water the vapour will rapidly condense; and the minute particles of which it is composed will return to their original bulk. A vacuum being thus formed within the vessel, the piston will be driven into the tube with a force proportionate to its diameter; the atmosphere or air that surrounds it pressing with a weight equal to about fifteen pounds on each inch of its entire surface. On the heat being again applied, the process may be repeated with a similar result.

If the glass tube be lengthened, and bent in the form of an inverted U, or syphon, with the lower leg immersed in an open reservoir of water, thirty feet below the heated bulb, it will be found after a repetition of the process of condensation, that the pressure of the atmosphere, acting upon the surface of the water, will so far tend to fill up the vacuum, as to raise the water contained in the open reservoir to the top of the vessel; and it is upon this latter principle, that Savery's first engines were constructed; the remaining lift being effected by the repellent force of steam. As, however, we propose in this part of the work, to confine ourselves more particularly to the historical data, connected with the early history and invention of the steam engine, without reference to the more immediate principles of its construction and application, it may be enough to say, that an engine for raising water on this plan, has lately been contrived by Mr. Pontifex, of Shoe Lane, which for economy in the use of fuel, and in expense of erec

tion, offers very considerable advantages over any yet employed.

In 1698, Captain Savery obtained a patent for a new mode of raising water, and communicating motion to a variety of machines by the force of steam; and in the following year a working model of the above engine, was submitted to the Royal Society, who then held their sittings in Arundel House.* Savery's engine as we have already stated, was employed to raise water to a given height by the pressure of the atmosphere, and then to force the fluid up the remaining elevation, by the power of steam acting on the surface.

In the engines constructed under the authority of Savery's patent, it was necessary for a labourer to be in constant attendance for the purpose of turning the cocks, which alternately admitted steam and the condensing water. M. de Moura however effected a considerable improvement in this part of the engine, by constructing a self-acting apparatus for this purpose.

One of the greatest objections to this engine, was the extreme danger attendant on raising

*The following notice of this machine is inserted in their Transactions for that year.

"Mr. Savery, June 14, 1699, entertained the Royal Society, with shewing a small model of his engine for raising water by the help of fire, which he set to work before them. The experiment succeeded according to expectation, and to their satisfaction.'

water to any height beyond the atmospheric pressure; and as this seldom exceeded thirty feet, it was necessary for the remaining perpendicular lift to be effected by the expansive force of steam, upon the same principle as the Marquis of Worcester's engine, and for every thirty-three or four feet beyond that height, a pressure equal to the atmosphere must be exerted on the inside of the boiler and receivers, tending to burst them open. On this account it would require a separate engine, for every fourteen fathoms of the depth of a mine, thus raising the water from one to another; but in the event of any one becoming deranged, the whole must necessarily stop.

From this it will be seen, that this engine was not adapted either for the supply of towns or the draining of mines, (two of the patentee's principal objects,) the latter of which were often of considerable depth; but a number of small ones were erected for the raising of water in gentlemen's pleasure grounds, in different parts of England. Dr. Desaguliers tells us that he made seven of these engines the first was for the Czar, Peter the Great, for his garden at Petersburgh, where it was set up. The boiler was made spherical, and held between five and six hogsheads. The receiver held one hogshead, and was filled and emptied four times in a minute. The water was drawn up by suction, or the pressure of the atmosphere, twentynine feet high out of the well, and then pressed

up eleven feet higher. The pipes were all of copper, but soldered to the suction piece with soft solder, which held very well for that height. Had, however, the amount of pressure been greater, it must have burst the metal, and produced the most mischievous effects.

From a MS. in the possession of the late Rev. Mr. Stebbing Shaw, it appeared that Savery erected one of these about the close of the seventeenth century, at Wednesbury, in the county of Stafford. In this place the water rose so rapidly and in such quantities, from an adjacent coal pit, that it covered several acres of ground, where it remained for several years, although every effort was made to reduce it, and drain the land.

It was soon found that the mode of producing a vacuum in these engines was liable to the most serious objections, not the least of which was the unnecessary waste of steam; and an improvement on the original construction was shortly effected, which, although not capable of completely correcting this defect, produced a considerable saving in the amount of fuel employed.

It has been already stated, that Savery's mode of condensation consisted in throwing a quantity of cold water on the outside of the steam vessel employed to form a vacuum in the pipes; and on the re-admission of steam it was found necessary to restore the heat previously absorbed. To prevent this, a small jet was inserted, which striking

water to any height beyond the atmospheric pressure; and as this seldom exceeded thirty feet, it was necessary for the remaining perpendicular lift to be effected by the expansive force of steam, upon the same principle as the Marquis of Worcester's engine, and for every thirty-three or four feet beyond that height, a pressure equal to the atmosphere must be exerted on the inside of the boiler and receivers, tending to burst them open. On this account it would require a separate engine, for every fourteen fathoms of the depth of a mine, thus raising the water from one to another; but in the event of any one becoming deranged, the whole must necessarily stop.

From this it will be seen, that this engine was not adapted either for the supply of towns or the draining of mines, (two of the patentee's principal objects,) the latter of which were often of considerable depth; but a number of small ones were erected for the raising of water in gentlemen's pleasure grounds, in different parts of England. Dr. Desaguliers tells us that he made seven of these engines the first was for the Czar, Peter the Great, for his garden at Petersburgh, where it was set up. The boiler was made spherical, and held between five and six hogsheads. The receiver held one hogshead, and was filled and emptied four times in a minute. The water was drawn up by suction, or the pressure of the atmosphere, twentynine feet high out of the well, and then pressed