DIRECT FEEDING SYSTEMS. 65 
Occasionally, too, on single track roads with frequent 
turnouts, two trolley wires are strung ten or twelve inches 
apart, each to accommodate the cars running in one direc- 
tion, so as to entirely avoid overhead switches of any kind. 
This arrangement is shown in Fig. 44, and while it is not 
now very widely used, it is exceedingly convenient in cer- 
tain cases. In Fig. 44 the track at a turnoutis shown by 
the solid lines and the two trolley wires by dotted lines. 
The trolley wire, A B, would naturally be used by cars run- 
ning from right to left asindicated by thearrow, while C D 
would be used by cars running from left to right. Each 
car keeps to its own trolley wire throughout the track, un- 
less it is mecessary to change over in backing around a 
turnout. ‘T'his double trolley device enables long exten- 
sions to be handled without feeders. 
  
  
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o e, S 
    
Street Ry. Journal 
FIe. 44. 
Before passing to the actual computation of a trolley 
and feeder system, we must go back to our two funda- 
mental propositions and inquire into the permissible maxi- 
mum drop and what we mean by average drop. 
Suppose that ten per cent average drop has been de- 
cided upon in a given case,—What is really meant by this? 
There has been considerable confusion on this point. Are 
we to understand that this average drop is that determined 
from the effect of the maximum working load throughout 
the system, or is it the average loss on the parts of the sys- 
tem considered separately irrespective of their relative 
amounts. Is it the drop produced by the average load or 
the average of the drops produced by the simultaneous 
loads at some particular time? 
T'o reduce the matter to a common basis with other 
cases of the electrical transmission of energy, weare at lib-