CH. XI] MAGIC LANTERN AND MOVING PICTURES 



415 



The carbons may be at right angles (fig. 23 C). 



The carbons may be inclined backwards about 30 (fig. 230 a). 



The upper carbon may be inclined backward 45, the lower 

 carbon being vertical (fig. 230 c). 



The carbons may come together in the form of a horizontal V 

 with the point towards the condenser (fig. 23 D). 



Both carbons may be vertical (fig. 230 b). 



Whatever carbon setting is used, the arc must be held, so that the 

 crater or craters face the condenser. 



The form of the arc can be watched by observing it through the 

 smoky glass window or by the pinhole or lens image on the wall 

 ( 567). When using alternating current the sound will give an 

 indication as to whether the arc is of the right length. 



Constant vigilance in watching the arc is one of the requirements 

 for success is showing moving pictures. During an exhibition, 

 never let the arc go out. 



581. Supply of carbons for the arc lamp. A good supply of 

 carbons should be provided and placed where they may easily be 

 reached. The carbons are soft-cored and their size should be 

 suited to the current used (see 753a). Generally 16 mm. carbons 

 (^ in.) are used, both being of the same size. 



582. Position of the film in the machine. When a film is 

 passing through the machine the rule for its position is the same 

 as with the lantern slides, that is, the picture should appear correct 

 when one looks through it toward the 

 screen but it must be upside down. 

 To accomplish this one should bear in 

 mind that as the films are printed they 

 will appear correct when one looks at 

 the emulsion side just as with a lan- 

 tern slide or an ordinary paper print. 

 Therefore, the light is made to strike 

 the emulsion side of the film. 



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583. Mechanism. Without go- 

 ing into the details of the special 



FIG. 230. POSITION OF CAR- 

 BONS FOR MOVING PIC- 

 TURE PROJECTION. 



a Inclined. 

 b Vertical. 



c Upper carbon inclined, 

 lower carbon vertical. 



