THE GROWTH OF THE STEAM-ENGINE. 65 



the combustion of fuel, into mechanical power, using steam as the re- 

 ceiver and conveyer of that heat. 



The problem embodies two distinct and equally important inquiries: 

 The first, What are the scientific principles involved in the problem, as 

 stated? The second, Sow shall we construct a machine that shall 

 most efficiently embody and accord with not only knoicn scientific prin- 

 ciples, but also with all well-settled principles of engineering practice? 



The one question is addressed to the man of science ; the other to 

 the engineer. They can only be satisfactorily answered, even so far as 

 our knowledge at present permits, after studying with care the scien- 

 tific principles involved in the theory of the steam-engine, under the 

 best light that science can afford us, and by a careful study of the vari- 

 ous steps of improvement that have already taken place, and of accom- 

 panying variations of structure, analyzing the effect of each change 

 and tracing the reasons therefor. The theory of the steam-engine is too 

 important and too extensive a subject to be treated in even the space 

 available for a complete course of college lectures ; and we can only 

 here attempt an exceedingly concise statement of the principles, pointed 

 out by science, as those applicable in the endeavor to increase the eco- 

 nomic efficiency of the steam-engine. 



The teachings of science indicate that, in the modern steam-engine : 

 Success in economically deriving mechanical power from the energy 

 of heat-motion will be the greater as we work between more 'widely- 

 separated limits of temperature, and as we more perfectly provide 

 against losses by dissipation of heat in directions in which it is tin- 

 available for the production of power. 



Scientific research has proved that, in all varieties of heat-engines, a 

 very great loss of effect is unavoidable from the fact that we cannot 

 reduce the lower limit of temperature, in working, below a point that 

 is far above the absolute zero of temperature : the point corresponding 

 to the mean temperature of the surface of the earth in our latitude is 

 now practically our lower mean limit of temperature. The higher the 

 temperature of the steam, however, when it enters the engine, and the 

 lower the temperature at which it leaves the cylinder, and the more 

 thoroughly we provide against waste of heat by conduction and radia- 

 tion, and of power by friction, the greater will be our success. 



Now, looking back over the history of the steam-engine, we may 

 rapidly note the prominent points of improvement and the most strik- 

 ing changes of form ; and we may thus obtain some idea of the general 

 direction in which we are to look for further advance. 



Beginning with the machine of De Caus, at which point we may 

 first take up an unbroken thread, it will be remembered that we there 

 found a single vessel performing the functions of all the parts of a 

 modern pumping-engine ; it was at once boiler, steam-cylinder, and con- 

 denser, as well as both a lifting and a forcing pump. 



The Marquis of "Worcester, and, still earlier, Da Porta, divided the 



VOL. XIII. 5 



