A slight examination of the principle upon which this simple apparatus is constructed, will shew that no very considerable force could have been obtained; as the steam passing through the atmosphere in its passage to the wheel, must, to a certain extent at least, be converted into water.
After the publication of the work by Brancas, more than thirty years elapsed ere the publication of the Marquis's "Century" recalled the attention of the scientific world to this important subject; and this invention, which he states as having been completely carried into effect, was evidently very different from that of his predecessors.
It is said that the Marquis, while confined in the Tower of London, was preparing some food in his apartment, and the cover of the vessel, having been closely fitted, was, by the expansion of the steam, suddenly forced off and driven up the chimney. This circumstance attracting his attention, led him to a train of thought, which terminated in the completion of his "water-commanding engine."[9] Of the Marquis's invention no record has been preserved beyond the articles to which we have already alluded in the present work: and in the absence of other data, the Editor readily introduces Professor Millington's design for an engine on similar principles; and which, with a few alterations, might be made available for the purposes recommended by our author.
In this diagram, q represents a strong and close vessel or boiler to contain water, set in brick work like a common copper, with a fire-place r underneath it, having a chimney s. The boiler thus constructed, is intended to afford the means of producing steam: and if we conceive two casks or strong hollow vessels of any form to be placed under the surface of the water, near the boiler, as at t and v, and that each of these vessels has a valve opening into it in its lower part as u u, and two pipes w w, proceeding from the upper part of the vessels to the top of the steam boiler q, while two other pipes x x proceed from the lower parts of these vessels into a cistern y, forty feet above the level of the water; an apparatus thus constructed will nearly form the water-commanding engine, for if the vessels t and v are both filled with water by the valves u u, and the cock z be opened after the steam has accumulated in the boiler, the elastic fluid thus generated will instantly rush down into the vessel t, and when the surface of the water is heated expel the whole of its contents up the pipe a x, into the cistern y, where it will be retained by a valve opening upwards in any part of that pipe, as at a. This done, the cock z must be shut, and after permitting the steam to accumulate for a short time, that at b must be opened, and the steam will rush into the vessel v and perform a similar office, c being the valve to prevent the return of the water. When the steam is shut off from the vessel t, the elastic fluid which had previously been introduced to expel the water, will be condensed by the cold media round it, and thus a vacuum will be produced in the vessel t, consequently a part of the water in which it is immersed will rush into it by the valve u, and occupy the whole internal cavity, thus putting it in a state of preparation for a second opening of the cock z, by which its contents will be again discharged into the cistern y, and so of the two vessels alternately; for while v is emptying, t will be filling, and vice versâ, which agrees with the Marquis's account when he says, "that the man is but to turn two cocks, that one vessel of water being consumed, another begins to force," &c.
The above suggestion for an engine capable of raising water may be still further improved by adding a suction pipe to the valves u u, and the pressure of the atmosphere will increase the working power of the engine more than thirty feet: and should a less height be required, the forcing pipe may be shortened in a proportionate degree: indeed this fact was attended to by the next person who claims the honour of having invented the steam-engine, to which it may now be adviseable to direct the reader's attention.
The engine suggested by Savery for the purpose of raising water, consisted of a boiler a furnished with a safety valve v. The steam-vessel r was connected with the well H, by a suction pipe n; and when water was to be raised the vessel r was filled with steam, which rushing in, soon expelled the air: when that was completely effected, the communication with the boiler was closed, and the steam condensed, which diminishing its bulk, formed a vacuous space within the vessel; the pressure of atmosphere then operating upon the surface of the water in the well, drove it up the pipe. In this form of the apparatus, the inventor was seldom able to raise water more than thirty feet: and when a greater altitude was required, it was effected by the impellent force of high pressure steam. This was accomplished by the ascending pipe k, which was sometimes carried sixty feet higher than the steam-vessel s; and a reference to the great expansive force of steam will show that this operation must be attended with considerable danger. After condensing the steam and filling the vessel r with water, a new supply of steam was then introduced, which pressing on the surface of the water, drove it up the pipe k; and it will be evident that the pressure on the internal surface of the boiler must be proportioned to the height of the column of water thus raised by the steam.