CH. X] 



DRAWING WITH HOUSE CURRENT 



339 



PROJECTION DRAWING APPARATUS WITH THE RADIANT 

 CONNECTED WITH THE HOUSE LIGHTING SYSTEM. 



486. General Statement. As shown in Chapter III (fig. 

 41-43), the arc lamps using small, cored carbons (6 to 8 mm. in 

 diameter) and drawing from three to six amperes may be connected 

 with any socket for an incandescent bulb of the house lighting 

 system. The light so obtained is more powerful than the usual 

 lime light. The carbons being small, the light approaches closely 

 to the ideal point source. Consequently for all projection pur- 

 poses, including drawing, this form of arc light is of the greatest 

 importance and utility. Of course, for projection in a large hall 

 it is insufficient, but for the relatively small screen pictures needed 

 in drawing and for small classes, the results are very satisfactory. 



487. Wiring, rheostat and connections for the arc lamp 

 attached to the house lighting system. This is shown in fig. 188- 

 189 and described in 128-135. Remember and practice the 

 advice given about turning the current on and off ( 133), and the 

 possibility of short circuiting and burning out the incandescent 

 bulb socket. Never use an arc lamp without a suitable rheostat 

 or inductor. (See 129, also i28a for fuses on the house system). 



FIG. 1 88. WIRING AND CONNECTIONS OF THE ARC LAMP USED ON THE 

 HOUSE LIGHTING SYSTEM (See fig. 45). 



