174 POWER DISTRIBUTION FOR ELECTRIC RAILROADS. 
construction has several well marked advantages. 'The 
primary element in which the heaviest hysteretic loss occurs 
is reduced to the smallest practicable dimensions. The 
secondary being stationary can have resistance put in series 
with it through ordinary binding posts, sometimes a great 
convenience, and since the secondary winding is, as shown, 
very simple, the armature can be splitlike the field of a 
  
FIG. 94. 
dynamo and the upper half lifted off to permit inspection 
cr removal of the revolving field. As the clearance in in- 
duction motors is usually very small, 14 in. or less, such an 
arrangement is very convenient. 
Fig. 95 shows a fine three phase motor of 125 1 D il 
which the armature revolves while the field is stationary. 
The main leads are taken to the connection board on the 
top of the motor, and there are no moving contacts what- 
ever. The resistance used in starting the motor is stowed 
inside the armature ring and its terminals brought out to 
three contacts secured to the armature spider. - When the