550 PROCEEDINGS OP THE AMERICAN ACADEMY. 



the sensitiveness of the galvanometer. The numbers given under 

 A 2 or B 2 , etc., are the galvanometer deflections observed on reversal 

 of a commutator in the thermo-electric circuit containing the couple 

 referred to : 



Time. Sensitiveness. 



1:15p.m 21.20 



3:05 " 21.20 



5:25 " 21.19 



Mean 21.20 



A 2 B 2 C 2 D 2 Temperatures. 



1:40 p.m. ( 19.84 19.66 20.03 



"Parallel"-^ 19.80 



2:55 " / 19.86 19.67 20.04 180°.36 140°.12 



19.85 19.67 20.04 19.80 



4:05 " (19.68 19.85 19.36 



"Crossed"-^ 19.74 



5:20 " / 19.71 19.85 19.38 180°.36 140°.07 



19.70 19.85 19.37 19.74 



Means. . 19.77 19.76 19.71 19.77 180°.36 140°.10 



Mean of all = 19.75 Diff. = 40°.26 



These data yield the following values : 

 Mean total e. m. f. = 958 X 10 -6 volt, 



" e. m. f. per degree, between 140°.10 and 180°.36 = 2378 X 10~ 8 volt. 



Putting aside, for the present, consideration of the absolute values 

 here indicated, we may observe a number of comparative features which 

 are of interest: 



First, that the smallness of the difference between the earlier and 

 the later deflections obtained with the same couple in each of the two 

 groups " parallel " and " crossed " is good evidence that practical ther- 

 mal equilibrium was attained before the beginning of each of these two 

 groups of observations. Even the slight tendency here observed toward 

 increase of the deflections with progress of time is greater than was 

 usually evident. 



Second, that in each of the two groups, " parallel " and " crossed," 

 considerable differences between the deflections yielded by different 



