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DISCOVERIES IN NATURAL PHILOSOPHY.

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first to depend, as well as towards the construction of the apparatus.

Galileo, in 1640-41, surmised the true nature of a vacuum, and of the pressure of the atmosphere. His pupil Torricelli, pursuing the subject after the death of Galileo, invented the barometer, and proved the theory in 1643. Pascal, hearing of it, as he says, at Rouen, published, in 1647, his 'Nouvelles Expériences touchant le Vuide,' confirming the deductions of the Italian philosophers; and he caused to be made, in 1648, the memorable experiment of the Puy de Dôme, thereby establishing the variation in the pressure of the atmosphere at different heights, which Descartes had before conjectured.

Otto de Guericke had in the meantime applied himself to the same subject, and invented an air-pump, the effects of which he exhibited to the assembled German Princes at the Diet of Ratisbon in 1654. An account of this was published by Gaspar Schottus, first in his book 'De Arte Mechanicâ Hydraulicopneumaticâ,' in 1657, to which it forms an appendix; and afterwards, with several additions, as Guericke has informed us, in his 'Technica Curiosa,' Norimb. 1664, 4to. Robert Boyle passed some time at Florence in 1642, in which year Galileo died at a neighbouring village; he published, in 1660, 'New Experiments upon the Spring of Air,' and described therein an air-pump he had invented two or three years before, and which had been improved by Hooke. The experiments of the Accademia del Cimento, which are very full upon this subject, were published at Florence in 1666. Otto Guericke did not himself publish until a later period; for although he states in the preface to his work entitled "Experimenta Nova Magdeburgica de Vacuo Spatio,' that it was completed on the 14th of March, 1663, yet he adds that, partly in consequence of illness, and partly from other occupations, a delay of seven years occurred in placing it before the world. It was at last published at Amsterdam in 1672, and its appearance } then seems to have been in part owing to the exertions of certain

illustrious friends of its author. Looking at chapters 27 and 28

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of book п., and at the iconismi numbered xrv. and xv., where Guericke describes and delineates a cylinder with a packed piston and rod, and states his mode of forming a vacuum, by extracting the air under the piston by means of his air-pump, and thus producing a power for raising weights by the pressure of the atmosphere, we observe a great similarity to the apparatus in which Papin, several years later, when residing at Marburg, formed his vacuum by the condensation of steam.

The notion of the existence of such a thing as a vacuum,which the old doctrine had taught that "Nature abhorred,”—and the right explanation of its true nature; the construction and use of the air-pump; the cylinder with its piston-rod, and piston packed so as to be air-tight although moveable in the cylinder, and with its upper surface exposed, so that the air should act on it as a power, when the close cylinder beneath was exhausted; are all so many distinct steps towards the formation of the atmospheric steam-engine of last century; which, under the hand of Watt, cast off altogether its dependence on the atmosphere, and for the first time became in every sense a true steam-engine; deriving its vacuum from the condensation of steam on one side of the piston, and its power from the impulse of steam on the other, and vice versa, according as the stroke made is downwards, and upwards, in uninterrupted succession.

CHAPTER XI.

DENYS PAPIN-HIS MEMOIR OF 1690—ATTEMPT TO FORM A VACUUM BY GUNPOWDER HIS SUBSEQUENT ADOPTION OF SAVERY'S PRINCIPLE-HIS DIGESTER-MISTAKES OF ENGLISH AND OF FRENCH WRITERS IN REGARD TO HIS INVENTIONS TRANSLATION OF HIS PAPER OF 1690.

We come now to the Memoir in which Denys, or Dionysius Papin, in the year 1690, availing himself of the apparatus of Guericke, and of the true ideas as to a vacuum and the pressure of the atmosphere, of which we have just been speaking, set forth another important fact which he had observed. This was, that if a close cylinder were filled with steam, and the steam were then allowed to condense, a vacuum would be formed within the cylinder; and that, consequently, a moveable piston, fitted to the interior of the cylinder, would then fall, under the pressure of the atmosphere; just as it did in Otto Guericke's experiment, where the vacuum had been formed by the air-pump.

Papin mentions, in the outset of his Memoir, that he had applied steam to that purpose, in consequence of the failure of a previous attempt he had made to obtain a vacuum by the explosion of gunpowder, in the same cylinder, beneath the piston; the explosion always leaving the vacuum imperfect, on account, as he supposed, of a portion of the air which remained, or, as we should now say, of the gases which were the products of the combustion. But he proposed to carry out his ingenious idea of forming the vacuum by condensation, by the clumsy, tedious, and unprofitable expedient of removing the fire from beneath the cylinder, previous to each stroke or descent of the piston.

To practice, Papin seems never to have attempted to apply it,

notwithstanding the suggestions to that effect contained in his Memoir; and we also find that on the appearance of a better invention for condensing the steam, eight years afterwards, Papin abandoned his own scheme, and betook himself to the construction of an engine, (which, however, turned out not to be a good one,) in which he made use of the new plan.

The best methods of applying the power to those various mechanical processes, which both Papin and his great advocate M. Arago have treated as difficulties of a very secondary kind, have in reality proved far otherwise; they have exercised the ingenuity of the most eminent engineers for upwards of a century and a half; and without their solution no mechanical power, however great, could be deemed of very much use to the world.

We reprint at full length a translation of the paper published by Papin in the "Acta Eruditorum Lipsiæ," for 1690, in which we have endeavoured to convey very literally the sense of the original; together with a fac-simile engraving on wood of the figure, with letters of reference, by which the paper in the Leipzig Transactions is accompanied. On this paper, Papin's claims to be considered one of the early inventors of the steam-engine, so eagerly urged by his countrymen, principally depend; and it is, at all events, an interesting record of very considerable ingenuity on his part.

"A NEW METHOD OF OBTAINING VERY GREAT MOVING POWERS AT SMALL COST. BY DENYS PAPYN.

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"In the machine for a new use of gunpowder, which is described in the Acta Eruditorum' for the month of September, 1688, the first desideratum was, that the gunpowder fired in the bottom of the tube A A should fill the whole cavity with flame, so that the air might be entirely expelled from it, and the tube remain a per

* Translated from the "Acta Eruditorum Lipsia" for 1690, pp. 410-414. The paper is also reprinted in the original Latin, in the "Origin and Progress of the Mechanical Inventions of James Watt," 1854, vol. iii. pp. 139-154.

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PAPIN'S MEMOIR OF 1690.

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fect vacuum beneath the piston B B. But there it was mentioned that the desired effect could not be sufficiently attained; but that, notwithstanding all the precautions there specified, there always remained in the tube about a fifth part of the air usually contained in it. Whence a two-fold inconvenience arises: viz. 1st, that in this way we lose half of the desired effect, so that scarcely can 150 lbs. weight be raised to the height of one foot, when otherwise 300 lbs. ought to have been raised, if the tube A A had been perfectly emptied; and 2ndly, that as the piston gradually descends, the force which makes it descend is itself diminished, as was also observed in the passage already referred to. Thus we have to provide, by some contrivance, that, as the moving force decreases, the resistance may in like manner decrease, so that it may be overcome by the aforesaid moving force until the end: just as in watches the unequal force of the main-spring, which moves the whole machine, is so regulated by art, that through the whole of its running down it overcomes the resistance of the wheels with equal ease. But it would be far more convenient if the moving force were to remain always the same, from the beginning to the end. Some attempts have, therefore, already been made to ascertain how a perfect vacuum could be obtained by the help of gunpowder; for in this way, were there no air to offer resistance beneath the piston, the whole column of the atmosphere pressing upon the said piston would press it with an equable force down to the bottom. But hitherto such attempts have been in vain, and always, after the flame of the gunpowder is extinguished, about a fifth part of the air remains in the tube A A.

66 'By another way, therefore, I endeavoured to attain the same end; and, since it is a property of water that a small quantity of it, converted into steam by the force of heat, has an elastic force like that of the air, but, when cold supervenes, is again resolved into water, so that no trace of the said elastic force remains; I felt confident that machines might be constructed, wherein water, by means of no very intense heat, and at small cost, might produce that perfect vacuum which had failed to be obtained by aid

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