TROUBLES WITH THE MAGIC LANTERN 



[CH. I 



60. Centering the vertical objective. After the horizontally 

 placed condenser lens is centered the objective is placed in a vertical 

 position over it and moved sidewise until the cone of light enters 

 the middle of the first face and leaves the middle of the last face of 

 the objective. One proceeds exactly as for centering it in the 

 horizontal position ( 55, 58). Just over the objective is placed a 

 45 degree mirror silvered on the face, or a right-angled prism, to 

 direct the vertical rays horizontally to the screen (fig. 16). The 

 lower mirror may be an ordinary glass mirror silvered on the back, 

 but the mirror over the objective must be silvered on the face to 

 avoid a duplication of the image. 



TROUBLES: HOW TO AVOID AND HOW TO 

 OVERCOME THEM 



THE LAMP CANNOT BE STARTED 



61. This may be because there is no voltage in the main line. 

 The presence of current is easily determined by using the testing 

 incandescent lamp (fig. 21). An incandescent lamp in the circuit 

 as shown in fig. 2 or 4 will show whether the current extends to the 

 lamp switch. 



FIG. 21. TESTING INCANDESCENT LAMP. 



W l W? The two supply wires for the lamp. 



For this testing lamp a socket without key switch is best. It is also wise to 

 have the lamp protected by a wire guard. The wires at W-, W 2 should be 

 exposed only a short distance as shown. 



To test with the lamp put the naked ends of the wires W t W., upon metallic 

 parts of the circuit to lie tested being sure to make contact with both conduc- 

 tors of the circuit. For example, the two wires or the two blades of a knife 

 switch, etc. If there is voltage in the line at that point the lamp will light up. 



62. The connections in the arc lamp may not be good, that is, 

 the set screws holding the connecting wires may have become 



