licity of the
machinery.

Various sizes of engines, of different degrees of strength and weight,
have been tried, and it is found that a fire-engine with two cylinders
of 7 inches diameter, and a stroke of 8 inches, can be made
sufficiently strong at 17-1/2 cwt. If 4 cwt. be added for the hose and
tools, it will be found quite as heavy as two fast horses can manage,
for a distance under six miles, with five firemen and a driver.

[Illustration: FIG. 1. Fire-Engine used by the London Fire Brigade.
Longitudinal section,--with the Levers turned up for travelling.]

This size of engine has been adopted by the Board of Admiralty and the
Board of Ordnance, and its use is becoming very general.

When engines are made larger, it is seldom that the proper proportions
are preserved, and they are generally worked with difficulty, and soon
fatigue the men at the levers.

[Illustration: FIG. 2. Transverse section.]

When an engine is large, it not only requires a considerable number of
men to work it, but it is not easily supplied with water; and, above
all, _it cannot be moved about with that celerity on which, in a
fire-engine establishment, everything depends_. When the engine is
brought into actual operation, the effect to be produced depends less
on the quantity of water thrown than upon its being made actually to
strike the burning materials, the force with which it does so, and the
steadiness with which the engine is worked. If the water be steadily
directed upon the burning materials, the effect even of a small
quantity is astonishing.

When a large engine is required in London, two with 7-inches cylinders
are worked together by means of a connecting screw, thus making a jet
very nearly equal (as 98 to 100) to that of an engine with cylinders
10 inches diameter.

It is also an advantage not unworthy of consideration, that two 7-inch
engines may be had nearly for the price of one 10-inch one; so that if
one happens to be rendered unserviceable the other may still be
available.

The usual rate of working an engine of the size described is 40
strokes of each cylinder per minute; this gives 88 gallons. The number
of men required to keep steadily at work for three or four hours is
26; upwards of 30 men are sometimes put on when a great length of hose
is necessary. The lever is in the proportion of 4-1/4 to 1. With 40
feet of leather hose and a 7/8 inch jet, the pressure is 30 lb. on the
square inch; this gives 10.4 lb