Among the numerous patents taken out in consequence of this reaction, the most important, filed in 1860 by M. Hugon, related to a gas motor with a flame ignition, and in which the cylinder was cooled by injecting into it a very fine spray of cold water. Experiments were made upon it in 1876 by M. Tresca, and it was found that the motor consumed 2445 litres of gas per horse-power hour. The temperature of the exhaust gases was 180° C., while in the Lenoir motor they were about 280° C. The diminution in temperature was probably due to the better method of cooling the cylinder, and was found to be a great improvement, the cylinder requiring much less lubrication. In 1861 Kinder and Kinsey somewhat modified the existing arrangements of the parts, but otherwise their motor embodied no new ideas. Another motor was devised about this time by Millon, once more bringing forward Lebon’s idea of compressing the gases in the cylinder itself. We have now reached the year 1862, which may be considered a memorable one in the history of the gas engine, for it was in this year that a patent was taken out by M. Beau de Rochas, setting forth from a theoretical point of view the best working conditions for a gas engine. During the forward stroke of the piston the explosive mixture was to be drawn into the cylinder, during the return stroke this volume of gas being compressed; at the dead point at the beginning of the second forward stroke the explosion was to take place, driving the piston forward, the gases being expelled during the second return stroke. The whole principle will be seen to consist of four distinct operations, forming what is known as the Otto cycle, for reasons which we will presently explain. The peculiar part of the patent was its purely theoretical explanation. Whilst giving all the honour due to the inventor, and recognizing that he fully understood what he was talking about, we must not forget that there was nothing whatever in the patent indicating how the ideas embodied therein might be carried into practice. No drawings were appended to the text, explaining how the gases were to be ignited, or how the exhausted gases were to escape; it contained nothing, in fact, but the plain statement of the most efficient cycle of operations. M. de Rochas did not construct a machine on this principle, and as he omitted to pay his patent fee for the second year, the idea became public property. For these reasons no attention was drawn to it until ten years afterwards, when it came to light during some patent litigation undertaken by Dr. Otto in 1878.