358

Pressure Engines.

[Book III.

and closes the passages into the cylinder is analogous to that of steam en-gines, being effected by an eceentric on the crank shaft. It is omittedin the cut, that the essential features of the maehine might appear moreconspicuous.

It is obvious that engines of this kind may be employed to impart mo-tion to pumps or any other machinery. The intensity of the force trans-mitted by them depends upon the perpendicular height of the motivecolumn and the area of the piston. The use of the air vessel is, as in thehydraulic ram and other machines, to break the force of the blow or con-cussion consequent on the sudden stoppage of the descending column byclosing the passages. Wherever the Waste pipe B can descend thirty-five or thirty-six feet, the engine may derive an additional power from thevacuum thus kept up behind the piston, as in low-pressure steam-engines.The application of this feature to pressure engines was included in anEnglish patent granted to John Luddoek in February 1799. (Repertoryof Arts, vol. xi, page 73.)

The invention of pressure engines brought to light a new mode of em-ploying water as a motive agent; and also the means of applying it inlocations where it could not otherwise be used. When water moves anunder or overshot wheel, the machinery to be propelled must be placedin the immediate vicinity—hence saw, grist, and fulling mills, &c. areerected where the falling liquid flows ; and when steam is the movingforce, the engines are located where the fluid is generated ; but with pres-sure engines it is different, for the motive agent may be taken to the ma-chine itself. In valleys or low lands, having no natural fall of water, butwhere that liquid can be conveyed in tubes from a sufficient elevation, (nomatter how distant the source may be,) such water, by these machines,may be made to propel others. And by means of them the small lakesoften found on mountains, and water drawn from the heads of falls andrapids, may furnish power for numerous operations in neighboring plains.When cities are supplied from elevated sources, an additional revenuemight be derived from the force with which the liquid issues from thetubes : the occupant of a house into which a lateral pipe from the mainsis conveyed, might connect the pipe to a pressure engine, and therebyimpart motion to lathes, or printing presses ; raise and lower goods on dif-ferent stories ; press cotton, paper, books, &c. as by a steam-engine. Butunlike the machine just named, a pressure engine is inexpensive, and sim-ple in its construction—it requires neither chimneys, furnaces, nor loadsof fuel; neither Bremen nor engineers, nor is there any danger of explo-sions. It may be placed in the Corner of a room, or be concealed undera counter or a table. It may be set in Operation in a moment, by openinga cock, and the instant the work is done, it may be stopped by shuttingthe same, and thus prevent the least waste of power—and when the workis accomplished, the water can be used for all ordinary purposes as if justdrawn from the mains, for the engine might be considered as merely acontinuation of the lateral tube.

Pressure engines afford another illustration of the variety of purposesto which a piston and cylinder may be applied. These were probably firstused in piston bellows ; next in the syringe ; subsequently in pumps ofevery variety ; and then in pressure and steam-engines. The movingpiston is the nucleus or elemental part that gives efficiency to them all; andthe apparatus that surround it in some of them, are but its appendages.To what extent it is destined to be employed when steam becomes super-seded by other fluids, time only can reveal; but if we may judge of thefuture by the past, this simple device will perform greater wonders in the