the time of charging the reservoirs
on the motor, was 63.8 atmospheres, at a temperature of 68 deg. F. One
atmosphere was lost by letting the air into the pipe laid between the
shed and the tramway where the motor stood; when the reservoir on the
motor was charged, the pressure fell to 42.6 atmospheres in the fixed
reservoirs, at a temperature of 55 deg. F.

The pressure in the reservoir on the motor, when ready to start, was 42.6
atmospheres, at a temperature of 84 deg. F. On its return, at the end of
forty-six minutes, after a journey as above mentioned of about three and
a quarter miles including the triangle, the pressure had fallen to 20.9
atmospheres, and the temperature to 71 deg. F. The weight of air used during
the journey was thus about 110 lb., or, say, 34 lb. per mile. The coal
consumed by the stationary engine to compress the air amounted to 39 lb.
per mile, in addition to 3 lb. of coke per mile for warming the exhaust.

While the motor was performing its journey, the stationary steam-engine
was employed in raising the pressure in the fixed cylinders to 63
atmospheres, and worked, on an average, during fifty minutes in each
hour; during the rest of the journey it remained idle. It was thus always
employed in doing work in excess of the pressure which could be utilized
on the car, and the work was, under the circumstances of the case,
necessarily intermittent. This was a very unfavorable condition of
working.

In the electric tram-car the haulage was effected by means of
accumulators. The car was of the ordinary type with two platforms. It was
said to have been running as an ordinary tram-car since 1876. It had been
altered in 1884 by raising the body about six inches, so as to lift it
clear of the wheels, in order to allow the space under the seats to be
available for receiving the accumulators, which consisted of Faure
batteries of a modified construction. The accumulators employed were of
an improved kind, devised by M. Julien, the under manager of the
Compagnie l'Electrique, which undertook the work.

The principal modification consists in the substitution, for the lead
core of the plates, of one composed of a new unalterable metal. By this
change the resistance is considerably diminished, the electromotive force
rises to 2.40 volts, the return is greater, the output more constant, and
the weight is considerably reduced. The plates being no longer subject to
deformation have the prospect of lasting i