FUNDAMENTAIL PRINCIPLES. 28 
it may be convenient to take A D CB asa single conductor 
carrying a load 7, +7;+75, and AETF B asanother loaded 
with Z,+7,+7,. DEFE and D F may then be taken sepa- 
rately. 
Now, this skeleton must be padded with reference to 
the second condition mentioned. Suppose that trafficis 
liable to be congested at or near B. This point is fed by 
the two main lines in multiple. If the drop chosen for 
these in making the skeleton would mean a drop at B 
sufficient to seriously impede traffic, enough copper must 
be added to relieve this condition. Just where this addi- 
tion should be made requires the exercise of considerable 
discretion. If F is a point where congestion is also to be 
feared the line, ADF, should be strengthened, being the 
nearest route. If C be threatened, A D C should be rein- 
forced. In efther case the addition should be sufficient to 
put B out of danger. In any case z; and 74 should be con- 
sidered with reference to the lines, A D and A E, and the 
drops in DE and D F so taken as to keep them at good 
working pressure in spite of any excessive demands near 
the terminus of the system. In other words, for railway 
work it is nearly always possible to split up a network 
into a combination of linear systems and branches, since 
the loads are, or may be, so uncertain that fine discrimina- 
tion in minor lines is out of the question. 
A good development of this splitting principle may be 
found in Fig. 15, which is a network of three meshes com- 
posed of two parallel lines, A and B, cross tied by the lines, 
CD,EF,GH,IJ. Let Abe a feeder and B the trolley 
wire and we have the well known ‘‘ladder’” system of 
feeding in. As, in practice, CD, EF, etc., are very short 
compared with CE, E G, etc., the system may be regarded 
as composed of A and B in parallel, the only qualification 
being due consideration of the possible drop in B between 
a load point and the two nearest feeding points. But we 
may suppose A and B to run in adjacent streetsand the 
former to be connected to another trolley wire on its own 
street, then a track to run along GH, and so on until