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. Do you 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 admirable" 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.