FAST AND HEAVY RAILWAY SERVICE. 267
thing as yet proposed for heavy currents. With very high
voltage the overhead or side running trolley becomes nec-
essary. At ordinary voltages the feeder section required at
even moderate distances is formidable. To operate two
locomotives of the Baltimore & Ohio pattern on a two mile
section with the power house at one terminus requires a
capacity for delivering the equivalent of about 3000 amperes
at the end of the line. From Plate II, using 16 as track con-
stant, since the conductivity of the track cannot safely be
taken as more than twice that of the outgoing system, the
feceder area required for a transmission of 10,000 ff. .at
100 volts loss is 4,800,000 c¢. m. Using 100 1b. center rails
on a double track one gets about 2,200,000 c. mi. equiv-
alent conductivity, leaving 2,600,000 to be supplied by
supplementary feeders. By allowing a little extra drop
this could safely be reduced to, say, two 1,000,000 C. m.
cables.
It at once becomes evident that direct supply at ordi-
nary voltages is out of the question, except for relatively
very short distances. For more extensive work we are
brought back either to high voltage supply with trans-
formers on the locomotive or with a low voltage working
conductor supplied from transformers along the track.
Direct current working is practically barred out by the con-
ditions of practical working, although current reorganizers
on the car have several times been suggested.
The cost, weight, and loss of efficiency in such appar-
atus, however, render it so cumbersome that it can be con-
sidered only as a last resort. 'The present state of alternat-
ing motor practice renders it improbable that we shall ever
be driven to that resort.
For heavy special service in yards and tunnels the cen-
ter rail is undoubtedly the simplest and most practical
method of distribution yet tried, and for such service con-
tinuous current motors at 600 to 1000 volts with series-paral-
lel control, leave little to be desired. If in the course of
development alternating long distance service has to be
linked to heavy terminal traffic, a terminal power system at
