to venture on the face of the waters in such dangerous and unseamanlike craft.  But go to Glasgow Bridge any day, and you will see how time has overcome fear and prejudice, for our ocean is covered with steamers of all sizes.  It is not many years ago since it was said that steamers could never reach America; this has given way to proof, and even Australia has been reached by steam.  I know of a steamer building which could carry the whole population of this place and not be full; she is 680 feet or 226 yards long, and a large vessel would hang like a boat alongside her.

The first attempt at giving motion by steam to ships was of course only in one way—­by a ratchet at the end of a beam, at one moment driving and the next standing still.  This was on account of the engine being only in power one half of the stroke; but by the double-acting engine being introduced, and the steam acting both ways, it became at last a steady mover (without the aid of two or three cylinders, as in the first engines, one to take up the other as the power was given off), by a ratchet on the end of a beam or else a chain.  This acted on the shaft which moved the paddles.  It is to Watt that we are indebted for the crank and direct action, so as to give a circular motion to the wheels.

We find in 1752 a Mr. Champion of Bristol applied the atmospheric engine to raise water to drive a number of wheels for working machinery in a brasswork, in other words, a foundry.  Also, in Colebrokedale, steam-engines were used to raise water that had passed over the wheel, so as to save water.  All these plans have, however, now passed by, like the water over the wheel, and we now have the engine the prime mover—­the double action of the steam on the piston, this acting on the 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.