FUNDAMENTAIL PRINCIPLES. 19 
a center of supply at or near the center of gravity of the load 
is the cost of site. For a regularly constituted generating 
station this cost is often prohibitive, so that it is far cheaper 
to endure the great increase of copper necessary for feed- 
ing from a distance. If the central plant be reduced to a 
substation for supplying an alternating current to the 
working conductors, the space taken up is so trivial that 
its cost is almost nominal. ‘The reducing transformers 
for a capacity of 1000 k. w., together with switch- 
board and all necessary station apparatus can easily be 
  
  
  
BIG. T12; 
accommodated in a room ten feet square, if compactness is 
necessary. Nor is there any need of extreme care in the 
matter of foundations, since there is no moving machinery, 
save motors for ventilation, in such a substation. 
Even if the day of ai.ernating motors for railway service 
be delayed far longer than now seems probable, there are 
not a few cases in which substations with motor-generators 
are preferable in point of economy to an immense invest- 
ment in feeders. At present prices of apparatus such a 
condition will be met far oftener than would at first glance 
seem probable. In large cities, where there is & strong 
and growing tendency to force all feed wires underground,