above high rate of discharge was 62.225 foot pounds, and when
discharging at the lower rate of 22.34 amperes the available useful
energy was 72.313 foot pounds, or nearly 2.2 electrical horse power
per pound of active matter. But this active substance has to be
supported, and the strength or weight of the support has to be made
sufficiently great to give the plate a definite strength and
durability. The support of the plates inclusive of the terminals above
referred to weighs more than the active material, which consists of
peroxide of lead and spongy lead; so that the plates of one cell weigh
actually 26.5 pounds. Add to this the weight of the receptacle and
acid, and you get a total of about 41 pounds per cell when in working
order. Seventy of these cells will propel an ordinary street car for
four hours and a half, while consuming the stored energy at the rate
of 30 amperes, or over 5.6 electrical horse power. The whole set of
seventy cells weighs 2,870 lb., which is barely one-fifth of the
entire weight of the car when it carries forty adult passengers.
Therefore the energy wasted in propelling the accumulator along with a
ear does not amount to more than 20 per cent. of the total power, and
this we can easily afford to lose so long as animal power is our only
competitor. From numerous and exhaustive tests with accumulators on
cars in this country and abroad, I have come to the conclusion that
the motive power for hauling a full-sized street car for fifteen hours
a day does not exceed $1.75, and this includes fuel, water, oil,
attendance, and repairs to engine, boiler, and dynamo. We have thus an
immense margin left between the cost of electric traction and horse
traction, and the last objection, that relating to the depreciation of
the battery plates, can be most liberally met, and yet leave ample
profits over the old method of propulsion by means of animals.

The advantages of storage battery street cars for city traffic are