Page:Popular Science Monthly Volume 15.djvu/314

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may be required for service; for it may be made to coil a spring, to raise heavy weights, or lift water into elevated reservoirs, or, by other simple devices well known to the mechanical engineer, to store up its power, which may be subsequently given out through machines especially adapted for the purpose.

The tides ebbing and flowing twice daily, lifting upon their bosom, like so many corks, the heaviest vessels, and baffling all efforts to restrain their resistless force, afford us another instructive topic for consideration in treating of the wasted forces of Nature—for here, again, she has lavished out of her superabundance infinitely more power than any conceivable increase of the needs and industries of man could ever employ.

The rise and fall of the tides vary, according to local conditions, from a few inches, as in the Mediterranean Sea, to seventy feet, as in the Bay of Fundy, and their force in almost any one of our rivers would, if properly applied, suffice to furnish ample power to all the mills and factories and workshops that could be built side by side upon their banks. They would drive under-shot wheels unfailingly. Where there are extensive meadows regularly overflowed, as they commonly exist along all of our larger streams, a levee containing two sluices, each supplied with a turbine water-wheel, one to be driven by the ebb and the other by the flow, could be made to utilize incalculable power.

In some exceptionally favorable localities, where the conditions have forced themselves upon the attention of observing and practical men, tide-motors have been introduced, and with great advantage; but the general utilization of these exhaustless and continuous stores of energy still remains to be accomplished.

Great rivers above tide-water are rolling down a wealth of power in their currents; and a hundred factories along their banks, heedless of the fact, are using steam-power. And it is one of the standing marvels that manufacturers fail to recognize the elementary fact in mechanics, that it is not necessary for a stream to have from ten to two hundred feet of fall, in order to do their work; while the great rivers upon whose banks their workshops are perched are permitted heedlessly to pour out trillions of cubic feet of water, year after year, into the ocean, opposing no mechanical difficulties in the way of yielding up their inexhaustible supplies of power.

Who may estimate the wealth of power poured out in unheeded profusion by our great waterfalls from Niagara down? Confining our attention to the one grand cataract, try to conceive of two million tons of water per minute hurled down that ledge of rock, representing 50,000 horse-power expended every minute in the work of disintegrating and undermining the rocky river-bed below. A few tiny paddles, I am told, dip into the current above the falls, and drive a paper-mill, but what of the millions of horse-power that are allowed