The second, more formidable, objection relates to the weight of
storage batteries--and this involves two disadvantages, viz., waste of
power in propelling the accumulator along with the car, and increased
pressure upon the street rails, which are only fitted to carry a
maximum of 5 tons distributed over 4 points, so that each wheel of an
ordinary car produces a pressure of 1¼ tons upon a point of the rail
immediately under it.

The last mentioned objection is easily overcome by distributing the
weight of the car with its electrical apparatus over 8 wheels or 2
small trucks, whereby the pressure per unit of section on the rails is
reduced to a minimum. With regard to the weight of the storage
batteries, relatively to the amount of energy the same are capable of
holding and transmitting, I beg to offer a few practical figures.
Theoretically, the energy manifested in the separation of one pound of
lead from its oxide is equivalent to 360,000 foot pounds, but these
chemical equivalents, though interesting in themselves, gives us no
tangible idea of the actual capacity of a battery.

Repeated experiments have shown me that the capacity of a secondary
battery cell varies with the rate at which it is charged and
discharged. For instance, a cell such as we use on street cars gave a
useful capacity of 137.3 ampere hours when discharged at the average
rate of 45.76 amperes, and this same cell yielded 156.38 ampere hours
when worked at the rate of 22.34 amperes. At the commencement of the
discharge the E.M.F of the battery was 2.1 volts, and this was allowed
to drop to 1.87 volts when the experiment was concluded. The entire
active material contained in the plates of one cell weighed 11.5 lb.,
therefore the energy given off per pound of active substance at the