burning the carbons frequently so wear away that the 

 crater is at one side of the axis. Slight decentering of the crater 

 can be easily corrected by using the fine adjustment designed for 

 the purpose ( 10, fig. 3, see also Troubles 79). 



29. Slide-carrier. Be sure that the slide-carrier works 

 properly and easily. The "push-through" form (fig. 6), is very 

 convenient, for while one slide is on exhibition the one previously 

 shown can be removed and another put in place, and it can be 

 instantly put in front of the condenser when the lecturer signals. 



FIG. 6. "PUSH-THROUGH" OR DOUBLE SLIDE-CARRIER. 



/ The frame which remains in one position in front of the condenser and 

 serves as a container and guide for the "push-through" part. 



2 The movable slide-holder or "push-through" part of the carrier. It 

 moves easily to the right and to the left. It contains two slides in the proper 

 position for an erect image on a vertical opaque screen (see fig. 7,8}. 



3 3 Notches in the movable part to enable one to grasp the slide easily. 



4 Elevator serving to lift the slide when at either end. In some forms the 

 elevator lifts the entire slide from the middle instead of tilting one end. 



5 6 Inclined planes at each end. These raise the elevator when the carrier 

 is moved to either end of the base. 



S i Lantern slide in the carrier in front of the condenser. 



S 2 Lantern slide in the carrier at the left end. It is of the first magic 

 lantern (1665) and is in position to be removed or to be pushed to the right for 

 exhibition. 



30. To start the arc light. Turn on the current by closing 

 the switch (fig. 1-4). If the lam]) is of the automatic type the 



