Page:Popular Science Monthly Volume 13.djvu/78

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ferentiation";" the number of parts has been continually increased, while the work of each part has been simplified, a separate organ being appropriated to each process in the cycle of operations.

2. A kind of secondary process of "differentiation" has, to some extent, followed the completion of the primary one, in which secondary process one operation is conducted partly in one and partly in another part of the machine. This is illustrated by the two cylinders of the compound engine, and by the duplication noticed in the binary vapor-engine.

3. The direction of improvement has been marked by a continual increase of steam-pressure, greater expansion, special provision for obtaining dry steam, higher piston-speed, careful protection against loss of heat by conduction or radiation, and, in marine engines, by surface condensation.

The direction of improvement, as indicated by science as well as by our own review of the actual steps already taken, would seem to be: En résumé, working between the widest attainable limits of temperature, and the saving of heat previously wasted in the apparatus or rejected from it.

Steam must enter the machine at the highest possible temperature, must be protected from waste or loss of heat, and must retain, at the moment before exhaust, the least possible proportion of originally available heat. He whose inventive genius, or mechanical skill, contributes to effect either of these objects—to secure either the use of higher steam with safety, or the more effective conversion of heat into mechanical power without waste, or the reduction, by transformation into work, of the temperature of the rejected working-fluid—confers an inestimable boon upon mankind.

In detail, in the engine proper the tendency is, and may be expected to continue, in the near future at least, toward higher steam, greater expansion in more than one cylinder, steam-jacketing, superheating, a careful use of non-conducting protectors against waste, and higher piston-speed with rapid rotation, and to the adoption of special proportions and of forms of valve-gear adapted to such high-speed engines.

In the boiler, more complete combustion, without excess of air passing through the furnace, is sought, and a more thorough absorption of heat from the furnace-gases. The latter may be ultimately found most satisfactorily attainable by the use of a mechanically-produced draught, in place of the far more wasteful method of obtaining it by the expenditure of heat in the chimney.

In construction, we may anticipate the use of better materials, as already seen in the substitution of "mild steels" for the cruder material, iron, and more careful workmanship, especially in the boiler, and still further improvement in forms and proportions of details.

In management, there is an immense field for improvement, which