1 8 Dugald Clerk, The Work and Discoveries of Joule 



into effective existence by the work of the engineer and 

 experimenter. Scientific research in physics and chemistry 

 is of two' kinds; one kind deals with the nature of the pheno- 

 mena observed, and endeavours to arrive at some soul- 

 satisfying- explanation of the why and wherefore of the 

 particular occurrence; the other endeavours to discover 

 hitherto unknown phenomena. Naturally the earlier scientific 

 investigations dealt with known phenomena, and one type of 

 discovery consisted in determining their laws. So far science 

 has often been able to supply the law, but never the explana- 

 tion. Many laws are known with accuracy, but all reasoning 

 on the facts leads up to the contradiction which inevitably 

 follows the closer application of thought to theories of gravi- 

 tation, cohesion, light, electricity, chemical action and life ; 

 all appear equally inexplicable. 



It is an error, then, to assume, as many scientific men do, 

 that the evolution of a great invention usually follows the 

 course in which the abstract investigator discovers the pheno- 

 mena and determines the laws and the inventor and designer 

 applies these laws and facts to the practical work. Generally 

 the invention has come into* being at a time when the laws of 

 its operation were but vaguely known and the stimulus of the 

 successful practical machine led to its abstract investigation 

 to explain its action. This is most important work, because 

 such investigation supplies data to enable the inventor to 

 reason accurately on the next' step of improvement. In my 

 own experience of the past forty years I have been able to 

 apply Joule's discovery to the investigation of the theory of 

 internal-combustion engine cycles of operation, and I have 

 been able in conjunction with others to deduce the laws of 

 imperfect cycles and so to calculate with accuracy the limits 

 of thermal efficiency possible in those important heat motors. 

 After many years of work the internal-combustion engineer 

 is able to determine with confidence the line of advance in the 

 modifications of such engines. In my own time brake thermal 

 efficiencies in gas and oil engines has risen by constant reason- 

 ing and experiment from 16 per cent, to 35 per cent, of the 

 total heat supplied to the engine. At the same time the 

 practical experiments made have suggested new lines of 

 investigation to scientific men, from which investigations 

 many new laws have been discovered of equal abstract and 

 technical interest. 



The debt of the practical engineer to Joule and his great 

 associates is very real, but it is not the type of debt to which 

 I have already referred. That is, the science of thermodyna- 



