356

Westgarth’s Pressure Engine.

[Book III.

Suppose the water in A has a perpendicular fall of thirty-four or thirty-five feet, and it were required to raise a portion of it to an elevation ofseventy feet above F; it will be apparent that if both pistons were oftlie same diameter, such an object could not be accomplished by this ma-chine—for both cylinders would virtually be but one—and so would thepistons ; and the pressure of the column on both sides of the latter wouldbe equal. A column of water tbirty-five feet high presses on the base thatsustains it with a force of 151bs. on every superficial inch; and one ofseventy feet high, with a force of 301bs. on every inch—hence without re-garding the friction to be overcome, which arises from the rubbing of thepistons; from the passage of the water through the pipes: and from the ne-cessar y apparatus to render the machine self-acting—it is obvious in the casesupposed that the area of the piston in C must be more than double thatin D, or no water could be discharged through B. Thus in all cases, therelative proportion between the area of the pistons, or diameter of the cy-linders, must be determined by the difference between the perpendicularheight of the two columns. When the descending one passes through aperpendicular space, greatly exceeding that of the ascending one, thenthe cylinder of the latter may be larger than that of the former : a smallerquantity of water in this case raising a larger one : it, however, descendslike a small weight at the long end of a lever, through a greater space.

In 1769 the London Society of Arts, awarded to Mr. Westgarth a pre-mium of fifty guineas, for his invention of a pressure engine. It is des-cribed by the celebrated Smeaton, in vol. v, of their Transactions, as “oneof the greatest strokes of art in the hydraulic way, that has appeared sincethe invention of the fire [steam] engine.” Several were erected byMr. W. in 1765, to raise water from lead mines in the north of Eng-land. They were simple in their construction, and somewhat resembledthe engines of Newcomen. They differed from those of Belidor in theposition of the cylinder; the introduction of a beam; the Substitution ofcylindrical valves in the place of cocks ; and using the motive column tomove the piston in one direction only. The cylinder of Westgarth’s en-gine was placed in a vertical position, the piston rod of which was sus-pended by a chain from the arched end of a “ walking” or vibrating beam;while the other end of the latter, projected over the mouth of the mine orpit, and was connected (by a chain) to the rod of an atmospTieric pumpplaced in the pit. This rod was loaded as in Newcomen’s engine, so asto descend by its weight and thereby raise the piston of the pressure en-gine when the column of water was not acting on the latter. Thus, whenthe motive column of water was admitted into the cylinder, the pistonwas depressed, and the end of the beam also, to which it was connected;consequently the pump rod a,nd its sucker were raised, and with themwater from the mine. Then as soon as the piston reached the bottom ofthe cylinder, the motive column was cut off, by closing a valve ; and apassage made for the escape of that within the cylinder, by openinganother—upon which the loaded pump rod again preponderated—thevalve to admit the column on the piston of the pressure engine was againopened, and the Operation repeated as before.

In another form these machines have been adopted, in favorable loca-tions, as first movers of machinery, and when thus used, they exhibit avery striking resemblance to high pressure steam-engines. tndeed, theelemental features of steam and pressure engines are the same, and themodes of employing the motive agents in both are identical—it is the dif-ferent properties of the agents that induces a slight Variation in the ma-chines—one being an elastic fluid, the other a non-elastic liquid. In steam-