Simple Rotary Emision Engines
Whether the aeolipile shown in the preceding forms, or in any other which is assumed in after times, was employed by the ancients for any practically useful purpose, cannot now be determined; but it is plain, that by attaching mechanism to the axis of the revolving sphere, some application might have been made of this machine. The principle has been repeatedly revived and employed by modern inventors, in what are called rotary engines of simple emission.
It is even seen in the construction of rockets and fire-wheels; and in all cases, where water, fire, steam or gas are generated in a close vessel, and then permitted to issue with violence, it drives the vessel from which it issues, in the opposite direction. The same principle is manifest in the recoil of a gun when fired, and in the simple emission of a fluid from a reservoir.
Hence, if an apparatus be so arranged that water, steam, air, or gas be made to rush out of a close chamber through the arms of a revolving wheel, the apertures through which it escapes being properly directed, the recoil will cause the wheel to revolve, and the machine will constitute a rotary engine of simple emission.
If, instead of employing the principle of recoil, the force of steam issuing from a fixed vessel, as seen in the the case of a spout of a common tea-kettle, be directed on the vanes of a wheel so as to drive it round, this will form another species of rotary steam engine with simple emission.
The theory of such machines, in a variety of different forms, has been carefully investigated, and it has been found that in the most favorable circumstances, not more than half the power of the steam of the best rotary engines, can be made available for any useful mechanical effect.
The celebrated Smeaton and others have subjected their operation to careful experiment, and the results obtained by the experimenters, are stated to be 3 parts out of 11, 8 out of 27, or 2 out of 5, as the greatest useful effect that could be obtained in actual practice.
As patents have sometimes been taken out for air-engines in this country, it may be woth while to make a few remarks on one of those described by Heo, in his work above mentioned. The apparatus may be called a religious pantomime, got up for the amusement and deception of the common people. A fire was kndled upon an altar to the gods, and animated figures were made to lead a choral dance in the interior of the altar, which was rendered visible by some tranparent substance. Through the hearth, a tube was extended to the base of the altar, where it was revolved on an iron pin, the other end being passed through a tubular fitting attached to the hearth.
The tube had other cross tubes attached to it, and communicating with it, so as to radiate opposite to one another, and to have their ends turned in opposite directions. A drum was also attached to the tube, upon which the dancing figures were placed. The air, being heated by the action of the fire, proceeded into the upright tube, and, being forced out through the radiating bet tubes, occaisioned the former, with it's drum, to revolve, and produce the desired effect.
Such an air-engine was only a philosophical toy, and never could produce any useful mechanical effect, owing to the want of force in the moving power. The same may be said of all air-engines, whatever may be the nature of their construction. They seem to act perfectly well in models built on a small scale and of light materials; but whenever they are tried on a large scale, and of a construction intended for practical purposes, they invariably fail, for want of actual ppower in the agent. Seeing, indeed, that common air, and all gases, expand only in the ratio of 8 to 11, when heated from the freezing to the boiling point, how is it possible that any air-engine can be effective when tried on a scale of sufficient magnitude to be a prime mover of machinery?