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.'"