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one pound of water at 212° the same temperature as the steam you added, and the temperature will only be raised about 2°. The one pound of steam heats six times more than the one pound of water, both being at the same temperature. This is the quantity of latent heat, which means simply hidden heat, in steam.

Proceeding further with the experiment, if, instead of allowing the steam to blow into the water, you confine it until it gets to some pressure, then blow it into the water, it takes the same weight to raise the temperature to the same degree. This means that the total heat remains practically the same, no matter at what pressure. This is James Watt's discovery, and it led him to the use of highpressure steam, used expansively.

Even coal may yet be superseded before it is exhausted, for as eminent an authority as Professor Pritchett of the Massachusetts Institute of Technology has said in a recent address:

Do you

Watt's invention and all it has led to is only a step on the way to harnessing the forces of nature to the service of man. doubt that other inventions will work changes even more sweeping than those which the steam engine has brought?

Consider a moment. The problem of which Watt solved a part is not the problem of inventing a machine, but the problem of using and storing the forces of nature which now go to waste. Now to us who live on the earth there is only one source of power-the sun. Darken the sun and every engine on the earth's surface would soon stop, every wheel cease to turn, and all movement cease. How prodigal this supply of power is we seldom stop to consider. Deducting the atmospheric absorption, it is still true that the sun delivers on each square yard of the earth's surface, when he is shining, the equivalent of one horse-power working continuously. Enough mechanical power goes to waste on the college campus to warm and light and supply all the manufactories, street railroads and other consumers of mechanical power in the city. How to harness this power and to store it—that is the problem of the inventor and the

engineer of the twentieth century, a problem which in good time is sure to be solved.

Who shall doubt, after finding this secret source of force in water, that some future Watt is to discover other sources of power, or perchance succeed in utilising the superabundant power known to exist in the heat of the sun, or discover the secret of the latent force employed by nature in animals, which converts chemical energy directly into the dynamic form, giving much higher efficiencies than any thermo-dynamic machine has to-day or probably ever can have. Little knew Shakespeare of man's perfect power of motion which utilises all energy! How came he then to exclaim "What a piece of work is man; how infinite in faculty; "in form and moving how express and admirable"? This query, and a thousand others, have arisen; for we forget Arnold's lines to the Master:

"Others abide our question. Thou art free.

"We ask and ask-thou smilest and art still."

Man's "moving" is found more "express and ad"mirable" than that of the most perfect machine or adaptation of natural forces yet devised. Lord Kelvin says the animal motor more closely resembles an electro-magnetic engine than a heat engine, but very probably the chemical forces in animals produce the external mechanical effects through electricity and do not act as a thermo-dynamic engine.

The wastage of heat energy under present methods

is appalling. About 65 per cent. of the heat energy of coal can be put into the steam boiler, and from this only 15 per cent. of mechanical power is obtained. Thus about nine-tenths of the original heat in coal is wasted. Proceeding further and putting mechanical power into electricity, only from 2 to 5 per cent. is turned into light; or, in other words, from coal to light we get on an average only about one-half of 1 per cent. of the original energy, a wastage of ninety-nine and one-half of every hundred pounds of coal used. The very best possible with largest and best machinery is a little more than one pound from every hundred consumed.

When Watt gave to the steam-engine five times its efficiency by utilising the latent heat, he only touched the fringe of the mysterious realm which envelops man.

Burbank, of the spineless cactus and new fruits, who has been delving deep into the mysteries, tells us:

The facts of plant life demand a kinetic theory of evolution, a slight change from Huxley's statement that, "Matter is a magazine of force," to that of matter being force alone. The time will come when the theory of "ions" will be thrown aside, and no line left between force and matter."

Professor Matthews, he who, with Professor Loeb at Wood's Hole, is imparting life to sea-urchins through electrical reactions, declares "that certain chemical sub"stances coming together under certain conditions are "bound to produce life. All life comes through the

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operation of universal laws." We are but young in all this mysterious business. What lies behind and probably near at hand may not merely revolutionise material agencies but human preconceptions as well. "There are more things in Heaven and Earth than are ever dreamt of in your Philosophy."

Latent Heat was a find indeed, but there remained another discovery yet to make. Watt found that no less than four-fifths of all the steam used was lost in heating the cold cylinder, and only one-fifth performed service by acting on the piston. Prevent this, and the power of the giant is increased fourfold. Here was the prize to contend for. Win this and the campaign is won. First then, what caused the loss? This was soon determined. The cylinder was necessarily cooled at the top because it was open to the air, and also cooled below in condensing the charge of steam that had driven the piston up in order to create a vacuum, without which the piston would not descend from top to bottom, to begin another upward stroke. A jet of cold water was introduced to effect this. How to surmount this seemingly insuperable obstacle was the problem that kept Watt long in profound study.

Many plans were entertained, only to be finally rejected. At last the flash came into that teeming brain like a stroke of lightning. Eureka! he had found it. Not one scintilla of doubt ever intruded thereafter. The solution lay right there and he would invent

the needed appliances. His mode of procedure, when on the trail of big game, is beautifully illustrated here. When he found the root of the defect which rendered the Newcomen engine impracticable for general purposes, he promptly formulated the one indispensable condition which alone met the problem, and which the successful steam-engine must possess. He abandoned all else for the time as superfluous, since this was the key of the position. This is the law he then laid down as an axiom-which is repeated in his specification for his first patent in 1769: "To make a perfect steam "engine it was necessary that the cylinder should be "always as hot as the steam which entered it, and "that the steam should be cooled below 100° to exert "its full powers."

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Watt describes how at last the idea of the "separate "condenser," the complete cure, flashed suddenly upon his mind:

I had gone to take a walk on a fine Sabbath afternoon, early in 1765. I had entered the green by the gate at the foot of Charlotte Street and had passed the old washing-house. I was thinking upon the engine at the time, and had gone as far as the herd's house, when the idea came into my mind that as steam was an elastic body it would rush into a vacuum, and if a communication were made between the cylinder and an exhausted vessel it would rush into it, and might be there condensed without cooling the cylinder. I then saw that I must get rid of the condensed steam and injection-water if I used a jet as in Newcomen's engine. Two ways of doing this occurred to me. First, the water might be run off by a descending pipe, if an offlet could be

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