68 Prof. L. Lorenz on the Determination of 



accordance with other experiments, this number should be made 

 greater or less is difficult to decide ; but as the thermal conduc- 

 tivity in Neumann's experiments was not reduced to 0°, q must 

 be taken as a little less for this reason. 

 Hence, then, we may take 



2 = 0-90 at 0°C. 



as the result which may be deduced from the present experi- 

 ments with the greatest degree of probability. 



o 



The value of q thus determined is, in Angstrom's units, the 

 thermal conductivity of a metal whose electrical conductivity is 

 1, that of silver being taken as equal to 100. Through each 

 square millimetre of a surface with the thermal conductivity q, 

 whose thickness is 1 millim., there pass in each second 



q 10Q x ±u X 6Q - 60Q 



relative units of heat (1 grm. water 1° C), with a difference in 

 temperature of 1° C. at the two sides. As the thermal unit 

 used here is equal to 1000 A, and as we have found that 1° C. 

 expressed in absolute units is equal to 0-005075 A, the absolute 

 thermal conductivity corresponding to q, which we will call k, 

 is defined by 



q 1000 A QOQ . 



* ,= 600 X 0-005075 A = 828 ' 4 ^ 



From this we see that the factor by which the thermal conducti- 

 vity is reduced from Angstrom's units to absolute measure is 

 independent of A. 



With the value we have assumed above for q, 



*, = 296. 



If we designate the corresponding absolute electrical conduc- 

 tivity by k tJ we should have, in accordance with the above law, 



*i ' 



where T is the temperature calculated from the absolute zero. 

 For the freezing-point of water T is equal to 273 x 1° C, and, if 

 a degree Centigrade is expressed in absolute units, 



T = l-385A = 589xl0 7 , 

 from which 



— = 0-00468 A = 1 -99 x 1 7 . 



K 



If, now, we wish to calculate the absolute resistance of a Sie- 

 mens's unit (a column of mercury a metre in length and a square 

 millimetre in section at 0° C), we must know the ratio between 



