ALTERNATING MOTORS FOR RAILWAY WORK. 175 
motor is up to speed these are short circuited by a solid 
ring slipped a couple of inches along the shaft by the small 
handle shown alongside the bearing. Sometimes this re- 
sistance is in two or more sections, successively short cir- 
cuited by a similar motion of the ring. This arrange- 
ment does away once for all with all moving contacts. The 
  
FIG. 5. 
field, being stationary, can be safely wound for higher 
voltages than if it were rotating and suffers less mechani- 
calstrain at all voltages. ‘T'he machine thus requires very 
little attention, and besides is quite free from all danger of 
sparking, sometimes a very undesirable possibility. 
Both the constructions shown have merits for special 
purposes. The revolving armature arrangement gives a 
simpler and safer machine for most ordinary purposes, and 
especially for high voltage work without transformers. 
The revolving field is the better for very large motors and