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 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.