1415 
theory, supplemented by the hypothesis in Comm. N°. 119, that 
the resistance is caused by PLANck’s vibrators’), and by the -more 
special hypothesis that the electrons move freely through the atoms 
as long as they do not collide with the vibrators and are reflected 
as perfectly elastic bodies at the surface of the conductor, indicates 
causes which might work in that direction. The distance which the 
free electrons travel between two collisions at which they give off 
energy derived from the electric force, might become comparable 
to the dimensions of the conductor below 4°.19 K. (compare Comm. 
N°. 119 Feb. 1911 § 3, last note); the speed which they acquire 
in the electric current is perhaps no longer negligible compared 
with the velocity of the heat movement; for a certain current density 
at each temperature it might be just sufficient to bring the vibrators 
into motion, which otherwise below 4°.19 K. are stationary *). 
Considering all this, we may not take it as a matter of course, that 
Oum’s law will still hold below 4°.19 K. and a further investigation 
of this will be interesting, if it only proves that this is actually 
the case. 
As long as the contrary is not experimentally proved, we shall 
however adhere to this law, because we have first to try to refer 
the phenomena as much as possible to already known ones and so 
far on appropriate suppositions from the domain of known pheno- 
mena the results obtained did not seem incompatible with Oum’s law. 
Various possibilities presented themselves at once. A very small 
residual resistance evenly distributed throughout the whole thread 
might remain, which might be peculiar to the pure metal as such 
(§ 12a), or might be the consequence of an admixture (mixed crystais) 
1) Lenarp has recently given two important papers on the conduction of 
electricity by free electrons and carriers, which intend with a third paper to make 
a whole of his highly interesting researches on the interaction of electrons and 
atoms and the theory of metailic conduction. This gives to the latter a new and 
very promising base. In the first paper Ann. d. Physik 40 p. 414, 1913 he comes 
to the result making use of the great conductivity of metals at helium temperatures 
(Comm. NO. 119) that Oxum’s law is only valid within narrow limits for metals at 
very low temperatures; comp. further VIII § 16 of this Series. (Note added in the 
translation). 
2) At the great current densities that were attained in some of the experiments 
(see § 7), (they went up to 1000 Amp. per mm?) the question arises if even the 
change in the resistance of the conductor through its own magnetic field of the 
current through the conductor should be considered, as it might be the case, that 
the resistance in the magnetic field for mercury in this condition was much 
greater, just as it alters with the temperature for some other substances, and has 
been found te increase for mercury at hydrogen temperatures (KAMERLINGH ONNES 
and Benet Beckman, Leiden Comm. N'. 1324). 
92* 
