I72 POWER DISTRIBUTION FOR ELECTRIC RAILROADS. 
the windings which deliver current to the armature are used 
alternately for this purpose and for establishing a field 
with which the induced current can react, or whether in- 
ducing and field windings are specialized; whether the 
structure is so disposed that there is a true resultant rotary 
magnetization or whether there exists a rotary pole only in 
the sense in which the poles rotate in a continuous current 
armature—all these are questions which have but a trivial 
bearing on the actual properties of the machines. As a 
matter of fact induction motors are much closer in prin- 
ciples and properties to continuous current:motors than is 
generally supposed. Like shunt motors they tend to run 
at a constant speed and when the load changes they speed up 
or slow down just enough to permit enough armature cur- 
rent to flow to adjust the motor to.the new conditions of 
load. Like shunt motors too, they require at starting a re- 
sistance in the armature circuit to keep the starting cur- 
rent within bounds.