174 



Introduction to the Study of Science 



for heating, cooking, and power. A poorly constructed lamp, 

 flat iron, oven, or motor consumes more current than necessary 

 in doing the required work. For this reason it is economy to 

 employ only the best made and most efficient appliances. 



KILOWATT-HOURS 



FIG. 49. Kilowatt-hour electrical meter. Each division of the right hand 

 dial indicates one kilowatt hour. 



69. The arc light. The mechanism controlling the carbons 

 of the arc light, whether in the old style or in the later forms, 

 such as the flaming arc, can be understood more readily by 

 direct observation than from description. The " hand-con- 

 trolled " feed as used often 

 in the arc light for a stere- 

 opticon (Fig. 50) is perhaps 

 most instructive in getting 

 the fundamental principles. 

 In the automatic arc lamp 

 several kinds of mechanism 

 are employed, one or more 

 of which you may find avail- 

 able for study. These are 

 the gravity feed, clockwork, 

 ,, clutch, hot wire, and motor 



FIG. 50. Arc lamp, controlled by hand. ' 



feed. A magazine arc lamp, 



one with six or more pairs of carbons, which are supplied as 

 required to give a long, continuous flame, is interesting, and 

 may be made the subject of a report by a member of the class. 



