l6o PRESIDENT OF BRITISH ASSOCIATION. 



valent of heat. This research originated in the discrepancy,, 

 already mentioned, between the determination by electric 

 currents (782*5), in 1867, and his final determination, in 

 1849, fr° m the friction of water (772). As this discrepancy 

 ouldc only be accounted for by admitting an error in his 

 thermal experiments, or in the unit of electrical resistance, 

 at the meeting of the British Association in 1869, a com- 

 mittee, consisting of Joule, Sir William Thomson, Professors 

 P. G. Tait, J. C. Maxwell, and Balfour Stewart, was ap- 

 pointed. By this committee Joule was charged with the 

 investigation for verifying his previous results by the direct 

 method, and attaining, if possible, greater accuracy. The 

 preparation for the research took long and was interrupted. 



In 1872, Joule was elected President of the British 

 Association for 1873, an d accepted the office. He had 

 prepared his address, when, within a few months of the 

 meeting, his health gave way, and the symptoms were so 

 serious that he was advised he would not be able to 

 discharge the duties he had undertaken. The council had 

 recourse to Professor Williamson, who kindly undertook the 

 office at the last moment, and prepared an address, the 

 preamble of which is as follows : — 



" Instead of rising to address you on this occasion, I had 

 hoped to sit quietly amongst you and to enjoy the intel- 

 lectual treat of listening to the words of a man of whom 

 England may well be proud — a man whose life has been 

 spent in reading the book of nature for the purpose of 

 enriching his fellow-men with the knowledge of its truths — 

 a man whose name is known and honoured in every corner 

 of this planet to which a knowledge of science has pene- 

 trated — and, let me add, a man whose name will live 

 in the grateful memory of mankind as long as the records 



