158 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1907. 
irregular track, than its rival, a larger portion of whose weight heels 
over and increases the vertical pressure on the rail. Careful investi- 
gation, however, carried on through many sources, seems to indicate 
that with electric motors properly guided any increased tendency to 
side thrust is more than compensated for by certain other advan- 
tages. : 
Train control and operation.—Restriction of operation in an elec- 
tric system to methods in vogue with steam operation would be a 
useless throwing away of one of the greatest possibilities of improve- 
ment in train operation where passenger service is heavy and terminal 
facilities congested. Ten years ago I inaugurated on the South Side 
Elevated of Chicago a new system of train control, which permitted 
the aggregation into trains of any number of independently equipped 
motor cars, and dead cars if desired, and their control from either 
end of any car, irrespective of train make-up. This system, now 
known the world over as the “ multiple-unit ” (fig. 6), has made 
such advance that it is now generally recognized and adopted as the 
best method of handling trains wherever service is crowded and high 
schedules are required. 
The essential result accomplished by this system is increase of 
capacity, by providing high power equipments, proportional to the 
length of the train, increased schedules and density of train move- 
ment, the lowest maximum speeds for any given schedule similarity 
of equipment, reduced switching and signal movements, increased 
safety, and generally the utmost independence and facility of opera- 
tion. Whatever tentative plans may for the present be adopted, I 
believe that it is inevitable that all local and suburban passenger 
service on electrically equipped railways requiring train operation 
will be eventually conducted on the multiple-unit plan, and its use 
will spread over a continually increasing area, even to the operation 
of passenger cars run over divisions of considerable length. 
Storage batteries —The use of the storage battery in connection 
with electric railway operation is a proposal concerning which much 
may be said, for and against, depending largely upon what value one 
attaches to restriction of peak loads on moving machinery and to in- 
surance. That it has been and is being used successfully in connec- 
tion with direct-current equipment of moderate potential admits of 
no dispute, and it has been stated that it is equally available for 
alternating-current installations. This latter claim is misleading. 
On direct-current systems the principal function of a battery is 
that of an equalizer. If installed at a central or substation it is 
usual to provide boosters to govern the charging and discharging. 
These, however, are only of differential watt capacity, and while they 
are necessary for regulation, it is perfectly possible to use the battery 
in some emergencies by direct connection with the line. 
u 
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