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PROCEEDINGS OF THE AMERICAN ACADEMY. 



of temperature of one main bar over that of the other, differs so little 

 from q^ that it is not given in the table. Under q is given the final 

 value of the Thomson effect heat, obtained from ^" by taking account 

 of the amount of heat which, between the / and the h cross-sections, 

 escapes by lateral flow from the warmer bar in excess of that which 

 escapes in the same way from the cooler bar. This correction, which 

 is large, usually about 23 per cent of the value of q, will be discussed 



A 



at some length later. Under o- is given q^ —{th — t^ ; that is, the 



mean Thomson effect heat per electromagnetic unit of current per 

 degree of the range of temperature considered. Under v is given 

 cr -7- (273 -{■ \{ti\ h)), which may be called the mean Thomson effect 

 coefficient between ti and t;, : 



The difference, about 5 per cent, between i'e, the value of v obtained 

 with the east end the hotter, and v^, the value obtained with the west 

 end the hotter, as shown in the table just given, has been the subject 

 of a great deal of cogitation, and a thoroughly satisfactory explanation 

 of it has not been found. It is unlikely that the whole difference was 

 purely accidental in the sense that it would have disappeared in a pi-o- 

 longed continuation of the experiments ; for the smallest I'p. is larger 

 than the largest v^. It is true that fi and 4 were determined only 

 once with the east end the hotter, which will now be called the state E ; 

 and, moreover, the conditions during this determination were not of the 

 best, so that it may well be doubted whether the true value of h — ti 

 was any greater with state E ^^ than with state W. If we assume that 

 the two values were the same, the difference between the mean v^ and 



1^ A redetermination of tliis quantity for condition E after tlic observations 

 of April 17-18 was prevented by a partial breaking down of the apparatus, which 

 mishap will be described later. 



