52 



PROGRESS OF SCIENCE 



was brought about ' by the wish to find a common 

 link binding together all the forces which in each 

 branch of physics gravity, electricity, magnetism, 

 and chemistry had been treated as peculiar to that 

 branch. ' As for Joule's researches into the mechanical 

 equivalent of heat, it is for our purpose sufficient to 

 recall his relations with the Association in connexion 

 with them. He communicated his first ideas as to 

 the mechanical equivalent of the quantity of heat 

 capable of increasing the temperature of a pound of 

 water by 1 F., to the Chemical Section at the Cork 

 meeting in 1843 ; when they were received with the 

 silence of disapproval. In 1845, at Cambridge, a 

 further paper from him aroused no discussion. A 

 third paper at Oxford, in 1847, might have suffered 

 a like fate, but it was heard by both Faraday and 

 Thomson (Kelvin), the second of whom perceived, 

 as he afterwards wrote, that 'it contained a great 

 truth and a great discovery/ He entered promptly 

 upon a discussion of the matter whether openly in 

 the section is not clear, but certainly with Joule 

 personally and from that occasion there date at 

 once the gradually extending acceptance of Joule's 

 results and an intimate relationship between his 

 labours and one department of Kelvin's many ac- 

 tivities. Kelvin's demonstration of the ' universal 

 tendency to the dissipation of mechanical energy ' 

 supplemented Joule's results. Clerk Maxwell 

 (1831-79) supplemented Faraday's experiments in 

 electricity by mathematical demonstration. 



Joule was prevented by ill-health from being 

 president of the Association at the Bradford meeting 

 in 1873. Sir Oliver Lodge, recalling this as the 

 first meeting attended by him, writes thus of it : 



