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. 
W, Wi 
Fig. 283. Water Cooled Rheostat. 
H'„ W3 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, ]Vt. The rheostat is then immersed in 
running water and the containing vessel of wood, glass or stoneware is placed in 
a sink.