The first vessel P being thus emptied of its air, open the cock again, and the force of steam from the. boiler presses upon the surface of the water with an elastic quality like air, still increasing in elasticity or spring, till it counterpoises rather exceeds the weight of water ascending in the pipe S, out of which the contained water will be immediately discharged when once gotte; to the top, which takes up some time to recover that power; but having once got it, and being in work, it is easy for one that never saw the engine, after half an hour's experience, to keep a constant stream running out the full bore of the pipe. On the outside of the vessel you may see how the water goes out, as well as if the vessel were transparent ; for as flr as the steam continues within the vessel, so far is the vessel dry without, and so very hot as scarcely to endure the least touch of the hand. But as far as the water is, the said vessel will be cold and wet where any water has fallen on it, which cold and moisture vanish as fast as the steam, in its descent, takes place of the water; but if you force all the water out, the steam, or a small part thereof, going through P, will rattle the clack, so as to give sufficient notice to change the cocks, and the steam will then begin to force upon the other vessel, without the least alteration in the stream ; only sometimes the stream of water will be somewhat stronger than before, if you change the cocks before any considerable quantity of steam be gone up the clack R: but it is better to let none of the steam go off, for that is losing so much strength, and is easily prevented by altering the cocks some little time before the vessel is emptied.
The wood-cut represents two reservoirs, P P, designed for alternate action ; the tube E conveys water from the discharging pipe, to replenish the boiler L, when the water in it begins to be almost consumed ; and this is done by keeping D supplied with water, and (lighting the fire at B) generating a sufficiency of steam to press the water into L, through the pipe K. This will convey a tolerably correct idea of Savery's engine, and the mode of its operation. He gives no proportions of its parts, nor perhaps had he established any rule of action. He appears to have considered the strength of his machine to be the only Unlit to be observed ; " for," says he, " I will raise you water 500 or 1000 feet high, could you find us a way to procure strength enough for such an immense weight as a pillar of water of that height. But my engine, at 60, 70, or 80 feet, raises a full bore of water ifith much ease." The structure of this engine presents a good deal of rude and primitive simplicity ; but at all events, his claims to original invention, in applying the two great forces of steam—its expansion and contraction—and in presenting the world with the first effective steam-engine, under this combination, are of the highest class. These claims begat, as might be supposed, a good deal of detraction ; and Savery has been assailed with much more severity than justice. The limits of an article of this kind will not admit of a detailed narration of the attacks brought against his reputation as an inventor ; it is, however, sufficient to notice, that Dr. Desaguliers accuses him of plagiarising the ideas of
Lord Worcester; and in support of this alleged act of dishonesty, broadly charges him with buying up and destroying all the copies of the Marquess's book. But it will have been seen that the account therein given of the "fire water work," rather contains more to puzzle than to enlighten the mechanic„ beyond the mere announcement of steam in its expansive state being available as an effective mechanical force. Not a word implies the action of steam under condensation, which constitutes the chief merit of Savery's invention, (apart from the credit of having constructed and published a working engine) ; nor is there the remotest suggestion conveyed for the fabrication of a machine similar to that which the Marquess vaguely described. The evidence as to buying up the. copies of his lordship's work is exceedingly slender ; but if it were undeniable, it would attest but a venial act of personal vanity on Savery's part.
The accusation, however, is Important to Savery's fame, by indirectly supporting his claims to originality ; for, at the same period that be was prosecuting his efforts, Dr. Denys Papin, a Frenchman of considerable eminence, was engaged in experiments and attempts of a similar tendency. Savery could buy up the Marquess's books, but he could not buy up Papin, nor the results of that philosopher's speculations, originated by the Marquess of Worcester.
Papin had invented a mode of softening bones, by submitting them to the action of steam of high temperature, in a boiler or digester, which ultimately led him to the consideration of steam as a motive force. In 1685, he exhibited a model of a machine for raising water, and "propounded it as a riddle, to stir up those that are ingenious in the same kind of learning, and make them find sometimes better things than what is propounded." He subsequently gave a description of this model, from which it appeared that the water was raised by rarefying the air in the vessel into which it was impelled, by the pressure of the atmosphere on the water in the cistern. The mode by which he rarefied the air was carefully concealed. In two of the solutions given, the same effect was produced by condensing it. Though a person of great reputation in England, he was not successful in his attempts to obtain encouragement in carrying his suggestions into effect. In 1687 he was employed to erect machines constructed on his principle, for draining mines ; but the result, as predicted by Dr. Robt. Hooke and others, was an entire failure. After a number of ingenious plans proposed subsequently, and the application of gunpowder fur producing a vacuum, he at length conceived the possibility of effecting the object in view, namely, draining mines, by means of condensing steam in a cylinder, and so producing the vacuum he had in vain essayed to form by other modes.