About this time (1850-60) M. Beau de Rohes, a French engineer, thoroughly investigated the reasons of the uneconomical working of gas motors, and found that it was due to want of sufficient compression of the gas and air previous to explosion, incomplete expansion and loss of heat through the walls of the cylinder, and he was the first to formulate a “cycle” of operations necessary to be followed in order to render a gas engine efficient. They related to the size and dimensions of the cylinder; the maximum speed of the piston; the greatest possible expansion, and the highest pressure obtainable at the beginning of the act of expansion. The study and application of these conditions created great advancements in gas engines. With the discovery and development of the oil wells in the United States about 1860 a new fuel was found in the crude petroleum, as well as a source of light. The application of petroleum to engines, either to produce furnace heat, or as introduced directly into the piston cylinder mixed with inflammable gas to produce flame heat and expansion, has given a wonderful impetus to the utilisation of gas engines. G. H. Brayton of the United States in 1873 invented a very efficient engine in which the vapour of petroleum mixed with air constituted the fuel. Adolf Spiel of Berlin has also recently invented a petroleum engine. Principal among those to whom the world is indebted for the revolution in the construction of gas engines and its establishment as a successful rival to the steam engine is Nicolaus A. Otto of Deutz on the Rhine. In the Lenair and Hugon system the expansive force of the exploded gas was used directly upon the piston, and through this upon the other moving parts. A great noise was produced by these constant explosions. In the Otto system the explosion is used indirectly and only to produce a vacuum below the piston, when atmospheric pressure is used to give the return stroke of the piston and produce the effective work. The Otto engine is noiseless. This is accomplished by his method of mixing and admitting the gases. He employs two different mixtures, one a “feebly explosive mixture,” and the other “a strongly explosive mixture,” used to operate on the piston and thus prolong the explosions.