300 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



nal or internal means, would have, of itself, no tendency to establish 

 any mean difference of potential between the ujjper and under faces 

 of the disk. 



It appears, therefore, to be established that A does represent — that 

 is, is proportional to — the mean difference of temperature between the 

 upper and under faces of the disk.* 



It may be of interest to compare the difference of potential curves 

 of the various series of experiments. If in Figure 10 we take the 

 mean of A and B, we get a new curve, which may be taken as repre- 

 sentative of the potential conditions, or difference-of-potential coudi- 



Aug. 22 



tions, prevailing in the experiments at low temperature on September 

 2. Combining each A curve for low temperatures with its correspond- 

 ing -B curve, and plotting the resultants, we get Figure 12, except the 

 heavy line, which is obtained by taking the mean of all the others 



* Cf . an article, by Prof. B. O. Peirce, " On the Properties of Batteries 

 formed of Cells joined up in Multiple Arc." These Proceedings, Vol. XXX- 

 p. 194. 



