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“ two thousand lbs. to a height of four feet. Moreover, I “ ascertained that one minute's time is sufficient for a mode“rate fire to drive the piston in my tube up to the top; but, " as the fire ought to be proportionate to the size of the “ tubes, large tubes could be heated almost as soon as small “ones: whence it is clear what vast moving powers may be “ obtained by help of this most simple contrivance, and at “ how small a cost. For it is known that the column of air “pressing on a tube whose diameter is a foot, counterbalances

nearly two thousand lbs.; but if the diameter be two feet, “ the weight would be nearly eight thousand lbs.; and that, “ in other dimensions, the pressure increases in like manner “ in the triplicate ratio of the diameters. Hence it follows, " that the fire in a grate whose diameter scarcely exceeds “ two feet, might suffice to raise 8000 lbs. each minute to

a height of 4 feet, if tubes were provided of such a height; “ for a fire might be made in a grate of thin iron, to be

easily moved from one tube to another, and so the same “ fire might continually be preparing that most efficacious vacuum in one tube or another.

“ If any one now will consider the magnitude of the forces “ to be obtained in this way, and the trifling expense at “ which a sufficient quantity of fuel can be procured, he will

certainly admit that this my method is far preferable to the “ use of gunpowder above spoken of, especially as in this way

a perfect vacuum is obtained, and so the inconveniences “ above recounted are avoided.

“ In what manner that power can be applied to draw water or ore from mines, to discharge iron bullets to a great dis“ tance, to propel ships against the wind, and to a multitude of other similar purposes, it would be too long here to “ detail ; but each individual, according to the particular “ occasion, must select the construction of machinery appro

priate to his purpose. Here, however, I will in passing “ remark, how greatly such a power is to be preferred to

common rowers for moving vessels in the sea; for, Ist, the

weight of the common rowers loads the vessel, and retards “ its progress; 2ndly, they require much room, and so are a

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great hindrance in the ship; 3rdly, it is not always possible “ to find the requisite number of men; 4thly and lastly, the

rowers, whether they are toiling on the deep, or resting “ in harbour, must always be supplied with needful food, - whereby the expenses are greatly increased. But my tubes “ would, as has been already observed, have a very small “ weight to retard the ship; would also take up little room ; “ might also be readily prepared in sufficient numbers, if once a manufactory were built and fitted

up pose; and, lastly, no fuel would be consumed for the said “ tubes, excepting at the time of the operation; while in “ harbour they would require no expenditure.

“ But since common oars could not easily be moved by “ such tubes, paddle-wheels would have to be employed, such “as I remember having seen in a machine constructed at “ London by command of the Most Serene Rupert Prince “ Palatine, which was put-in motion by horses, by aid of oars “ of that sort, and which left a long way behind it the Royal s barge manned by sixteen rowers. So, no doubt, oars fixed “ into an axis could be most conveniently driven round by

my tubes, by having the rods of the pistons fitted with “ teeth, which would force round small wheels, toothed in “ like manner, fastened to the axis of the paddles. It would

only be requisite that three or four tubes should be applied “ to the same axis, by which means its motion could be con“ tinued without interruption; for, while any one piston might “ be touching the bottom of its tube, so that it could drive the “ axis round no further, before being again propelled by the “ force of the steam to the top of the tube, the bolt of another “ piston could immediately be removed, the force of which in “ its descent would continue the motion of the axis; and so,

again, yet another piston could be lowered, and exert its “ force on the same axis, while the pistons first pressed down

were again being raised to the top by the force of heat, " and so were gaining new force to move the said axis, in “ the manner above described. But one grate, containing " a moderate fire, would be sufficient to raise all of those “ pistons in succession.

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" Perhaps, however, some one may object, that the teeth of “ the piston-rods, fitting into the teeth of the wheels, must in “ their ascent and descent communicate opposite movements “ to my axis; and that so the ascending pistons would hinder “ the movement of the descending ones, and the descending

pistons would hinder that of the ascending ones. But this

objection is a very trifling one; for machine-makers are “ well acquainted with a method whereby toothed wheels are

so fixed to an axis, that when moved round in one direction

they carry the axis round with them, but when going round “ in the other direction they communicate no movement to the “ same axis, but allow it to be very freely turned round with

an opposite movement. The principal difficulty, therefore, “ consists in finding the manufactory for easily making very

large tubes, as I have more fully stated in the Acta Eruditorum for September, 1688. And for preparing that, this “ new machine ought to supply no small additional induce“ment; inasmuch as it very clearly shows that such very

large tubes can be most advantageously employed for several “important purposes.”

In his “Recueil,' published in 1695, in which Papin has included his Memoir of 1690, he has added to the engraving of which we have given a copy, one of a cylinder with a piston, the upper part of the piston-rod toothed, and the teeth fitting those of a small toothed wheel placed beside it; and, in an addition to the same Memoir, he there suggests making a vacuum in a number of tubes in succession, each to be removed for use as it is emptied, having, he says, found it better to bring the tubes to the fire than the fire to the tubes. On his first system he says it took a minute to form each vacuum; on the new one he could do it in a fourth of that time: and he adds that he now knew of a very good method of casily making large, light, and evenly-formed tubes.

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CHAPTER XII.

TIIOMAS SAVERY THE MINER'S FRIEND DESCRIPTION OF HIS STEAM

ENGINE USES TO WHICH IT COULD BE APPLIED — L'APIN'S INFERIOR IMITATION OF IT - ESTIMATE BY HORSE-POWER SIR SAMUEL MORELAND NEWCOMEN AND CAWLEY THEIR GREAT IMPROVEMENTS DESAGULIERS AMONTONS AND DALESMESMEATON.

In the contrivance which Papin has thus described, the vessel in which the steam was tediously generated, and then allowed slowly to condense, was at once boiler and cylinder; and, so long as it continued to fulfil alternately the functions of both of those vessels, it was necessarily unfit to do any really effective work. In order to the accomplishment of that desideratum, it was essential that the steam should, on the one hand, be steadily, continuously, and abundantly produced, and, on the other, that it should from time to time be condensed with at least tolerable rapidity. The honour of making this great step in advance,—the first that in fact led to the attainment of any really useful results from the employment of steam as a motive power of machinery, and which, therefore, it seems impossible too highly to commend,- belongs entirely to an Englishman, Captain Thomas Savery. Of his life and private history but little appears to be known; and an enquiry made several years ago of a gentleman of the same name at Bristol, (who acknowledged relationship), did not produce any information or papers.

But of his steam-engine Savery has luckily left us a very particular description, in a work entitled The Miner's

a " • Friend, or an Engine to raise Water by Fire described, ' and the Manner of fixing it in Mines, with an Account of

the several other uses it is applicable unto; and an Answer ' to the objections made against it. By Tho. Savery, Gent. * Pigri est ingenii contentum esse his quæ ab aliis inventa sunt. Seneca. London, printed by S. Crouch at the corner of

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Pope's-head Alley in Cornhill. 1702.' The edition from which we copy this title is of that date; but Mr. Robert Stuart, in his . History of the Steam-engine, published in 1824, says, quoting from Robison, “ The fact is, Savery “ obtained his patent in 1698, after a hearing of objec

tions; *** but, besides this, he had erected several of “ his engines before he obtained his patent;" "and,” con

“ ” tinues Mr. Stuart, “ published an account of his engine in “ 1696, under the title of The Miner's Friend, and a Dialogue

by way of answer to the objections which had been made " against it, in 1699; both were printed in one volume in 1702.” We have not seen the publication of 1696; but we observe that in that of 1702, he says he worked a small model before some members of the Royal Society, on the 14th of June, 1699; and also, that, previous to the Royal Assent being obtained to the Patent and Act of Parliament, (i. e. in 1698), he had performed an experiment with a small model of the engine before the King at Hampton Court, to his Majesty's “ seeming satisfaction of the power and use of it.” And he adds, that it is “ now fully compleated, and put in “practice in his dominions, with that repeated success and

applause that it is not to be doubted but that it will be “ of universal benefit and use to all his Majesty's subjects.” What is most important is, that the letter-press of “The • Miner's Friend' is accompanied by a very clear and sufficiently well-executed engraving, including two figures, each of about twelve inches in height, of which the first represents The Engine for raising Water by Fire,” and the second represents the same engine “working in a mine.” In the former, the various parts are all delineated on such a scale, that, with the aid of the particular description accompanying it, it is impossible to mistake either their proportion or their mode of action; and of both figures it may with perfect confidence be asserted, that they are the first representations to be met with in the publications of any country, of a real steam-engine doing useful work.

Savery's engine, as so described and delineated, acted by two distinct principles ; raising water, in the first place, by

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