G-A Prof. Neumann on the Calorific Conductibility of Solids. 



The first observations which I made in this way, three years 

 ago, only refer to the course of the experiments ; but then it 

 was necessary to use at least two bars of different lengths, or 

 rather two rings of different diameters, to determine at one time 

 the coefficients of external and of internal conductibility. I found 

 in this way the following numbers for the internal conductibility 

 of some metals, of which I determined at the same time the 

 specific gravity, and the relative electric conductibility. 





Internal calorific 

 conductibility. 



Specific 

 gravity. 



Electric 

 conductibility. 





1306 

 356 

 362 

 129 

 193 



8-73 

 8-48 

 7-19 

 8-54 



7-74 



73-3 

 17-9 

 211 

 6-4 

 10-2 





Tin 





Iron 





I took for the electric conductibility M. Wiedemann's number 

 73-3; his law of the proportionality of the two coefficients of 

 conductibility is tolerably well verified by my results, as may be 

 judged by the ratios of my numbers, which are respectively 

 17-6, ]9-8, 17'1, 19-9, 18-9; mean 18'7 : the small differences 

 from this mean are the less astonishing, as my observations do 

 not refer to the same temperature. It must also be remembered 

 that M. Becquerel found 136 for the calorific conductibility of 

 copper, M. Lenz 73, M. Riess 66, M. Bust 94, that of silver 

 being 100. 



My units are the minute, the Paris line, and the quantity 

 of heat capable of raising the temperature of a cubic line of 

 water by 1°*. When I shall have subjected all my results to a 

 uniform discussion, it is possible that the numbers may undergo 

 some slight modification. 



To investigate badly-conducting substances I had recourse to 

 another method. I made cubes 5 or 6 inches on the side, or 

 spheres of the same diameter. These bodies, having been uni- 

 formly heated, were allowed to cool in the air; and when this 

 cooling had lasted a certain time (which was from half an hour 

 to an hour), the temperatures at the centre and at the surface 

 were observed, by means of the thermo-electric rods already 

 mentioned. Their influence on the course of the temperatures 

 may always be estimated by calculation. In this way I obtained 



k 

 the following values for the ratio -^pr, k being the calorific con- 

 ductibility, c the specific heat, and D the density. 



* To reduce the above values to Peclet's units or to those of M. Ang- 

 strom, it is necessary to multiply them respectively by 0-0848 or by 00509. 



