492 



FARM MOTORS 



Since the carbons of the arc lights are constantly wast- 

 ing away there must be some device to regulate the dis- 

 tance they are from each other and to work automatically 

 to keep them at this distance. An ingenious appliance 

 of electromagnets and clutches accomplishes this action 

 and is explained in any book upon electric lighting. 



662. Incandescent lamps. It is on the principle of the 



heated wire that we get light from the in- 

 candescent lamp. Referring to Fig. 370, 

 connections are made with the lamp at A 

 and B. At CC are bits of platinum wires 

 attached to the carbonized filament D. E 

 is the highly exhausted globe. If the car- 

 bonized filament were in the air, the intense 

 heat created within it due to the resistance 

 of the current would immediately burn it 

 up, but since it is in almost perfect vacuum, 

 it will last from 600 to 800 hours. Even at 

 the end of this period the filament does not 

 always break, but it becomes so disinte- 

 grated that the candle power is low and 

 further use is not satisfactory. 



663. Commercial rating of incandescent lamps. 

 Before a lamp is put upon the market it is compared 

 with a lamp of known brilliancy. While it is being com- 

 pared with the standard lamp, measurements of its 

 voltage and current are made. After this is done the 

 lamp is labeled with the voltage it carries, its candle 

 power and watts consumption. A 16 C.P. 6o-watt no- 

 volt lamp will require 



W 160 

 C = = = . 55+ amperes. 



Lamps are usually made for circuits of 50 to 60 volts, 

 I jo to 115 volts and 220 volts with constant potential. 



FIG. 370 INCAN- 

 DESCENT LAMP 



