sway beam, and the beam on the crank, which, by the assistance of the
fly-wheel on land or fixed engines, gives a uniform motion to the
machine. All these have now enabled us to apply the engine as our grand
moving power. One great and important point in the engine is the
governor, and the first modes of changing the steam from the top to the
bottom of the cylinder were cumbrous, till the excentric wheel was
devised.

Boilers also have to be attended to--these were at first rude and now
would be useless. They were unprovided with valves, gauge-cocks, or any
other safety, all of which are now so well understood that nothing but
carelessness can cause a blow-up. One of the greatest causes of danger
is that of letting there be too little water in the boiler, and thus
allowing it to get red-hot, when, if you let in water, such a volume of
steam is generated that no valve will let it escape fast enough. Force
or feed pumps are also required to keep the water in the boiler at a
proper height, which is ascertained by the gauge-cocks. Mercury gauges
for low pressure act according to the pressure of the atmosphere;
high-pressure boilers of course require a different construction, as the
steam is greater in pressure than the air.

Having got so far in my subject, I think before concluding I must devote
a short time in showing the first steps of the locomotive; the more so,
as I am speaking to those who are so largely engaged in the daily
working of that now beautifully perfect machine. Various and for a time
unsuccessful experiments were made to bring out a machinery or
travelling engine, as it was first called. A patent was taken by a Mr.
Trevethick for a locomotive to run on common roads, and to a certain
extent it did work. An amusing anecdote is told of it. In coming up to a
toll-gate, the gatekeeper, almost frightened out of his seven senses,