188 POWER DISTRIBUTION FOR ELECTRIC RAILROADS. 
be immediately available for railway purposes, although 
they have come abroad into considerable use for general 
motor work in connection with lighting service. 
They may be divided into two classes, rather distinct 
from each other in method of operation, although closely 
similar to each other in principle and in practical qualities. 
First may be mentioned those motors which are oper- 
ated as true polyphase motors by derived polyphase cur- 
rents obtained by splitting up a monophase current. In 
this case the actual motor is a true polyphase machine with 
all the properties thereto belonging, and the real novelty 
of the system lies in the special methods of transformation 
  
FIG. T03. 
adopted in breaking up an ordinary alternating current 
into symmetrical components. 
Systems of this sort have been brought forward in this 
country by C. S. Bradley and abroad by M. Désiré Korda. 
They are somewhat complicated, but are nevertheless 
operative, and may find a field even in electric traction, 
particularly in special problems in railroading. 
The apparatus of Mr. Bradley is shown in diagram in 
Fig. 104. The process employed consists essentially of 
two operations—the splitting up of the original current 
into two components, differing in phase by go degs., and, 
second, the combination of these to obtain a three phase 
resultant system. In the diagram, A is the generator, 
B one section of the transformer primary system, D a 
condenser which acts in conjunction with the inductance