The accompanying engravings illustrate Edwards' patent gas engine, made by Messrs. Cobham & Co., Stevenage, Herts, recently exhibited at York. In our engravings, a is the foundation plate of the engine, having the bearing, b, in which the crank shaft, c, revolves; d, an inclined plate upon the foundation, a, to which the cylinder, e, and casing, f, are bolted; g is a piston working in the cylinder, e, and having a hollow rod or trunk, h, to which is jointed the connecting rod, i, which drives the crank pin, k. The guide, l, fits upon the hollow trunk, h, and is itself surrounded by the air casing, m, which communicates with the casing, f, through openings, n n, in the inclined plate, d. The guide, l, has openings, o o, through which air enters the casing, m, when the hollow trunk, h, is at the inner end of its stroke; p is the exhaust pipe, and r is a casing round the cylinder, e, through which water may be made to circulate by pipes at s, t. The valve seat, v, fits into the cylinder, e, and has holes, w, for the admission of air, and x for the admission of gas through the central pipe, y. The valve, z, consists of a disk of metal covering these holes and guided by a spindle, A, the outer end of which is fitted with a metal or India-rubber spring at B, and a regulating nut, C. The gas pipe, y, is shown supplied from a flexible bag, D, the supply to which from any convenient source is regulated by a cock or valve at E. The piston, g, contains a disk exhaust valve, G, the spindle, H, of which is fitted with a closing spring, I, and the end of the spindle is pressed down during the inner stroke of the piston by a tail-piece, K, on the inner end of the connecting rod, i. Holes, L, open from the hollow piston above the exhaust valve, G, into the cylinder round the hollow trunk, h, and thence to the exhaust pipe, p. At or near one-third of the stroke of the piston a firing valve, P, is arranged, having an inlet hanging valve of the usual kind, through which a flame burning outside is drawn when the valve is uncovered by the piston, g. The outer end of the casing, f, is closed by a cover, R, to which the valve seat, v, and gas inlet pipe, g, are connected.

The operation of the engine is as follows: The piston, g, being at the inner end of its stroke, the crank is turned round in the direction of the arrow, and the piston draws air in through the holes, w, and gas through the holes, x, the two mixing as they pass under the inlet valve, z. When the piston has advanced far enough to uncover the firing valve, P, the flame is drawn in and the inflammable mixture exploded, the expansion of the air and gas closing the inlet valve, z, and carrying the piston to the end of the stroke. The momentum of the fly-wheel then carries the piston back through its return stroke, during which the tail-piece, K, presses the spindle, H, and opens the exhaust valve, G, through which expanded air and gas escape to the exhaust pipe, p. It is claimed that this arrangement is very effective in securing a complete clearance from the cylinder of the products of combustion, which, when not wholly removed, vitiate the incoming charge and reduce efficiency.

When the piston arrives at the inner end of its stroke, the exhaust valve, G, is closed by the spring, I, and a fresh supply of air and gas are drawn in through the inlet valve seat, v, as the piston again commences its outer stroke. In order to keep the cylinder, e, sufficiently cool, whether the water casing at r, be used or not, the whole supply of air is drawn from the front end of the cylinder through the openings, n n, and thence between the cylinder, e, and the casing, f, and round the end of the latter to the inlet valve, v. And in order to prevent or lessen the noise of the explosions, the hollow trunk, h, is made of such length that its front edge closes the openings in the guide, l, through which air is drawn into the air casing m, and through the openings, n n, just before the explosion takes place, the noise of which therefore cannot escape. For the same purpose fibrous or porous material, such as mineral or slag wool, may be placed loosely in the space between the cylinder and the casing, f.

The engine may be made to revolve in the opposite direction to the arrow by turning the piston and connecting rod round so that the tail-piece upon the latter is above instead of below, and instead of the water casing, r, radial ribs may be formed upon the cylinder, e, from which the air passing between them inside the casing, f, absorbs the heat. The cylinder is arranged preferably in the inclined position shown, but it may, of course, be fixed in any other convenient position.—Engineering.