68 THE POPULAR SCIENCE MONTHLY. 



ferentiation ; " the number of parts lias 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 ob- 

 taining 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 resume, working between the widest attainable limits of tempera- 

 ture, and the saving of heat previously wasted in the apparatus or re- 

 jected 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, con- 

 tributes 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 transforma- 

 tion 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 ex- 

 pected to continue, in the near future at least, toward higher steam, 

 greater expansion in more than one cylinder, steam -jacketing, super- 

 heating, 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 pass- 

 ing 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 ex- 

 penditure 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 mate- 

 rial, 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 



