582 bepokt — 1884. 



increase. This is, however, a matter for the treatment of which space 

 cannot here be taken. Rankine has devised a convenient method of 

 solving such problems, involving this condition, as may arise in practice, 

 where cylinder-condensation may be neglected, and the writer has found 

 a method of adapting it to ordinary practice. The subject will ultimately 

 form, properly, a final division of the complete theory of the steam- 

 engine. 



Chronologically considered, it is seen that the history of the growth 

 of the theory of the steam-engine divides itself distinctly into three 

 periods, the first extending up to the middle of the present century, and 

 mainly distinguished by the attempts of Carnot and of Clapeyron to 

 formulate a physical theory of the thermodynamics of the machine; the 

 second beginning with the date of the work of Rankine and Clausius, 

 who constructed a correct thermodynamic theory; and the third beginning 

 a generation later, and marked by the introduction, into the general 

 theory, of the physics of the conduction and transfer of that heat which 

 play no part in the useful transformation of energy. The first period 

 may be said to include, also, the inauguration of experimental investiga- 

 tion, and the discovery of the nature and extent of avoidable wastes, and 

 attempts at their amelioration by James Watt and by John Smeaton. 

 The second period is marked by the attempt, on the part of a number of 

 engineers, to determine the method and magnitude of these wastes by 

 more thorough and systematic investigation, and the exact enunciation of 

 the law governing the necessary rejection of heat, as revealed by the 

 science of thermodynamics. The third period is opening with promise 

 of a complete, and practically applicable, investigation of all the methods 

 of loss of energy in the engine, and of the determination, by both 

 theoretical and experimental research, of all the data needed for the 

 construction of a working theory. 



M. Him has recognised these three periods, and has proposed to 

 call the second the ' theoretical,' and the third the ' experimental ' stage. 

 The writer would prefer to make the nomenclature somewhat more 

 accordant with what has seemed to him to be the true method of develop- 

 ment of the subject. It has been seen that the experimental stage really 

 began with the investigations of Watt, in the first period, and that the 

 work of experimentation was continued through the second into the 

 present — the last — period. It is also evident that the theoretical stage, if 

 it can be properly said that such a period may be marked off in the 

 history of the theory of the steam-engine, actually extends into the 

 present epoch, since the work of the engineer and the physicist of to-day 

 consists in the application of the science of heat-transfer and heat-trans- 

 formation, together, to the engine ; during the second period the theory 

 included only the thermodynamics of the engine ; while the third period 

 is about to incorporate the theory of conduction and radiation into the 

 general theory, with the already established theory of heat-transformation. 

 The writer would therefore make the classification of these successive 

 stages in the progress here described, thus : — 



(1.) Primary period. — That of incomplete investigation, and of 

 earliest systematic, but inaccurate, theory. 



(2.) Secondary period. — That of the establishment of a correct ther- 

 modynamic theory, the theory of the ideal engine. 



(3.) Tertiary period. — That of the production of the complete theory 

 of the engine, of the true theory of the real engine. 



