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. Summarizing the ground over which we have passed, we find the origin of the gas engine in the minds of the same men as were first to propose the steam engine, Huyghens and Papin, 1680 and 1690. Greater mechanical difficulties and ignorance of the nature of explosives caused the abandonment of the internal combustion idea, and the mechanical difficulties with steam being less, the steam engine became successful, and triumphed over its rival. The knowledge and skill gained in the construction of steam engines made it possible once again to attack the more difficult problem, and simultaneously with the introduction and perfecting of the steam engine, the gas engine idea became more and more possible, the practicable stage commencing with Lenoir and continuing with Hugon, Millein, Otto and Langen, F.H. Wenham, then Otto and Clerk. In 1860, 95 cubic feet of gas produced one horse power for an hour; in 1867, 40 cubic feet accomplished the same thing; and now (1885) we can get one horse power for an hour for from 15 to 20 cubic feet of gas, depending on the size of the engine used. Considered as a heat engine, the gas engine is now twice as efficient as the very best modern steam engine. It is true the fuel used at present is more expensive than coal, and for large powers the steam engine is the best because of this. But the way is clearing to change this. Gas engines as at present, if supplied with producer gas, produced direct from coal without leaving any coke, as is done in the Siemens, the Wilson, and the Dawson producers, will give power at one-half the cost of steam power. They will use 7/8 of a pound of coal per horse power per hour, instead of 1-3/4 lb., as is done in the best steam engines. The only producer that makes gas for gas engines at present is the Dawson, and in it anthracite is used, because of the difficulty of getting rid of the tar coming from the Siemens and Wilson producers, using any ordinary slack.