The motor on the outstroke crosses V-shaped parts about from one-sixth to one-seventh from the out end, the displacer charge now passing into the motor cylinder, displacing the exhaust gases by these ports and filling the cylinder and the space at the end of it with the explosive mixture.  The introduction of some air in advance of the charge serves the double purpose of cooling down the exhaust gases and preventing direct contact of the inflammable mixture with flame which may linger in the cylinder from the previous stroke.  The instroke of the motor compresses the charge into the conical space at the end of the cylinder, and, when fully compressed, ignition is effected by means of the slide I have upon the table.

This system of ignition has been found very reliable, and capable of acting as often as 400 times per minute, which the Otto ignite is quite incapable of doing.  By this cycle the advantages of compression are gained and one step nearer to the steam engine is attained, that is, an impulse is given for every revolution of the engine.

As a consequence, I am able with my engine to give a greater amount of power for a comparatively small weight.  In addition to this, I have introduced a method of self-starting; in this I believe I was the first—­about 100 of my engines are now using self-starting.

The largest single engine I have yet made indicates 30 H.P.  The consumption of gas in Glasgow is:  Clerk engine consumes in Glasgow 18 cubic feet per I.H.P. per hour; Clerk engine consumes in Manchester 22 cubic feet per I.H.P. per hour.  So far as I know, the Otto engine and my own are the only compression engines which have as yet made any success in the market.  Other engines are being continually prepared, gas engine patents being taken out just now at the rate of 60 per annum, but none of them have been able as yet to get beyond the experimental stage.  The reason is simply the great experience necessary to produce these machines, which seem so very simple; but to the inexperienced inventor the subject fairly bristles with pitfalls.

I have here sections of some of the earlier engines, including Dr. Siemens’ and Messrs. Simon and Beechy.  Although interesting and containing many good points, these have not been practically successful.

The Simon engine is an adaptation of the well-known American petroleum motor, the Brayton, the only difference consisting in the use of steam as well as flame.

Dr. Siemens worked for some twenty years on gas engines, but he aimed rather high at first to attain even moderate success.  Had he lived, I doubt not but that he would have succeeded in introducing them for large powers.  In 1882 he informed me that he had in hand a set of gas engines of some hundreds of horse power for use on board ship, to be supplied with gas from one of his gas producers modified to suit the altered conditions.