Hence the attempt made by the French inventor, Du Trembly, about the year 1850, and by other inventors since, to utilize a larger proportion of heat by approaching more closely the lower limit, was in accordance with known scientific principles.
We may summarize the result of our examination of the growth of the steam-engine thus:
First. The process of improvement has been one, primarily, of “differentiation;”[117] 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.
Secondly. 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 portion of the machine. This is illustrated by the two cylinders of the compound engine and by the duplication noticed in the binary engine.
Thirdly. The direction of improvement has been marked by a continual increase of steam-pressure, greater expansion, provision for obtaining dry steam, high piston-speed, careful protection against loss of heat by conduction or radiation, and, in marine engines, by surface condensation.
The direction which improvement seems now to be taking, and the proper direction, as indicated by an examination of the principles of science, as well as by our review of the steps already taken, would seem to be: working between the widest attainable limits of temperature.
Steam must enter the machine at the highest possible temperature, must be protected from waste, and must retain, at the moment before exhaust, the least possible amount of heat. He whose inventive genius, or mechanical skill, contributes to effect either the use of higher steam with safety and without waste, or the reduction of the temperature of discharge, confers a boon upon mankind.
In detail: In the engine, the tendency is, and may probably be expected to continue, in the near future at least, toward higher steam-pressure, greater expansion in more than one cylinder, steam-jacketing, superheating, a careful use of non-conducting protectors against waste, and the adoption of still higher piston-speeds.
In the boiler: more complete combustion without excess of air passing through the furnace, and more thorough absorption of heat from the furnace-gases. The latter will probably be ultimately effected 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, and more careful workmanship, especially in the boiler, and much improvement in forms and proportions of details.