344 Literary and Philosophical Society. 



' If we make the time and the resistance of the wire 

 constant, the above equation becomes simplified to 



y=nr ' 



* If the current and time are constant, we have 



y = ~j-^ .... 3 



' I have made several series of experiments, using the 

 same conducting wire as a source of heat, a constant inter- 

 val of time, and a variable current of electricity. The 

 method adopted in these experiments was, to try the effect 

 of a wire traversed by a current of electricity, — first, when 

 it was immersed in water, and afterwards when it was im- 

 mersed in another liquid. Hence I obtained two deter- 

 minations of y in equation 2, one of them for water, the 

 other for the liquid. The relation between these two 

 quantities gave, of course, the capacity of the liquid com- 

 pared with that of the water.' 



Without pretending to say that it was impossible to 

 arrive at Joule's conclusions without the atomic theory of 

 Dalton, we may say distinctly that it was not attained 

 without its aid. The idea of full portions, units of measure in 

 Dalton's mind, developed itself gradually into itniis of force 

 in the mind of Joule, and it is in this form that we received it 

 from the hand of one illustrious member still active amongst 

 us. To say that the two are the most successful descendants 

 of the great thinkers who have grappled with the subject of 

 atoms for three thousand years is but to express a simple 

 fact ; and to assert that Dalton and he have made the 

 great leading discoveries on the subject is simply to follow 

 history. From one we learn the order in which the ultimate 



