CH. XIII] 



RHEOSTATS AND OTHER BALLAST 



527 



If one wishes a greater amperage the upper wire is lowered in the 

 barrel and if less current is desired the upper iron is lifted higher 

 in the barrel (fig. 282). Of course there must be some means of 

 holding the upper wire in position when it is at the right height 

 in the barrel. 



Wi 



Wi 



FIG. 283. WATER COOLED RHEOSTAT. 



W t , W 2 Conductors. 



R Rheostat composed of the proper length of small naked wire wound 

 around a frame of wood. The two ends of this resistance wire are soldered to 

 the cut ends of the supply wire W 3 W a . The rheostat is then immersed in 

 running water and the containing vessel of wood, glass or stoneware is placed in 

 a sink. 



