generating and destroying, at pleasure, an atmospheric pressure in a metal cylinder.

This problem Papin has solved. His grand and beautiful solution consists in substituting an atmosphere of steam for the atmosphere of common air; in replacing this latter by this latter by a gas which, at 100° centigrade, has precisely the same elastic force, but which has, in addition, this important advantage, which is not possessed by the ordinary atmosphere, viz. that the force of the aqueous gas very rapidly diminishes when the temperature is lowered, and that it even ends at last by disappearing almost entirely, if the cooling down has been carried far enough.* I might very well and more shortly

* The claims of Denys Papin to the invention of creating a vacuum by the condensation of steam, are stated by M. Arago in the Annuaire for 1830, to have been recorded by Papin himself in a Memoir in the Acta Eruditorum Lipsiæ for 1690; and again in a Collection of his works on machines, printed at Cassel in 1695. Belidor gives him the priority in his " Architecture Hydraulique," tome ii. p. 308, printed in 1739; but his claims appear to have been nearly forgotten when they were urged by the eminent French mathematician Bossut, in his "Hydrodynamique,” of which the first edition was published in 1771, and the second in 1796. They were disputed by Dr. Robison in his article STEAM ENGINES, in the Encyc. Brit. in 1811, probably taking Belidor as his authority, who, in the page above referred to, quotes for the origin of the invention, a work of Papin's entitled "Nouvelle maniere d'elever l'eau par la force du feu," printed at Cassel in 1707. We have no doubt that Dr. Robison, relying on Belidor, pushed his enquiries no further.

This, however, was set right by Stuart and by Farey, in their respective Histories of the Steam-Engine, published in 1824 and 1827. But Papin's most able advocate has been M. Arago, who entered into the detail of his publications and schemes in the Annuaire for 1830. We greatly wish that that gentleman, or some other learned countryman of Papin, would give to the world a

characterise Papin's discovery, by saying that his collected edition of all his works. We have not had an opportunity of referring to the greater part of them.

The few years which preceded Papin, about the middle of the seventeenth century, form a most brilliant era in the history of discoveries in natural philosophy.

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 his death, invented the barometer, and proved the theory in 1643. Pascal hearing of it, as he says, at Rouen, published, in 1647, his "Nouvelles Experiences 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 Dome, thereby establishing the variation in the pressure of the atmosphere at different heights, which Descartes had before conjectured :—" Ce qui nous ravit tous," says M. Perier, who, at Pascal's request, made the experiment-in speaking of the phenomenon observed in it, "d'admiration et d'étonnement." He further developed the theory, in 1653, by many experiments, which were not published until 1663, a year subsequent to his death, in his "Traitez de l'Equilibre des Liqueurs et de la Pesanteur de la Masse de l'Air."

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, the account of which was published by Gaspar Schottus, 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 Academia 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. His work entitled "Experimenta nova Magdeburgica de vacuo spatio, &c." Amst. 1672, is now before us, and looking to his chapters 27 and 28 of lib. 11., and his Iconismi xiv. xv. where he 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. In

object was to employ steam for producing a vacuum

deed, we think it pretty apparent, that the Professor of Marburg not only borrowed the apparatus, but took the novel idea of using the pressure of the atmosphere as a power, from the far-famed burgomaster of Magdeburg. Germany thus claims a share in the invention of THE great machine, as it is called, by just anticipation, in the correspondence between the Marchioness of Worcester and her confessor.

Belidor, quoting from the work of Papin in 1707, says that “from the year 1698, he had made a number of experiments by desire of the Landgrave Charles of Hesse Cassel, to raise water by fire, which he had communicated to divers persons, and among others, to Leibnitz, who answered that he also had entertained the same idea.

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"This work having been interrupted," continues Papin, “ would perhaps have been forgotten, had not Leibnitz, in a letter of 6th January 1705, done me the honour to ask my opinion of the machine of Mr. Thomas Savery, of which he sent me the print made in London. Although its construction was a little different from ours, and I had not the description sent me, I saw at once that the English machine and that of Cassel were founded upon the same principle, as I shewed to the Landgrave; which caused his Highness to resume the design of pushing on this invention, which, without doubt, is a very useful one, as will be seen hereafter. I can then testify, that it has cost much time, labour, and expense, to bring it to its present state of perfection. It would be tedious to particularise all the unforeseen difficulties met with, and all the trials which have turned out contrary to expectation; and, therefore, I shall limit myself to making known how far what we now have, is preferable to what we had done at first, and to what Mr. Savery has since done, that the public may not be under any mistake in the choice of these different machines, and may profit, without trouble, by what has proved so expensive; and likewise, that they may see that their obligation to his Highness is not solely for having formed the first plan, but for having overcome the difficulties of the first execution, and brought matters to their present state of perfection.”

Belidor, after this long quotation, goes on to observe―" M. Papin then gives the description of the machine he had executed, and forgets nothing to give it value. But whatever he may say, it is very far from being equally ingenious and complete with that of Mr. Savery, which possesses the advantage of having within itself all the movements it requires, without any one touching it; whereas, the other cannot act without the help of several men, one of whom at least is

in a great space, and that this method is, besides, both expeditious and economical.*

The machine in which our illustrious countryman was thus the first to combine the elastic force of steam with the property which it possesses of being annihilated when it is cooled down, he never constructed on a great scale. His experiments were always made upon mere models. The water from which the steam was to be supplied, did not even occupy a separate boiler; contained in the cylinder, it rested on the metallic plate which closed its lower extremity. It was this plate which Papin heated directly, to convert the water into steam; it was from the same plate that he removed the fire, when he wished to effect the condensation. Such a process, scarcely tolerable in an experiment intended to verify the accuracy of a principle, would evidently be out of the question if it were necessary to make the piston move with

required to give his work uninterruptedly, with contrivances which render this machine as imperfect as that of Mr. Savery is complete." It does not, in fact, appear that the engine improved by Papin, after he was made acquainted with Savery's engine, was ever brought into practical use. Tr.

* An English engineer, deceived, no doubt, by some inaccurate translation, lately pretended that the notion of employing steam in the same engine, both as an elastic force and as a means of rapidly producing a vacuum, originated with Hero. But I, for my part, have indisputably proved that the Alexandrian mechanician never even thought about the steam; that in his apparatus the alternate movement was to be produced solely by the expansion and condensation of air, arising from the intermittent action of the rays of the sun.-M. ARAGO.

It is here to be observed, that Hero's apparatus spoken of by M. Arago in the above note, is not the æolipile mentioned at p. 23. There, steam is the power, and the motion is continuous.—TR.

rapidity. Papin, whilst he says that the end may be attained "by various constructions, which may be easily imagined," points out none of those various constructions. He leaves to those who came after him, the merit both of the application of his fertile idea, and of the invention of those subordinate parts which alone can ensure the success of an engine.

In my earlier enquiries into the use of steam, I have had occasion to mention ancient philosophers of Greece and Rome; one of the most renowned mechanicians of the school of Alexandria; a Pope; a gentleman of the Court of Henry IV.; a hydraulist, a native of Normandy,—that province so fruitful in great men, and which has enriched the national Pleiades with a Malherbe, a Corneille, a Poussin, a Fontenelle, a Laplace, a Fresnel;-a member of the House of Lords; an English engineer; and finally, a French physician, member of the Royal Society of London. For the truth must out, that Papin, an exile for nearly the whole of his life, was only a correspondent of our Academy. But now, plain artisans, plain workmen, are about to enter the lists. Thus all ranks of society will be found to have united in creating an engine by which the whole world was to benefit.

In 1705, fifteen years after the publication of Papin's first memoir in the Leipzig Transactions, Newcomen and Cawley, the one an ironmonger, the other a glazier at Dartmouth in Devonshire, constructed,―(observe particularly that I do not say devised, for there is a wide difference,)—con