487 



those of 1914, vi:. 0.023 joules/degree at 15° K., and 0.038 joules/ 

 degree at 20° K.') 



Tliis difference can be explained bj the fact that for the meas- 

 urements of 1915 on Kjji for the wires wliich carry the heating 

 current a little less platinum had been used. This circumstance was 

 taken into account as far as possible. 



§ 3. Atomic heat, of copper.'^) For the measurements the same 

 block of copper was used as for those of Comm. N°. 143 § 6 : 

 electrolytic copper of Felten and Guillaume, 596,0 grammes. 



As a check on the |)urity of the copper after the measurements 

 a strip was cut from the block; the strip was tiled to a rectangular 

 section, then rolleil and annealed. The resistance was then measured 

 at room temperature and in liquid hydrogen'). 



1) The measurements of 1914 being corrected for the change of AiiiS. 



2) The atomic heat of copper has already been measured between 23 and 

 88° K. by W. Nernst, Ann. d Phys. (4) 36 (1911), p. 395. 



3) We took advantage of this opportunity to test at the same time the purity 

 of the lead which we had use.l for the measurements on this metal of Gumm. 

 W. 143. and to invest gate tlie influence of the treatment of the metal on tlie 

 decrease of the resistance. The results are collected in the following table. 



These data lead to the following conclusions regarding the influence of the 

 treatment of the metal on the change of the resistance with change of temperature: 



For copper rolling diminishes the decrease of the resistance between room tem- 

 perature and the boiling point of hydrogen in a large degree. 



By subsequent annealing the influence of rolling Ihe copper is not only annulled, 

 but the decrease of the resistance between the temperatures mentioned above is 

 now even greater than that of copper which has not been rolled and annealed; 

 apparently annealing lias also annulled the influence of previous mechanical treatment 

 (filing), probably in consequence of Ihe lact that the metal has united again to 

 larger crystals. 



The temperature-coefficient at hydrogen temperatures undergoes only a small 

 change by the manipulations mentioned above. 



The change of the resistance of lead suffers no or only a small change by rolling. 



