Manchester Memoirs, Vol. Ixv. (1921), No. 3 17 



dynamic laws, because it requires accurate knowledge of the 

 properties of the working fluid dealt with under conditions 

 rendering- observation extremely difficult. The modern inter- 

 nal-combustion motor is the successor to the air engine so 

 fully discussed by eminent engineers of sixty-seven years 

 ago; and the forebodings of even so eminent a man as Faraday 

 as to its ultimate success have proved unfounded. Great 

 difficulties have been encountered and many discrepancies 

 have had to be explained, but a minute study of the nature of 

 the working fluid has rendered it more and more possible to 

 calculate the efficiencies to be expected under practical condi- 

 tions. At the present time we can deal with almost any cycle 

 or any working fluid with some fair approximation to an 

 accurate result. Much work, however, is required before all 

 problems of the working fluid can be said to be solved with 

 regard to any heat engine. Indeed, it may be said that under 

 modern conditions of the use of steam even the properties of 

 the working fluid — steam — have not yet been completely 

 determined. 



Notwithstanding all the perplexities involved in the minute 

 study of the imperfect heat engine cycles, we are in a very 

 different position to-day compared with the engineer of 1853. 

 We know all 'the broad laws as to the conversion of heat into 

 work or of work into heat ; and, numerous as are the problems 

 yet to be solved, we at least profit by the guiding light set out 

 for us by Joule with Kelvin and Rankine. 



The science of thermodynamics is thus on one of its sides 

 an explanation of the laws of operation of heat engines already 

 in existence. In the case of the electric light, the dynamo and 

 motor ; practice and invention began with the scientific 

 discovery of Faraday of the induction of electric currents by 

 magnets in the year 183-1. But it took over thirtv years by 

 hundreds of investigators and inventors to develop from 

 Faraday's fundamental facts the mass of knowledge necessary 

 to design and construct great central stations with distributing 

 systems and incandescent lamps and motors required to 

 supply a city with light and power. Faraday's discovery was 

 a necessary step in the progress, but many later steps were 

 required together with a huge expenditure of capital before 

 practical success was ultimately attained. Differing tvpes of 

 workers, such as technical men, inventors and capitalists were 

 all equally required. 



In the case of the steam engine science sprang from the 

 reasoning on the facts of practice, and the science of thermo- 

 vdynamics explains the action of great mechanisms brought 



