Amontons' Air Engine

At this period the exertions of mechanics in France to derive a power from the action of heat, discovered the usual refined ingenuity of that accomplished people; but the results of their labours are considered to have been, on the whole, unsuccessful, inasmuch as they wanted the merit of fitness for practice, which was possessed in so eminent a degree by the machine produced among their insular rivals.

The inventor of a steamwheel is found in the ranks of its most distinguished and industrious philosophers. Guillaume Amontons, the son of a Norman advocate, who settled at Paris, was afflicted, from child hood, with so great a deafness as nearly to deprive him of the society and conversation of mankind.

He began the study of machines for his amusement, and his first essay was an attempt to construct an apparatus to produce a perpetual motion; a perseverance in this research taught him, that he had lost the time he had expended on it, and thrown away his care.
The family of Amontons was opposed to these studies from their beginning, as leading neither to distinction nor to fortune ; but the student despairing, after the failure of a course of medical and surgical experiments, of ever obtaining his hearing, redoubled his attention to mathematical and mechanical pursuits. He designed buildings with taste, and in works of carpentry introduced some theoretical refinements to improve its practice; he invented an ingenious telegraph for conveying a message from Rome to Paris in three or four hours, and the experiment was tried with success in the suburbs of Paris.

His works on hygrometers and barometers are of great merit ; and his theory and experiments on friction are still appealed to for their ingenuity as well as accuracy : for his invention of the "moulin à feu" (or a fire mill), he ranks as an early improver of the steam-engine.

But the amiable qualities of his mind exceeded even the ingenuity of his spirit. Amontons was proverbial for the frankness, and simplicity, and polish of his manners, and for the almost infantine benevolence of his disposition.

The scheme of Amontons, totally different from the idea of Savery, and unique of its kind, thus early attracted the attention of mechanics to supply a desideratum of a continuous rotary motion
from the elasticity of steam. The machine was called, by its inventor, a fire-wheel, and described as operating by the action of heated air, forcing a quantity of water up one side of a wheel and producing a rotary motion by its differing weight from the other side.

Like some of his contemporaries, Amontons appears partial to the expansion of air, and to have forced it into his service in the construction of his engine. Upon the authority of his own drawing it would appear, that the presence of air in his apparatus was more to be avoided than introduced, and that, in fact, all its effective power would be derived from steam. A cursory inspection of his "moulin à feu" will show us, that the water in the inner range of chambers would soon become intensely heated and form vapour, which could not, by any mechanism he has shown, be prevented from filling what may be designated the air-chambers.

The fire-wheel, as described by its author, consists of two concentric ungulas or rings, connected and communicating by means of small pipes 1, 2, 3, 4. The outer ring of the wheel is divided into a certain number of compartments a, b, c, d, e, f. Amoutons describes his as having twelve, and perfectly closed, so as to have no connection with each other. The inner ring is divided into the same number of compartments, marked a, b, c, d, e, f ; each of these communicates with the adjoining chamber by a valve made in each compartment moving on a hinge, and only opening in one direction, and that upwards. Although the two rings and their series of compartments are placed at a distance, each compartment of the one communicates with a corresponding division of the other by small pipes 1, 2, 3, 4. The wheel is placed so as to have one side of its periphery exposed to the action of a fire, and the other side is immersed in a cistern, y, of cold water. Four or five of the lower chambers of the inner series are filled with water.

A fire is then, says Amontons, to be made in the furnace: this will heat the air in the chamber (for example, marked a) of the outer series, which is exposed to its influence, and the air which it contains is rarefied, and flowing through the pipe (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 6, 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 the type of several attempts at the construction of steam-wheels among later mechanics. Dalesme, 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.