some time past been thoroughly satisfied that this fear was needless;
as I am satisfied that a well-made gas-engine is as durable as a
steam-engine, and the parts subject to wear can be replaced at
moderate cost. We have no boiler, no feed pump, no stuffing-boxes to
attend to--no water-gauges, pressure-gauges, safety-valve, or
throttle-valve to be looked after; the governor is of a very simple
construction; and the slide-valves may be removed and replaced in a
few minutes. An occasional cleaning out of the cylinder at
considerable intervals is all the supervision that the engine
requires.

The very large percentage of heat absorbed by the water-jacket should
point out to the ingenuity of inventors the first problem to be
attacked, viz., how to save this heat without wasting the lubricant or
making it inoperative; and in the solution of this problem, I look for
the most important improvement to be expected in the engine. The most
obvious contrivance would be some sort of intercepting shield, which
would save the walls of the cylinder and the rings of the piston from
the heat of the ignited gases. I have just learned that something of
the kind is under trial. Another solution may possibly be found in the
employment of a fluid piston; but here we are placed in a dilemma
between the liquids that are decomposed and the metals that are
oxidized at high temperatures. Next, the loss by radiation--15 per
cent.--seems large; but this is to be attributed to the fact that the
inside surface of the cylinder is at each inward stroke exposed to the
atmosphere--an influence which contributes to the cooling necessary
for lubrication. The remaining 15 per cent., which is carried away by
the exhaust, is small compared with the proportion passing away with
the exhaust steam of a high-pressure or the water of a condensing
engine. As the water in the jacket can be safely raised to 212° Fahr.,