rare on booksellers' shelves thirty-five years after its publication, is not at all an extraordinary circumstance, and it would, indeed, have been a miracle had a copy, of any equally unimportant book, been found at such a distance of time in that unenviable situation.*

Savery exhibited a model of his engine before King William at Hampton Court; and the success of the experiment appeared so satisfactory, that the King warmly interested himself in the project. It was not until June 1699, a year after he had obtained his patent, and erected some engines, that he made trial of his engine before the Royal Society. In his address to that body, prefixed to his Miner's Friend, in 1702, he mentions the great "difficulties and expense he had incurred to instruct persons to frame his machine; but that he had at last succeeded in getting workmen, who would oblige themselves to make engines, exactly tight and fit for service; so that he could warrant them to those who chose to employ them." +

"The first thing," says the ingenious inventor, "is to fix the engine (the Tenth Figure) in a good double

* "When the Marquis's loose and vague description is recollected, and that he does not descend into the minutiae of executive construction; there appears to be no strong reason for depriving the captain of the title of an inventor!" Crit. Nat. Philos. p. 253.

"In Lord Worcester's time the machine was not practically introduced, and it was soon forgotten. Savery's engines were constructed in a manner precisely similar, and it is uncertain whether he adopted the Marquis of Worcester's ideas, or re-invented a similar machine.' Dr. Thomas Young, Nat. Phil.

Vol. 1, p. 356

furnace, so contrived that the flame of your fire may circulate round, and encompass your two boilers, as you do coppers for brewing. Before you make any fire, unscrew G and N, being the two small gauge pipes and cocks belonging to the two boilers, and at the holes fill L,* the great boiler, two thirds full of water, and D, the small boiler, quite full. Then screw in the said pipes again as fast and as tight as possible. Then light the fire at b; and when the water in L boils, the handle of the regulator, marked z, must be thrust from you as far as it will go: which makes all the steam rising from the water in L pass with irresistible force through o into P, pushing out all the air before it, through the clack r, making a noise as it goes; and when all is gone out, the bottom of the vessel p will be very hot. Then pull the handle of the regulator to you, by which means you stop o, and force your steam through oo into rp, until that vessel has discharged its air through the clack R up the force-pipe s. In the mean time, by the steam's condensing in the vessel P, a vacuum or emptiness is created, so that the water must and will necessarily rise up through the sucking-pipe T, lifting up the clack M, and filling the vessel P.

"In the mean time, the vessel rp being emptied of its air, turn the handle of the regulator from you again, and the force is upon the surface of the water in p; which surface being only heated by the steam, it does not condense it, but the steam gravitates or presses with an elastic quality like air, still increasing its elasticity or spring till it counterpoises, or rather exceeds, the weight of the water ascending in

s, the forcing-pipe, out of which the water in it will be immediately discharged when once gotten to the top, which takes up some time to recover that power; which having once got, and being in work, it is easy for any 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 far as the steam continues within the vessel, so far is the vessel dry without, and so very hot, as scarce 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 vanishes 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 R, will rattle the clack, so as to give sufficient notice to pull the handle of the regulator to you, which, at the same time, begins to force out the water from Pp, without the least alteration of the stream; only sometimes the stream of water will be somewhat stronger than before, if you pull the handle of the regulator before any considerable quantity of steam be gone up the clack R but it is much better to let none of the steam go off (for that is but losing so much strength), and is easily prevented by pulling the regulator some little time before the vessel forcing is quite emptied. This being done, immediately turn the cock or pipe y of the cistern x on P, so that the water proceeding from x through Y (which is never open but when turned on P, or Pp, but when between them