INTERURBAN AND CROSS COUNTRY WORK. 209 
ing in a plant of this size, with, perhaps, the weight of ad- 
vantage rather in favor of the former alternative. At this 
output, however, one is quite near the point at which the 
construction of direct coupled machines becomes embarrass- 
ing on account of low speed, and it often happens that the 
belted plant is not only cheaper, but more efficient. It 
most emphatically does not pay to couple directly to a sim- 
ple, non-condensing engine, instead of belting to a Corliss 
type engine in a plant of this size. It always pays to con- 
dense, and it nearly always pays to use compound engines. 
The simple, single valve, non-condensing engine is an eco- 
nomic abomination in such a plant, and should not be con- 
sidered for a moment. ‘The author’s choice would be a 
compound condensing engine, with independent admission 
and exhaust valves, running not less than 120 to 150 
r. p. m. Such an engine plant will produce power at 
about two-thirds the cost by ordinary simiple engines, and 
very nearly as cheaply as the best that can be done under 
similar circumstances by the best triple expansion engines 
which, in a plant of the size considered, are less suited to 
the conditions of variable load than compound engines. 
We may now take up the distribution step by step. 
For a constant we may safely take 14, as representing the 
case of a good track and moderately heavy traffic. 
Beginning with the section E A, we may safely assume 
that about one-fourth the total load will be concentrated 
upon it, and uniformly distributed. We will assume a 
No. ooo trolley wire of 167,000 c. m., weighing 2677 1bs. 
per mile. This wire will carry 100 amperes, the maximum 
current for a single car, over 4000 ft., with moderate loss 
of voltage. 'Three cars normally belong on the section, 
and we must meet the contingency of all three being at A 
and loaded, calling for, say, 200 amperes. In this con- 
tingency we should be justified in assuming as much as 
100 volts drop in the feeders alone, and that not more 
than one other car will be fairly upon the section. At five 
miles distance the delivery of 200 amperes under these 
conditions calls for 728,000 c. m. 'This may be very ad-