40 PROCEEDINGS OP THE AMERICAN ACADEMY. 



worked out values of cr for several temperatures, with various assump- 

 tions as to the thermal conductivity of his copper and the radiation from 

 its surface. The smallest value of v which comes from any of his esti- 

 mates of a- is 103 x 10" 10 at 208°; the largest value, 174 X lO" 10 at 

 122°. 



The fact that King's smallest value of v is considerably larger than the 

 value of v c deduced from the v t - found in this paper for iron may indicate 

 that the v t as here found is somewhat too large. It is to be observed that 

 a reduction of a little more than two per cent in the numerical value used 

 for v, would bring the value of v c up to the minimum value found from 

 King's data. It is quite possible that the value 757 X 10 -10 found for 

 v t is several per cent in error. 



We are at present making preparations for a study of the properties of 

 our iron between 100° C. and 200 ° C. 



It may be advisable to make a direct determination of the Thomson 

 effect in copper and various other metals with apparatus like that de- 

 scribed in this paper, but the difficulty of a direct study of copper would 

 be very considerable. 



The properties of the very soft iron studied in this paper, so far as they 

 are quantitatively known, are summarized below : 



Composition : iron, 99.93 % ; carbon, 0.059%. 



Density : about 7.785 at 0° C. 



Thermal conductivity, k: 0.1528 at 28.2° C, 



with a temperature coefficient 0.0003 (?) from 28° to 58° , 

 « " " " 0.0007 (?) " 13° « 87°, 



the latter value being the more reliable. 

 Electric resistance, absolute : 11365 at 0° C, 



with a mean temperature coefficient 0.00519 from 0° to 100° . 



'' Thermo-electric height " with copper : 



f 1028 X 10- 8 volt at 26.6° C, 

 980 " « " 41.3° , 

 936 " " " 54.5° , 

 870 " « « 71.1° , 



approximately 



Thomson effect coefficient, v : 



i - 757 X 10- 10 mean, from 13° to 90° , 



approximately -'715 u " « « " 51° , 



I — 793 « " " 51° " 90°. 



