Degrees of Heat in Absolute Measure. 67 



results which are not concordant and which are far too low ; 

 hence we can only use the experiments of Angstrom, Forbes, 

 and Neumann, which agree pretty closely with each other, 

 although these observers made their experiments independently 

 of each other and in very difFerent c manners. We will for the 

 present use the units chosen by Angstrom, the centimetre, the 

 minute, the Centigrade scale, and as thermal unit 1 grm. of 

 water 1° C. 



o 



Angstrom* found for the thermal conductivity of 



Copper .... 58-94 at 0° C. 



Copper .... 51'63 „ 



Iron 11-927 „ 



Mercury .... 1'061 „ 



The last determination was made with a mercury column en- 

 closed in a glass tube, which was heated from the top. 

 Forbes found, in the above-mentioned experiments, for 



Iron 12-36 at 0° C. 



Iron 12-42 „ 



Iron 9-21 „ 



Neumannf determined the thermal conductivity of five differ- 

 ent metal bars, and at the same time made a comparative deter- 

 mination of their relative electrical conductivity. While this 

 was taken at 100 for silver, that of copper was assumed to be 

 equal to 73'3. These results were, with the above units : — 





Thermal 



Electrical 







conductivity. 



conductivity. 



?■ 



Copper . 



66-48 



73-3 



0-907 



Brass 



18-12 



17-9 



1-012 



Zinc . . 



18-43 



21-1 



0-873 



German silver 



6-566 



6-45 



1-018 



Iron . . 



9-824 



10-20 



0-963 



The ratio between the thermal and the electrical conductivity 

 (which is designated by q) is greatest for brass and German silver. 

 This is not accidental, but probably a consequence of the fact 

 that they are not pure metals. In like manner we obtain, in 

 agreement with what has been said above, a discordant and ob- 

 viously too low value for mercury ; we find for this metal, from 



Angstrom's experiments, £ = 0-617, taking as the electrical con- 

 ductivity of mercury 1*72. 



The mean value of the quotients q for copper, zinc, and iron 

 is 0'914 according to Neumann's experiments. Whether, in 



* Pogg. Ann. vol. cxviii. p. 423, and vol. cxxiii. p. 628. 

 Ann. de Chim. et de Phys. 1862, vol. lxvi. p. 183. 

 F2 



