Electric Origin of Rigidity and Consequences. 433 
For the thermal conductivity & we have with s=2a, 
k=26Q(2a)77AaO2(Co*r, . . . . (21) 
ramey bk) k/y=A4fAaG/3e. Soa gare site) es NEED 
This is the central relation of the theory of Riecke and Drude. 
It embodies the Wiedemann-Franz law. Drude’s theory 
makes 7 identical with 2 and A=1. Then, with the values of 
y and & for silver at 18° C. and J. J. Thomson’s value 
of eas 6x 10-!°, he finds for a the value 26°5 x 10—", while 
in the kinetic theory of gases it is 5°6 x 10—-". As Thomson 
has found 3x 10-! to be a better estimation of e, Drude’s 
value of e becomes 13x10-". This is near enough to the 
kinetic theory value to show that Drude’s assumption that 
the kinetic energy of an electron equals that of a molecule is 
substantially correct. Thus the free electron of the Riecke 
theory at a given temperature has the same kinetic energy as 
a molecule of gas at that temperature. The present theory 
does not necessitate the literal truth of Drude’s principle. 
All that we need to assume is that an electron in moving 
from one place to another carries to its molecule in the second 
place an amount of energy nearly equal to its excess or 
defect over the molecular energy at the first place. The 
simplest way of giving the electron this property is to treat it 
asa molecule of a perfect gas, but it is nottheonly way. By 
means of the data of Jaeger and Diesselhorst (Sztz. d. k. pr. 
Akad. der Wiss. Berlin, 1899) for y and & for a number of 
pure metals on the same specimens at 18° and 100°, Drude 
shows that while according to (22) the ratio of k/y at 18° 
and at 100° is 373/291=1°28, the experimental values range 
from 1:26 for Sn to 1°35 for Pt and Pd, the mean for 13 
metals being 1°30. For the exceptional metal Bi it is 1:12. 
But according to (22) k/y ata given temperature ought to be 
the same for all metals. Here are the values given by Jaeger 
and Diesselhorst :— 
moe ee” An, Ni- gn, Cd. Pb. Sn..- Pt. Pd Fe. Br 
636 665 686 727 699 672 706 715 735 753 754 802 962 
If we except Fe for its strongly magnetic properties and 
Bi on account of its crystalline structure, we find k/y increase 
from 636 for Al to 754 for Pd. It is of interest that for 
these same metals the atomic heat Mc increases in about the 
same proportion, as the following values of 10Mc show when 
arranged for the metals in the same order as above. The 
values of ¢ used are Regnault’s at about 60°C. A row of 
Phil. Mag. 8. 6. Vol. 7. No. 41. May 1904. 2H 
