So MAGIC LANTERN WITH SMALL CURRENTS [Cn. Ill 



124. Room for projection. Any room may be used at night, 

 and this makes these magic lanterns especially adapted for the 

 home. 



In the daytime, of course, the room where they are used must 

 have shutters or curtains so that it can be darkened. 



125. Screen for the image. The screen need not be over 

 three or four meters square (9-1 2 feet) . For many purposes a large 

 sheet of cardboard, 72x120 cm. (28x44 in-) makes the best 

 possible screen (see Ch. XII). 



For home use a white wall or a well stretched sheet will serve. 

 If the screen is to be used frequently in the same place in the 

 laboratory or home it is desirable to use a white wall or a regularly 

 painted screen (see 621-630). 



126. The magic lantern and its support. Any of the good 

 modern forms of magic lantern can be used. Special small and 

 compact lanterns have been constructed for this purpose, and they 

 are excellent and cheap (see prices in the appendix) (fig. 51-52). 



For a lantern support any table of sufficient height may be used. 

 A pile of books or an empty box on an ordinary table will serve 

 to raise the lantern sufficiently. 



ARC LAMPS FOR THE HOUSE CIRCUIT 



127. Small arc lamps, using small carbons only, are con- 

 venient ; but the ordinary large arc lamp can be used if the screws 

 for clamping the carbons are long enough, or by means of bushings 

 or adapters for the small carbons (for wiring and rheostat, see 

 128-129). 



The small carbon arc lamps are easily managed, and the amount 

 of light they give (see 756) much more than offsets the attention 

 they require over the other lamps used on the house circuit. 



If a lamp must be purchased for use on the house circuit, one of 

 small size is preferable. They arc designed for the small carbons 

 only. They arc nearly always of the hand-feed type, but when 

 direct current is available there arc automatic lamps to be had. 

 The Thompson automatic arc lamp, and the Bausch & Lomb 



