59 



alternator was connected with a bank of 

 transformers, and the secondaries of the 

 latter with lamps and other resistances. 

 A Siemens dynamometer was inserted 

 into the armature circuit, and the second- 

 ary currents from the transformers were 

 occasionally measured by a Sir William 

 Thomson's ampere balance. The primary 

 and secondary currents were found to be 

 very nearly in the ratio of 1 to 20. The 

 exciting current was adjusted by a rheo- 

 stat, and measured by a spring-solenoid 

 instrument. The first run was made with- 

 out external current in the armature cir- 

 cuit, except the small amount necessary to 

 record the pressure by the stepdown 

 transformer. In this manner, data were 

 obtained for plotting the static charac- 

 teristic OS. In the diagram the excit- 

 ing power is plotted on the horizontal 

 and the pressure on the vertical. The 

 exciting power was found by multiplying 

 the exciting current by 280, there being 

 one hundred and forty turns of. wire on 

 each magnet-coil. The resistance of the 

 armature when warm is 1.74, and that of 



