The situation of the machine as represented in Fig. 7, is as follows. The regulator is open, as appears by its plate TY, being removed from under the com munication or throat pipe SS that goes into the cylin der. The piston is now at the place CW, Fig. 6, at the top of the cylinder, and consequently the great beam it h and the working perpendicular beam QQ are now almost at their utmost height: And the pul ley P in the slit of the working beam has so far raised the spanner h 5 that the weight F is brought so much from beneath N as to be past the perpendicular over the axle AB ; and being ready to fall over towards N, it will with a smart blow of its shank E strike the pin L, and drawing the fork OL horizontally towards the working beam, will draw the end 10 of handle of the regulator towards 1, and then shut it by slip ping the plate V under the pipe SS. In Fig. 6, the blow is already struck, as may be seen by observing that the weight at the head of the Y has got to 6, as far as the strap P 6 (or n 6 in Fig. 7.) will let it go.
When the regulator is shut, the next thing is to open the injection cock to produce the vacuum, and immediately to shut it when the piston begins to come down. The part of the pipe coming from the inject ing cistern is shown at o, Fig. 7, and c is the part that leads to the cylinder, e is the key of the cock which has a narrow long upright hole, instead of a round one, that it may be the sooner opened. On the top of this key there is fastened a quarter of a toothed wheel 1, turned by another quarter of a toothed wheel i hanging down from the axis h g, which is moved by the lever h le, commonly called the F.
As soon as the regulator is shut by the ascent of the pulley p, the beam QQ not immediately losing its motion upwards, the pin s on its outside lifts up the extremity 1 of the F, 1 k h, and opens the injection cock ; and the jet immediately making a vacuum, the beam begins to descend, and the pin r which can be put higher or lower, depressing the F shuts the injec tion cock ; while the beam QQ continuing to descend, the pulley p pressing on the handle C 4, throws back the Y, whose shank 1) throws forward the fork and opens the regulator to admit fresh steam in the way formerly described, which steam is shut off by shut ting the regulator till the injecting cock is agair/ opened.
In the engine represented in Fig. 6. there is a strong frame F 1 F 2, upon which fill two strong wooden springs. S 1 S 2, that if the arch of the great beam h h should come down too low, no mischief may be done to the piston, and the whole stroke may be made upon S 1 S 2 by the strong iron pins P 1 P 2, which will there lie stopped. The pump which the engine is to work, is shown at p, the pump rod at i, and k is the rod of another pump which raises some of the water at p, by the injection reservior A., through a pipe which
passes by o, and behind the attendant c.
Hitherto the steam employed as a mechanical power had been reconverted into water by condensation ; but about the year 1720, Leopold, the author of the Thea tram Machinarum, suggested the plan of blowing it out into the atmosphere, and may therefore be consider ed as the inventor of the high pressure engine. This engine is shown in Fig. 1 of Plate DV1, where A is the boiler communicating by the four way cock X with the lower ends of two cylinders R,S, in which two pistons C,D move up and down, and put in motion two levers G,H by the intervention of the piston rods, E,F. Pump rods K,L, fixed to the other ends of these levers, work the pumps 0 and P, and raise the water up the main pipe Q. The fire-place is shown at Z, and the ash-pit at Y. The levers G,H move upon pivots LI, and the four way cock X is so con structed as to shut off the communication between the boiler A and either of the cylinders R,S, while it opens a communication with the external air. The operation of the engine is as follows.
The steam from the boiler A being admitted through the passage 3 into the cylinder R, forces the piston C up to the top, and thus depresses the pump rod K, which forces the water up Q. When C is at the top, the cock X is turned, and the passage B between the boiler and the cylinder closed, while a communication is opened from the inside of the cylinder into the at mosphere. The weight of the piston and piston rod FG, being made greater than that of K and 0, the piston C will fall to the bottom of the cylinder, driving out the steam that had remained in it From the con struction of the cock X a passage is opened between the boiler A and the other cylinder S, when the pas sage into R was closed. Hence the piston D is forced upwards, and the pump rod of the pump P descends and forces water up Q. The cock X being again turned, the steam is shut off from S, and a passage open into the external air, so that the weight of ED being greater than that of LP, the piston D will de scend and press out the steam into the atmophere.
No attempt had yet been made to emir( rt the reci procating motion of the piston into a continuous rota tory motion ; but Mr. Jonathan Hulls, who in 1736 proposed to apply the steam engine to tow vessels or ships into and out of harbour, described a contrivance by which the rise and fall of the piston should give a continued t otatory motion to the paddle wheels, but the proposal excited no notice ; and his steam boat as well as his rotatory mechanism,` were left as a legacy to his successor. See our article STEAM BOAT.