Again, with steam at 150 lb. pressure above the atmosphere, a generator of the same efficiency would consume only 22.2 lb. of steam per electrical horse power per hour. The results so far actually obtained are a consumption of 52 lb. per hour of steam for each electrical horse power with a steam pressure of 90 lb. above the atmosphere.--_Engineering._ * * * * * HARGREAVES' THERMO-MOTOR. From the researches and investigations of Carnot, Joule, Rankine, Clausius, and Sir William Thomson, the science of thermo-dynamics has not only been brought into existence, but fully matured. We learn from it that whereas in the steam engine, on account of the limited range of temperature in the working cylinder and the rapid conduction of steam during condensation, no combination of cylinders can materially affect its present efficiency, internally fired engines, such as gas and caloric engines--being, as it were, less fettered--can have their already high efficiency increased by simply overcoming mechanical difficulties. To this fact is no doubt due the recent remarkable development of gas and caloric engines. The first caloric or hot air engine was invented by Sir George Cayley in 1807, and in 1827 Dr. Robert Stirling, a Scotch minister, took out his first patent for a hot air engine, which was the foundation of many subsequent machines, and by the invention of the regenerator he converted what was practically a scientific toy into an efficient machine. One of the most ardent workers in this field at the present time is Mr. James Hargreaves, of Widnes, who, with a thorough theoretical knowledge of the subject has, after many years of patient perseverance, over come many of the mechanical difficulties, and designed the engine of which the above is an illustration. The sectional elevation, shown in Fig. 1, is an expanded view of the machine, shown thus to enable the action of the machine to be more clearly understood; the relative position of the different parts, as actually made, is shown in the side elevation (Fig. 4). The principal working parts of the machine are the combustion chamber, D, which is of the form shown, lined with fire brick, and having an entrance, with the door screwed down like a manhole lid; the working cylinder, A, surrounded by the water casing, K; the piston, B, with a water lining, and coupled to the end of the working beam by a parallel motion, the beam being supported by two rocking columns, Z, as in engines of the "grasshopper" type; the air compressor, C, coupled directly to the piston of the working cylinder; the injection pump, F, for supplying the fuel--creosote or coal tar--to the combustion chamber; the regenerator E; the receiver and separator, V Y; the feed and exhaust valves, M. [Illustration: Fig. 1--SECTIONAL ELEVATION--HARGREAVES' THERMO-MOTOR.] [Illustration: Fig. 2.]