ers of which were of
proportionately decreasing sizes, viz., 8.2 in., 5 in., 3.5 in., and 2
in., and the air on leaving each cylinder passed on its way to the next
cylinder through a coiled pipe immersed in flowing water to remove the
heat generated. This cooling surface amounted to nearly 54 sq. ft.

The cooling of the air was very efficient. In an experiment made on this
question, the temperature of the compressor did not vary to the extent of
9 deg. F. in charging the reservoir from 40 to 63 atmospheres, occupying an
hour and a half, the consumption of water during the time being about
1,400 gallons.

The fixed reservoirs were of about 240 cubic feet capacity.

The motor formed part of a compound vehicle, which may be said to have
consisted of two parts joined together by an articulated corridor, the
whole being covered by a roof which was approached from the platform
behind by an easy staircase. On this roof were seats for outside
passengers.

The front part of the compound vehicle contained the motor, as well as a
compartment for six inside passengers, with roof space for twenty
passengers, and weighed about 15,400 lb. when empty; the hind part
contained accommodation inside for twelve passengers, and outside for
fourteen passengers, and weighed 6,600 lb.

The combined vehicle was entered from the platform in the rear, which
could hold four passengers, and from thence, as already mentioned, the
staircase led on to the roof. The total number of passengers this vehicle
could accommodate was thus eighteen inside, thirty-four on the roof, four
on the platform, or fifty-six in all.

The total length of the carriage was 29 ft. 7 in., the width 7 ft. The
distance between the axes of the bogies was 16 ft. 9 in. The distances
apart of the centers of the wheels were in the case of the hind bogie 3
ft. 9 in., and in the case of the front bogie 4 ft. 4.6 in.

The motor is a compound engine, the diameters of the cylinders being 4.9
in. and 1.9 in., with a 12 in. stroke. The diameter of the wheels was 2
ft. 4 in. A small boiler is placed on one side, in front, for creating
steam, which passes into a steam-jacket, inclosing the pipe of
communication from the reservoir to the cylinders, as well as the
cylinders themselves, so that the air was warmed before it escaped. The
reservoirs on the motor contained 71 cubic feet.

In an experiment made on charging the reservoir in the motor, the
pressure in the fixed reservoirs, at