September 26, 1884.] 



SCIENCE 



307 



having been taken, it becomes a duty, not to 

 ignore that, but to seek the knowledge needed 

 before the next step can be taken. In this de- 

 partment also, as in others, the theorist has 

 often failed to realize, that, although his math- 

 ematically de- 

 duced conclu- 

 sions indisput- 

 ably follow 

 from his as- 

 sumed prem- 

 ises, the latter 

 may be, never- 

 theless, so far 

 different from 

 the conditions 

 of actual work 

 as to render 

 his deductions 

 practically val- 

 ueless and ab- 

 surd. 



The last- 

 mentioned of 

 the two classes 

 of phenomena 

 are now be- 

 coming well 

 recognized as 

 essential ele- 

 ments in the 

 action of all 

 heat-engines, 

 and it will not 

 be long before 

 investigators 

 now at work 

 will bring into 

 view all the 

 facts needed 

 in the task of 

 tracing out the 

 laws control- 

 ling this meth- 

 od of expendi- 

 ture of heat ; 

 and its intro- 

 duction into 

 the theory of 

 the steam- 

 engine will promptly follow. The writer has 

 already endeavored to frame a closely ap- 

 proximate theory of the steam-engine on this 

 basis, using the facts already known, and 

 taking expressions for this method of waste 

 which experiments already made indicate to 

 be tolerably exact ; sufficiently so to permit 

 their use in design until further research shall 



give us more precise, though perhaps less con- 

 venient, expressions. The results so attained 

 accord very satisfactorily with experience. 

 This last period in the history of the theory 

 of heat-engines has been inaugurated by the 



very valuable 

 labors in Great 

 Britain of Pro- 

 fessor Cotter- 

 ill, who seems 

 to have been 

 the first author 

 to take up the 

 new phase of 

 the subject 

 with the in- 

 tention of mak- 

 ing practically 

 useful applica- 

 tion of existing 

 knowledge ; 

 and, on the 

 continent o f 

 Europe, by 

 the interest- 

 ing, if some- 

 what warm, 

 discussion of 

 the defects of 

 the theory of 

 the second 

 period, be- 

 tween Messrs. 

 Hirn and Hal- 

 lauer, on the 

 one hand, and 

 Professor Zeu- 

 ner, on the 

 other; and 

 also, in this 

 country, by 

 the attempt to 

 rationalize the 

 accepted the- 

 ory to which 

 allusion is 

 made above. 



The experi- 

 ments upon 

 which we are 

 to-day dependent in this work of revolutioniz- 

 ing the theory of heat-engines, and which have 

 revealed the limitations to which the economical 

 application of heat as a motor in the steam and 

 other heat engines is subject, began with James 

 Watt, who a hundred and twenty years ago, by 

 his investigation of the action of steam in the 

 cylinder of the Newcomen engine, revealed 



