136 POWER DISTRIBUTION FOR ELECTRIC RAILROADS. 
and the power of such a pressure to break down insulation 
is most formidable. If in addition to sc great an electric 
strain the armature insulation has to stand prolonged 
vibration and centr#fugal strain its life is likely to be some- 
what uncertain. For these high voltages therefore a ma- 
chine with a stationary armature is much to be preferred 
to the ordinary types, especially since the latter have no 
compensating advantages. 
  
Another and a very ingenious form of generator with 
two phase stationary armature is shown in Fig. 77. Here 
the armature is composed of two laminated rings placed 
side by side in a common frame a short distance apart. 
Fach is slotted to receive heavily insulated rectangular 
coils as shown in Fig. 78. The revolving part of this 
machine, is simply a steel casting furnished with a set 
of outwardly projecting laminated pole pieces at each 
end. The field winding is a single fixed circular coil 
around the field between the two armature rings. The 
armature current is taken off from fixed binding posts 
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