Thus each of the vessels V V′ is alternately filled from S, and the water thence forced into F. The same steam which forces the water from the vessels into F, having done its duty, is condensed, and brings up the water from S, by giving effect to the atmospheric pressure.

During this process, two alternate motions or adjustments must be constantly made; the communication between T and the boiler must be opened, and that between T′ and the boiler closed, which is done by one motion of the regulator. The condensing pipe at the same time must be brought from V to play on V′, which is done by the lever placed upon it. Again [Pg056] the communication between T′ and the boiler is to be opened, and that between T and the boiler closed; this is done by moving back the regulator. The condensing pipe is brought from V′ to V by moving back the other lever, and so on alternately.

For the clearness and convenience of description, some slight and otherwise unimportant changes have been made in the position of the parts. A perspective view of this engine is represented at the head of this chapter. The different parts already described will easily be recognised.

The engine of Savery was very clearly described in a small work published in London in 1702, entitled, The Miner's Friend, or an Engine to raise Water by Fire described, and the Manner of Fixing it in Mines; with an Account of the several Uses it is applicable unto, and an Answer to the Objection made against it; by Thomas Savery, Gentleman. This volume was dedicated to William III. (to whom the engine had been exhibited at Hampton Court palace), to the Royal Society, and to the mining adventurers of England. The following are the uses to which Savery proposed the engine should be applied: First, to raise water for turning all sorts of mills; second, supplying palaces and houses with water, and supplying means of extinguishing fire therein by the water so raised; third, the supplying cities and towns with water; fourth, draining fens or marshes; fifth, for ships; sixth, the drainage of mines.

Dr. Harris, in his Lexicon Technicum, or Dictionary of Arts and Sciences, mentions a machine of Savery's for propelling a vessel in a calm, by paddle-wheels placed at the side; but it does not appear that Savery contemplated the application of a steam engine to work these wheels.

It is only from scattered passages in publications of the day that it can be ascertained to what extent the engines of Savery were practically applied. In his address to the Royal Society, he speaks of the "difficulties and expense which he encountered in instructing artisans to make engines according to his wish; but that after much experience the workmen had become such masters of the thing, that they bound themselves to deliver the engines 'exactly tight and fit for [Pg057] service, and such as he (Savery) dare warrant them to every one that has occasion for them.'"

In his address to the miners of England he also says, "that the frequent disorders and cumbersomeness of water engines then in use encouraged him to invent engines to work by this new force; that though they were obliged to encounter the oddest and almost insuperable difficulties, yet he spared neither time, pains, nor money, till he had conquered them."

In Bradley's Improvements of Planting and Gardening, 1718, the author thus speaks of an engine erected by Savery:—

"Supposing the situation of a house or garden to be a considerable height above any pond, river, or spring, and that it has at present no other conveniency of water than what is brought continually by men or horses to it. In this case, the wonderful invention of the late Mr. Savery, F.R.S., for raising water by fire, will not only supply the defect, by flinging up as much water as may be desired, but may be maintained with very little trouble and very small expense.

"It is now about six years since Mr. Savery set up one of them for that curious gentleman Mr. Balle, at Cambden House, Kensington, near London, which has succeeded so well that there has not been any want of water since it has been built; and, with the improvements since made to it, I am apt to believe will be less subject to be out of order than any engine whatever."