118 POWER DISTRIBUTION FOR ELECTRIC RAILROADS. 
important. ‘The choice of compound instead of triple ex- 
pansion engines was probably a wise one, since while the 
latter are a trifle more economical at full load, they are less 
able to cope efficiently with great variations of load, such 
as met in railway work. Only in the largest stations can 
they be so worked as to take full advantage of their low 
steam consumption. ‘T‘'he engines are separable, so that in 
an emergency either the high or low pressure cylinder can 
be worked as a simple engine. 
The boilers are Babcock & Wilcox designed to supply 
steam at pressures as high as 180 lbs. and are set in three 
banks of 500 nominal horse power each. 
The arrangement of the station, as a glance at Fig. 
67 will show, is exceptionally good. The whole plant 
is very compact, the piping between boilers and engines is 
very short, and, what is rather unusual, the switchboard is 
where it ought to be, close to the other apparatus, on the 
same level and perfectly accessible. The accessories are very 
complete and the whole plant is a fine example of the most 
advanced modern practice. Almost the only question that 
could be raised concerning it would be the desirability of 
using vertical marine type engines, which are of equally 
high efficiency, slightly higher speed and take up much 
less floor space. For auxiliary-station work with a greater 
number of power units or for use in a principal station there 
is much to be said in their favor, but in the case in hand, 
where ground space is not relatively very valuable, and 
only two great units were to be installed, honors are pretty 
even, with this advantage on the side of the horizontal 
engine that the cylinders can be worked independently 
with far greater ease than in the case of a vertical en- 
gine. 
It is altogether probable that power can be generated 
in this station quite as cheaply asin the main Albany Street 
station, as the latter is not yet completely remodeled and 
brought up to date. In any event a cursory comparison 
with our curves of cost shows that the output of the 
Charlestown station is great enough to bring it to a very