Van Name — A Rheostat for Large Currents. 351 



wooden cross-pieces M, was always placed over a sink when in 

 use. 



The device for turning the resistor and holding it in any 

 desired position was attached to the portion of the axle which 

 projected outside the box. It consisted of a radial arm JY, 

 carrying a spring catch P which engaged in a series of holes 

 arranged in a circle in a brass plate Q attached to the outside 

 of the box. No stress is laid upon the construction of this 



Fig. 2. 



part of the apparatus, since it is immaterial what device is 

 used for the purpose, so long as it permits quick adjustment 

 and holds securely. Since the lug C turned with the axle, a 

 flexible cable was needed for the current connection at this 

 point. 



The resistance of the rheostat, when fitted with the resistor 

 generally employed, covered the range from 0*22 ohm down 

 to 0*015 ohm, measured between terminals. This resistor was 

 shaped almost exactly as shown in figure 1, the narrow portion 

 having a cross-section of about \ by \ inch for the greater part 

 of its length. So far as was observed, prolonged use produced 

 no deterioration or change in this graphite resistor, but it was 

 finally broken by accident. Another resistor of the same 

 dimensions was subjected as a test to a load of over 4000 watts 

 (170 amperes X 24 volts) for thirty minutes without the slight- 

 est injury, and could, apparently, have safely carried a consider- 

 ably heavier load. 



