Manchester Memoirs, Vol. Ixv. (1921), No. 3 19 



mics did not supply the fundamental laws from which heat 

 engines were invented and developed. What was true of the 

 Steam engine was also true of the hot air engine and the 

 internal-combustion engine ; all the known types of heat 

 engine at present in use were invented before the year 1850 

 and practical experimental examples of both hot air and 

 internal-combustion engines were then in operative existence. 

 Thermodynamics supplied the laws of the conversion of heat 

 into mechanical work by which these engines were governed ; 

 it explained the relative perfection of engines already in 

 existence ; it did not create these engines. It performed the 

 very important service of dispelling the errors of thought 

 which hindered the future advance of heat engines. Such 

 errors as I have described as to the theory of the regenerator, 

 theory of compression and expansion in all steam and internal 

 combustion engines, held by the most eminent engineers and 

 scientific men so late as from 1845 to 1853, were rendered 

 impossible by the splendid work of Joule, Kelvin, Rankine and 

 their continental colleagues. The knowledge of thermo- 

 dynamics has thus an increasing effect upon instructed 

 engineers of the present generation. It is quite obvious that, 

 although the origin of heat engines cannot be ascribed to 

 Joule's work, yet the improvement and final development 

 towards a maximum conversion of heat into mechanical work 

 is rendered possible to the engineer of to-day by his great 

 discoveries. Engineers and engine designers are most grate- 

 ful to 1 Joule and look back on his achievements as those of the 

 utmost intellectual and practical importance. 



Joule's service to science and mankind are of even greater 

 value : all intellectual discoveries are of the utmost importance 

 to the race. The highest interest of man is found in the 

 development of the intellect ; it is there that consciousness of 

 man differentiates him from the other creatures of the earth. 

 Our knowledge of objective things is, after all, purelv sub- 

 jective, and our belief in the existence of objects external to 

 ourselves gives a vivid interest to the pursuit of knowledge 

 of the real things which we feel exist behind the veil of 

 subjective sensations and impressions. The knowledge called 

 scientific is, after all, but knowledge of the sequences of 

 occurrences as observed through our senses and imagined by 

 our consciousness. Great discoveries such as those of Joule 

 greatly increase our grasp of the sequences of physical nature 

 and enable us to predict to some extent the future development 

 of the world in which we live. Joule, like all great discoverers, 

 aids the race to rise by the development of the intellect. 



