94 POWER DISTRIBUTION FOR ELECTRIC RAILROADS. 
motor, or when one motor slips or develops faults that 
might cause trouble were the motors simply in series. 
The track need not be heavily bonded with this construc- 
tion since it has to carry only occasional and moderate cur- 
rents. ‘The saving in copper is the same as that already 
indicated for the regular three-wire system, with the ad- 
ditional advantage that the track connections are easily 
made and do not require so great and constant care as is 
the case when a full track return is used. 
The employment of two trolleys would be considered 
a first class nuisance by most electric railway managers, 
but for heavy work when large currents, say a couple of 
Dl ¥ 
F 
BrG a5l 
hundred amperes, are to be dealt with, there is something 
to be said in favor of trolley contacts in duplicate. These 
granted, they can be made on two trolley wires without 
much extra trouble. 
This self contained. three-wire system seems well 
adapted for heavy interurban service, particularly in con- 
junction with local service at the termini. As the motors 
are comparatively independent of ground connections the 
track could be more easily kept in operative condition 
through the winter. The system lends itself very readily 
to cases like Fig. 50, in which the interurban cars could 
well be connected in the manner described and the local 
cars in the ordinary fashion of three-wire roads. 
None of the methods so far described are able to effect 
a really satisfactory saving in copper, without involving 
special arrangements that are somewhat serious in general 
practice. Boosters, using the word in its ordinary sense, 
waste energy in a very objectionable manner, increasing