The Hydraulic Press was invented by Mr. Bramab, and is a machine of very great power in compressing bodies weights ; or, again, in drawing up trees by the roots, or piles from the beds of rivers. There is an. iron cylinder in which a piston works. At the bottom of the former is inserted a tube, whose aperture, under the, piston, is covered by a valve. The other end of the tube communi cates with a small forcing pump, by which water is driven through the said valve into the lower part of the cylinder, where its hydrosta tical action is exerted to raise up the piston. Now suppose the diameter of the cylinder to be 10 inches, and that of the piston in the forcing pump to be one quarter of an inch, then the proportion between the surfaces of the pistons will be that of 1600 to 1; and, on the principle of the equal pressure of fluids in every direction, the force with which the lar ger piston is raised bears the same proportion to the resistance against the lower'surface of that in the' forcing pump.
The largest and finest hydraulic presses ever constructed, were those made'by Easton 'and Amos, and employed in raising the ponderous tubes of the Britannia Bridge. The ram or larger piston is 22 inches in diameter ; the cylinder in which it worked is 9 feet long by six inches thickness of metal ; and one of the castings for making the largest press required 21 tons of melted iron.
In water wheels, water is made" to act as a moving power against wheels by its weight, its momentum, or by both combined. In the first case the wheel is provided with a number of buckets, ortroughs, into which the water is received near the level of the axle of the wheel; the vessels thus filled becoming hea vier than those on the other 'side', the wheel is made to revolve by that excess of weight merely. But if the water fall into the troughs
from a channel on a level Nviththe top of the wheel, or at least above the axle, the wheel will revolve both" by the weight and by the momentum which the water acquires by its fall. This is called an overshot wheel. If the lower part of the wheel be placed in a stream of water which is made to act on float-hoards fixed on the circumference, the machine has the name of an undershot wheel. Lastly, when the wheel is placed in a sort of channel, or race, as it is called, which is formed between two projections of masonry below the bed of the upper portion of the stream, and so as to coin cide very nearly with the lower quadrant of the wheel's circumference on that side, the water descending from the stream upon float boards, or troughs, and thus acting both by its momentum and weight, the machine is called a breast wheel. It has been determined by experiment that the effect of the wheel is the greatest when its velocity is about half the velocity of the stream ; and it is asserted that the efficacy of an overshot wheel is more than double that of an undershot wheel of equal magnitude.
A remarkable application of water power has been recently made in the United States, to work the printing press of a daily paper in Boston. Through a two inch lead pipe, a stream of water is introduced into a meter, which only occupies twenty-four square inches. 1 The fall of water between the Boston reser ; voir and this meter is about a hundred feet. This two-inch stream will discharge eighty I gallons of water each minute, and in passing through the meter will give a motive power equal to what is called three-horse power. This is more than sufficient for driving the press.