viii. Proceedings. [Jatmary yth, 19 19. 



It is clear, however, that at this time Joule did not appreciate 

 the full significance of his results, but was inclined to consider 

 them as a proof of an electric theory of Davy and Berzelius, viz. : 

 that the chemical heat of combination was a direct consequence 

 of the combination of charged atoms. It was not until some 

 time later that he modified this view and began to appreciate the 

 underlying relation between these different forms of energy. 



Then followed his research to prove the electric current 

 generated by his electromagnetic engine obeyed the same laws of 

 heating as the voltaic current, and his direct measurement of the 

 heating effect produced by the magneto-electric current by the 

 expenditure of a measured amount of work. This gave him for 

 the first time an approximate measure of J — the mechanical 

 equivalent of heat, and he was able to verify the relations 

 between heat and work when his electromagnetic engine acting 

 either as a dynamo or motor was placed in a battery circuit. 



A brief reference was made to his subsequent elaborate 

 investigations to determine the mechanical equivalent of heat by 

 the compression of gases and by friction. 



The lecturer drew attention to the remarkable experimental 

 power exhibited by Joule in these early researches, and the 

 refined methods he had introduced for the accurate measurement 

 of current, heat and work. Few men, at the age of twenty-five, 

 have exhibited such powers of accurate measurement and ability 

 to overcome experimental difificulties, or have shown such a 

 record of masterly pioneer researches. 



A brief discussion was given of the reasons why the full 

 recognition of the fundamental importance of Joule's earlier 

 researches was so long delayed and of the difficulties experienced 

 by Lord Kelvin in reconciling Joule's conclusions with the work 

 of Carnot on " Heat Engines." Adjustment of views on both 

 sides was necessary before the foundations of the new science of 

 thermodynamics were securely laid, and before the great principle 

 of the conservation of energy was generally recognised. 



Professor Haldane Gee exhibited and described some of 

 the apparatus used by Joule in his researches. These included 

 his first electromagnetic machine, parts of his later engines, an 

 electromagnet of great lifting power, a reading microscope used 

 for the calibration of delicate thermometers, and a tangent gal- 

 vanometer. Lantern slides of larger pieces of apparatus preserved 

 in Manchester were shown. Special reference was made to the 

 entries in Joule's laboratory note-books dealing with the discovery 

 of the law of electric heating and the many thousands of 

 measurements connected with the mechanical equivalent of heat. 



