made special observations upon the work required to move the car
between the 20th September and 15th October, 1885. Seals were attached to
the accumulators. Moreover, from the 27th of September, after each
charge, seals were placed on the belts from the steam-engine to prevent
any movement of the Gramme machine, so that there could be no charges put
into the accumulators beyond those measured by the jury.

The instruments used for measuring were Ayrton's amperemeter and Deprez's
voltmeter, which had been tested in the exhibition by the Commission for
Experiments on Electrical Instruments, under the presidency of Professor
Rousseau. Besides this, Siemens' electro-dynamometer and Ayrton's
voltmeter were used to check the results; but there was no practical
difference discovered. During the period of charging the accumulators,
the intensity of the current and the electromotive force was measured
every quarter of an hour, and thence the energy stored up in the battery
was deduced. It may be mentioned that the charge in the accumulators,
when the experiments were commenced, was equal in amount to that at their
termination.

An experiment was made on 21st October to ascertain, as a practical
question, what was the work absorbed by the Gramme machine in charging
the accumulators. The work transmitted from the steam-engine was measured
every quarter of an hour by a Siemens dynamometer; at the same time the
intensity of the electromotive force given out by the machine, as well as
the number of the revolutions it was making, was noted. It resulted that
for a mean development of 4 mechanical horse power, the dynamometer gave
into the accumulators to be stored up 2.28 electrical horse power, or 57
per cent. The intensity varied between 25.03 and 23.51 amperes during the
whole time of charging. Of this amount stored up in the accumulators a
further loss took place in working the motor; so that from 30 to 40 per
cent. of the work originally given out by the steam-engine must be taken
as the utmost useful effect on the rail.

It was estimated that to draw the carriage on the level 0.714 horse power
was required, or if a second carriage was attached, 0.848 horse power
would draw the two together. This would mean that, say, 2 horse power on
the fixed engine would be employed to create the electricity for
producing the energy required to draw the carriage on the level.

The electric tram-car was quite equal in speed to those driven by