DIRECT FEEDING SYSTEMS. 69 
value of the load on an electric railway is so uncertain, 
whether for any stated time or during any interval, and so 
uncertain in position as well as amount, that the success of 
any calculation depends almost wholly on the skill with 
which the data are assumed. _ 
A convenient way of entering upon the calculation of 
a conducting system is to take up the data involved in the 
following consecutive steps. 
1. Extent of lines. 
2. Average load on each line. 
Center of distribution. 
Maximum loads. 
Trolley wire and track return. 
General feeding system. 
7. Reinforcement at special points. 
The first two steps are necessary preliminaries to the 
third. ‘The fourth determines the permissible drop, the 
fifth gives the division of the overhead copper between 
trolley and feeders, and the allowance that must be made 
for the resistance of the return circuit. The sixth stage is 
the preliminary calculation of the conductors and the 
seventh the modification of this to take full account of local 
conditions. ‘The application of the whole process is best 
shown by working out an hypothetical system in detail, 
step by step. ‘Two cases may properly be taken up; first 
a regular street railway system, and second, an interurban 
line of moderate length. 
Suppose a new system is to be installed or an old one 
reorganized of which the track is shown in the simple chart 
(Fig. 46). Here the main line, A B CD, is double track 
throughout. A B is 10,000 ft., B C 2000 and C D 4000, 
making a total length of 16,000 ft. At B C the main line 
is joined by the single track branch, C E, 10,000 ft. long, 
on which at F G is a five per cent grade 2000 ft. long. 
Step 1. Lay out the track to scale, noting the dif- 
ferent distances carefully and the extent and position of 
grades. 'The scale need not be large, say, an inch to the 
thousand feet, and a couple of tracings of the chart will 
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