But the rediscovery of this law, as a result of experiment, is due to English physicists of our own day; and it is so invariably true, and the produced force is always so perfectly proportioned to the force producing it, that some [Footnote 9] have gone so far as to revive a very old hypothesis in philosophy, supposing that all the forces of nature are but differently expressed forms of the Divine Will.
[Footnote 9: Dr. Carpenter, Philos. Trans. 1840, vol. ii. ]
As a corollary to this law, it follows that many a force of nature, hitherto neglected because of its position or intractability, may be turned to practical account by using it to produce some new power, which may be either stored up or transmitted to a distance, and so can be employed wherever and whenever it is required. Thus, in the first machine we propose to notice, a M. Cazal has just hit upon a plan by which to use the power of falling water at a considerable distance. He employs a water-wheel to turn a magneto-electric machine (of the kind used for medical purposes, on a very large scale), and the electric force so obtained may be conveyed to any distance, and employed there as a motive power. In this way a mountain stream in the Alps or Pyrenees may turn a lathe, or set a loom in motion, in a workshop in Paris or Lyons; or even (as has been remarked), if a wire were laid across the Atlantic, the whole force of Niagara would be at our disposal.
The idea is at present quite in its infancy; but we are told that the few experiments hitherto made show that such an engine is not only very ingenious but perfectly feasible, and (most important of all) economical.
The second engine gave promise of considerable success when first brought out in Paris about eight months ago. It was invented by a M. Tellier, and proceeds on the principle of storing up force, to be used when wanted. It has long been well known to chemists that a certain number of gases (as chlorine, carbonic acid, ammonia, and sulphuretted hydrogen) can be condensed into liquids by cold or pressure, or both combined. Of all these gases, ammonia is the most easily liquefied, requiring for this purpose, at ordinary temperatures, a pressure only six and a half times greater than that of the atmosphere. A supply of liquid ammonia obtained in this manner is kept by M. Tellier in a closed vessel, and surrounded with a freezing mixture, so that it has but little tendency to return to the gaseous state. A small quantity is allowed to escape from this reservoir under the piston of the engine, and, the temperature there being higher than in the reservoir, the ammonia becomes at once converted into gas, increasing thereby to more than twelve hundred times its previous bulk, and so driving the piston with great force to the top of the cylinder. A little water is now admitted, which entirely dissolves the ammonia, a vacuum being thus created, and the piston driven down again by the pressure of the air without. M. Tellier employs three such cylinders, which work in succession; and the only apparent limit to the power to be obtained from this machine is the amount of liquid ammonia which would have to be used, about three gallons (or twenty-two pounds) being required for each horse-power per hour. There is no waste of material; for the water which has dissolved [{31}] the gas is saved, and the ammonia recovered from it by evaporation, and afterwards condensed into a liquid. M. Tellier proposed to use his engine for propelling omnibuses and other vehicles; but it would appear that it is too expensive and too cumbrous to be practically useful; there can, however, be very little doubt that the principle will be used with success in some new form. A patent has quite recently been taken out for such an engine in England. It will be perceived at once how the ammonia engine illustrates the law of storing up force. It originates no power of its own, but simply gives out by degrees the mechanical force which had been previously employed to change the ammonia from a gas to a liquid.
Lenoir's "gas-engine" has been more successful; for, although but a few months old, it has been already largely adopted in Parisian hotels, schools, and other large establishments, for raising lifts, making ices, and even--for what is not done now-a-days by machinery?--cleaning boots. In London, it was lately exhibited in Cranbourne Street, and is now used for turning lathes and for other light work.
This engine, like the ammonia-engine, is provided with an ordinary cylinder, into which coal-gas and air are admitted, under the piston, in the proportions of eleven parts of the latter to one of the former. The mixture is then exploded by the electric spark, and the remaining air, being greatly expanded, drives up the piston. When the top is reached the gas and air are again admitted, but this time above the piston, and the explosion is repeated, so that the piston is driven down again. The most ingenious part of the whole thing is the mechanism by which the electric spark is directed alternately to the upper and lower ends of the cylinder. This cannot be satisfactorily explained without a diagram, but is brought about (roughly speaking) by connecting either end of the cylinder with a semicircle of brass, which is touched by the "rotary crank" in the course of its revolution. The crank is already charged with electricity, and so communicates the electric spark to each of the semicircles in turn. The cylinder is kept plunged in water, so that there is no fear of its overheating by the constant explosions.
This engine has cheapness for its main recommendation. A half-horsepower gas-engine (the commonest power made) costs, when complete, £65, and consumes twopence worth of gas per hour; while the cost of keeping the battery active is about fourpence per week.
An engineer of Lyons, M. Millon, has since proposed to use, instead of coal-gas, the gases produced by passing steam over red-hot coke. These gases are found to explode rather more quickly than coal-gas, when mixed with common air, and fired by the electric spark. They will probably be found cheaper and more efficient when they can be obtained; but in many cases coal-gas will be the only material available.
A M. Jules Gros has recently invented an engine in which gun-cotton is exploded in a strong reservoir and air compressed in another, the compressed air being afterward employed to move the pistons of the machine. This sounds more dangerous than it perhaps really is, since gun-cotton is now known to be more tractable than gunpowder, when properly used; but we very much doubt whether the machine can be regular or economical enough to be more than a curiosity.