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FIRE-WHEEL.

131 (numbered 1) into the chamber, a, of the inner series, presses upon the water which it contains, and as the construction of the valves allows it to flow only in one direction, it is forced upwards into the divisions on that side of the wheel nearest the furnace; this gives it a preponderance, and it descends. The cell, a, is now in the position at first occupied by b, and c is in that where it begins to enter the cistern ; the air which is contained in the divisions which had been heated now being brought into contact with the water, it is condensed, and continues so, until, by the revolution of the wheel, it is again brought, in its turn, into contact with the fire of the furnace.

Nothing can be simpler than the hypothetical action of this mechanism ; its effect was, as usual, not underrated. The wheel was twelve feet in diameter, and the cells were calculated to contain 750 cubic feet of water, and an entire revolution to be made in about thirty-five seconds. This great weight, applied tangentially to one side of the wheel, was to give it a continuous preponderance, which was calculated, very minutely, to equal in effect the power of nearly thirty-four horses, or two hundred and thirty-four men.

Throwing the practical merit of this mechanism totally out of the question, the combination is exceedingly meritorious; and considering the time of its invention, and the perfect novelty of the idea, it has many claims to a more favourable consideration as a first thought, than has usually been awarded to it. That it presents glaring defects cannot be denied ; but had length of years been allotted by Providence to its amiable projector, the same ingenuity which first traced the outline might have effectively supplied its deficiencies. A negative proof of its merit is, that it has been

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the type of several attempts at the construction of steam-wheels among later mechanics. Daslesme, his contemporary, fell prodigiously behind him in his idea for raising water by steam; the model, it is said, acted in a manner similar to Decaus's. A notice of it is here introduced, from a wish not to omit the labours of any who, at a time when the subject was little regarded, thought it worthy of their observation and attention.

While Amontons, in France, was engaged in his steam-wheel, and Savery, in England, had achieved so brilliant a triumph, Papin was again exerting himself at Marpurg, in Germany, to bend the same powerful agent to the use of man ; "as if the three nations of Europe, which had made,” says Belidor, “ the greatest advances in science, were each anxious to furnish a learned inan to participate in the glory of so fine a discovery.”

In considering the circumstances under which Papin carried on his researches, it is extraordinary that he should have stumbled, as it were, on 80 admirable a modification as that described by him in 1695, and abandon it almost at the moment when he had in his grasp a brilliant reward for his life of labour. But we learn from the taunts of his rivals, as well as his own confession, that his sanguine hopes and laborious perseverance ended only in pointing out one or two properties of an agent, whose peculiarities foiled all his boasted ingenuity to bend its agency to strictly practical purposes. At the period (1698) of discontinuing his researches he had made considerable progress in an experimental machine; but the frosis of the following November damaging the apparatus, by destroying the valves which were placed in the

ELECTOR OF HESSE.

133

river, was an accident which so discouraged Papin, that the further prosecution of this experiment yielded to matters of less importance, and the machine itself was completely forgotten.*

Few philosophers in his time had such rare facilities of performing experiments, or more ample means to carry his ideas into practice, or more gratifying attention to incite him to perseverance. The Elector of Hesse, under whose patronage he resided in Germany, inheriting that love of science, which, for generations, gloriously distinguished his ancestors, not only furnished the means, but condescended to become his associate in the labour of experimenting.

This enviable position had made his operations to be regarded with great interest by a large circle of men of science, with whom he maintained a liberal and friendly intercourse. The celebrated Leibnitz was numbered among the correspondents of the philosopher of Marpurg; and to him, among others, Papin explained his objects, described his experiment, and related his failure. The ingenuity of the mathematician, however, elicited no device by which his friend could be assisted; but his reply informs us, that years before the period at which he was writing, (June, 1698,) the expansion of steam had presented itself to his mind as a source from whence might be derived a cheap mechanic power.

Thirty years of experiment not having conducted to any useful discovery, offered to Papin no inducement longer to tread a path apparently so harren. But the indifference produced by his own want of success was destined to be stimu.

* Nouvelle manière pour lever l'eau par la force du feu. Mise en lumière par M. D. Papin, Dr. en Méd. Prof. en Mathém. à Marbourg, p. 3. A Cassel, 1707.

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lated by the better fortune attending the labours of another. And the great fame which Savery had acquired in England again roused the ambitious industry of Papin to forget former failures. in the pursuit of new distinction.

The rival of the illustrious Newton, during one of his visits to England, had seen the machine for raising water by fire in action. The experiment of his Marpurg correspondent was then recalled to his recollection ; and at his return to Germany, Leibnitz sent a copy of the “Miner's Friend” to Papin, to have his opinion on its merit.

It may be observed, that Savery's engine, which was figured and described in the “ Philosophical Transactions for 1698," does not appear to have excited Papin's attention as a project. It presented so many difficulties to be surmounted, that Papin, after his own experiments, might be pardoned forming the opinion that Savery's scheme would prove abortive.

But the testimony of Leibnitz, after an inspection of the apparatus, set conjecture at rest. His letter, and Savery's treatise, being submitted to the elector, the subject of the neglected model was resumed, and the prince again became the colleague of the philosopher in the labour of experimenting. The result was the production of a machine, which Papin ascribes to the ingenuity of his royal patron; in the description of his apparatus he claims no other merit for bimself, but that of an experienced assistant and a grateful narrator.

At first view, it bears a strong resemblance to Savery's engine; but on a more careful inspection, it will be found to vary in almost every essential point. It may also be added, it differs prodigiously from the English mechanism in its practical value.

HESSIAN ENGINB,

185 The engraving marked Hesse contains a view of the exterior appearance of the elector's engine ; and the figure beneath it is a section of the same apparatus : a is the boiler, having a pipe, b, closed by a lever valve, through which it is sup. plied with water; the pipe, d, connects it with the forcing vessel, f; z is an iron cylinder, laying in a cavity made in a hollow floater, and which may be inserted through the orifice, g, made in the top of the forcing vessel, and closed by a valve, g, kept in its position by a weight, u, hung on the end of a lever ; &, a funnel through which water is introduced, and closed by a cock, h; the pipe, k, is a continuation of the forcing vessel, S, and is inserted in the reservoir and air vessel, m; 0, a pipe conducting the water, which has been forced into the air vessel, to its destination.

The steam from the boiler, a, flowing through the pipe, d, presses the floating piston downwards, and the water beneath it is thus forced up the pipe, k, into the forcing vessel, m; when the floating piston, *, has reached the limit of its movement, the cock, d, is turned to shut off the further flow of steam into the forcing vessel, and the vapour is allowed to escape from f, by the cock, e; at the same moment, the valve, h, is turned, which allows the water in x to flow into f, and raise up the piston; the water in k being prevented from descending by the valve placed near its bottom. The opening in the lid of the forcing vessel, closed by the lever valve, g, u, is for the purpose of allowing a red-hot iron cylinder to be inserted in order to increase the heat of the steam ; by the water being forced into the receiving vessel, m, the air which it contains is com pressed or condensed, and this is to give a greater velocity to the issuing water. This vessel was

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