ALTERNATING MOTORS FOR RAILWAY WORK. 183 
Most street railway men strongly dislike the dou- 
ble trolley in any form, and beyond question it compli- 
cates the overhead work, where crossings and turnouts 
are frequent, in the most frightful manner. Nevertheless 
even for city work it can be made steadily operative, 
as the experience of some years in Cincinnati has shown. 
The principal advantages of the continuous current, double 
trolley system which are its only excuse for existence,viz., 
the independence of track condition as regards motive 
power, lessened interference with other circuits, and ab- 
sense of electrolysis, do not apply with the same force to 
a double trolley polyphase system. Omne branch of the 
circuit is still grounded and bad track contact is bound to 
be felt in the operation of the motors under some con- 
ditions. In short the double trolley for polyphase work is a 
disagreeable necessity and nothing better. 
Again, however, comes to the rescue the fortunate 
circumstance that in much of the long distance work for 
which alternating motors are desirable a double trolley wire 
is less objectionable than elsewhere. 
The matter of lagging current is more serious. Were 
all induction motors possessed of as good power factors as 
the one shown in Fig. 97 there would be no trouble, for the 
lagging current is too small to influence much either the 
capacity of the plant or its regulation. But armature 
clearance is a potent factor in varying the power factor, and 
the motor in question being intended for hoisting had a 
clearance but little over /% in. This is too small for the 
rough and tumble work of electric railroading, and with 
double this clearance, as in case of the motors of Fig. g9, the 
power factor is not nearly so favorable. A good power 
factor of .85 to .go is very hard to obtain in motors of 
moderate size and speed such as would be used in street 
railway practicz, and a poor power factor means mischief. 
Take for example a power factor of .75. This means 
that a third more current must be generated and distrib- 
uted than is indicated by the emergy and the voltage of 
supply. Hence the saving in copper effected by the three