572 



iiKPouT — 1884. 



inevitably and unavoidably, so far as is to-day known, concur in the pro. 

 duction of a waste of energy. 



Of all the lieat sent forward by the steam boiler to the engine, a certain 

 part, definite in amonnt and easily calculated when the power developed 

 is known, i'. expended by transformation into mechanical energy; another 

 part, equally defir ito and easily calculate 1, also, is expended as the nooes- 

 sarily-occurring waste which must take place in all such transformations, 

 at nsual temperatures of reception and rejection of heat ; still another 

 portion is lost by conduction and radiation to surrounding bodies; and, 

 finally, it part, often very large in comparison with even the first and 

 principal o*' these quantities, is wasted by transfer within the engine, from 

 the induction to the eduction side, from ' steam to exhaust,' by a singular 

 and interesting prc^ ess, without conversion into useful effect. The science 

 if thermodynamics only takes cognisance of the first, which is sometimes 

 one of the smallest of these expenditui-es. 'I'ho science of the genenil 

 physics of heat takes cognisance of the others. 



The science of the phenomena of the steam-engine must, like every 

 other branch of applied science, be considered as the product of two dis. 

 tinct processes of development : the one is what maybe called the expen- 

 mental development of the subject, the other is the purely theoretical 

 progi'css of the science. So far as the useful application of principles to 

 the perfection of the machine is concerned, the latter has always, as is 

 usually the case elsewhere, been in advance of the former in its deduction 

 of general principles; while, as invariably, the former has kept far in 

 advance, in the working out of practically useful results, and in the deter- 

 mination of the exact facts where questions of economic importance have 

 arisen. It is proposed hero to follow the history of the experimental 

 development of the principles controlling the etficiency of the engine, and 

 modifying the conclusions derived by the application of the science of 

 heat transformation, after first tracing the progress of the development of 

 that science. The gradual formation of the pure theory of the steam- 

 engine will be traced, and the limitations of that theory will naturally 

 come up for consideration afterward. 



The germ of a science of the steam-engine may be found in the woik 

 of Sadi Carnot, published just sixty years ago. Although familiar with 

 the then doubted mechanical theory of heat, he was not sulliciently well 

 convinced of its correctness, .apparently, to make it the basis of his work. 

 but assumed, throughout his ' il^;//e,l'/rt?^s• sur la I'uhnaiire Midrice du Ftn,' 

 the theory of substantial caloric. Nevertheless, in his development of 

 the theory of heat-engines, he enunciated some essential principles, and 

 thus laid the foundation for a theor^^ of the steam-engine which was given 

 correct form, in all its details, as soon as the dymimical theory was taken 

 for its foundation principle. 



Carnot asserts that ' the motive power of heat is independeut of the 

 means taken to develop it ; its amount is determined simply by tlip 

 temperature of the bodies between which the heat is transferred. 

 Wherever there exists a difference of temperature, there may be a develop- 

 ment of power. The maximum amount of power obtainable by the use 

 of steam is the maximum obtainable by any means whatever. High- 

 pressure engines derive their advantage over low-pressure engines simply 

 from their power of making useful a greater range of temperature.' He 

 made use of the device known as the ' Carnot Cycle,' exhibiting the 

 successive expansions and compressions of the working fi.uid in heat- 



