912 
circumstances mentioned above under a and ¢ also play a part}). 
The latter of these, viz. a change of the elastic properties with the 
temperature, would be connected with deviations from the linear 
relation between the forces between the molecules and their relative 
displacements, which deviations DeBiJr*®) also makes responsible for 
the thermal expansion. 
In table V are given the values of 7, which are obtained by 
applying Depisn’s formula for C, to the individual observations. They 
are united in Fig. 11 *) ‘). 
1h 24 36 48 60 72 84 
Fig. 11 
$ 6. Copper. With copper we were as yet only able to make a 
series of measurements between 15 and 22° K. The copper was 
electrolytic copper of FerLTEN and GurLLauMe, 596,0 grammes. 
U, in table VII represents the mean atomic heat between the 
initial and final temperatures; for correction to the “true” atomic 
1) Regarding a it may still be remarked that the presence of a second modifi- 
cation of appreciably different properties in a considerable quantity would lead us to 
expect much larger deviations from DepBie's formula than appear actually to 
exist. If the circumstance mentioned under a plays a part, we therefore have to 
assume a small quantity of a second modification, or a second modification 
whose elastic properties are only little different from those of the first. 
2) P. Depise, Vorträge Wolfskehlcongres Göttingen 1913. 
3) The slow change, which EuckEN and ScHwers le. observed in the values 
of § for lead as derived from their measurements, and which does not coincide 
with that found by us, is considered by them as probably due to the uncertainty 
of the temperature coefficient of their resistance thermometer. 
4) Fig. 11 gives a special illustration of the character of the deviations from 
Desise’s formula over the whole range, and can also serve to calculate a smoothed 
value of C, by reading the value of 6 corresponding to a definite 7 from the 
smoothed curve. At the same time it should be remarked, that the values of 4 
represented in Fig. 11 do not coincide with hymaz/k, if ymax, the maximum frequency 
according to Desi, changes with 7. 
