12'2 PROCEEDINGS OF THE AMERICAN ACADEMY. 



and the temperature coefficient deduced therefrom will be too small to be 

 worth writing down, 0.0000 ?, let us say. 



But the recent work of Calleudar and Barnes * gives for the specific 

 heat of water 



0.9992 at 25° C. 



0.9987 " 30° C. 



0.9992 " 55° C. 



1.0000 " 60° C. 



If these values given by Callendar and Barnes are adopted as correct, 

 my first values of k will stand almost without change ; and I shall there- 

 fore leave them for the present without correction for variation in the 

 specific heat of water. 



My value for the temperature coefficient, 0.0003 or a little less, is, so 

 far as it goes, a corroboration of the substantial accuracy of the tempera- 

 ture coefficient found by Lorenz, 0.0002282, although it may be doubted 

 whether the last three figures of this number are of much significance. 

 This agreement is eminently satisfactory to myself; for a comparison of 

 the work of Lorenz with that of other investigators has convinced me 

 that his value of the temperature coefficient is entitled to an especial 

 degree of confidence. 



Measurements of the electrical resistance of the iron were made on nine 

 cylinders, each 2 cm. long and about 0.23 cm. in diameter, cut from the 

 same great bar as the disk on which the measurements of k were made. 

 The length of the cylinders, like the thickness of the disk, was taken 

 parallfel to the length of the bar ; and the cylinders were cut from a part 

 of the bar adjacent to that from which the disk was cut. The extreme 

 difference in the specific resistances of these cylinders was apparently 

 about 5 per cent. The mean specific resistance was found to be 12240 

 at 18° C. The mean specific conductivity, x, at the same temperature 

 would, therefore, be 817 X 10"^ C. G. S. " 



The ratio ^ -f- x is about 1716 at 0°C. 



The " thermo-electric height " of this iron, as compared with copper, 

 is about 



1028 X 10-« volts at 26°. 6 C. 

 980 " " " 41°.3 C. 

 936 " " •' 54°.5 C. 

 870 " " " 71M C. 



* Physical Review, April, 1900. 



