( 684 ) 
ascribed accordingly to the lengths at 0° C. of the points projecting 
beyond A and PD follow from the equations. These equations give 
La, + Ls, = 16.587 and Ly, + Ls, = 23.095 for Jena and Thüringer 
glass respectively, and further; 
GD, (Lt at = bt) 
V=Vi(1+4,t+h,0) 
Jena glass 16™ (a — 7.74, 10 ®,b = 0.00882. 10 ° 
k= 28:21. 105 k;=0:02655 2055 
(TAOS mdr (0) rey 
| 9.15 10-§,b = 0.0119 10-6 
Thüringer glass (n°. 50) ; 
( k, =27.45 10-6, k, = 0.0357 10-6 
The value found for Jenaglass 16"! differs much from that obtained 
by Wiese and Börrcuer®) and from those obtained afterwards by 
TrieseN and Scueer ®) for temperatures between 0° and 100°. 
Physics. — “The motion of electrons in metallic bodies, UI.” By 
Prof. H. A. Lorentz. 
(Communicated in the meeling of March 25, 1905). 
§ 16. We may now proceed to examine the consequences to 
which we are led if we assume fwo kinds of free electrons, positive 
and negative ones. We shall distinguish the quantities relating to 
these by the indices 1 and 2; e.g. N, and NV, will be the numbers 
of electrons per unit of volume, m, and m, their masses, oh and oh 
ofl, te 
the mean squares of their velocities. For simplicity’s sake, all elec- 
trons of the same sign will be supposed to be equal, even if con- 
tained in different metals. As to the charges, these will be taken to 
have the same absolute value for a// particles, so that 
i mre ora (45) 
Our new assumption makes only a slight difference in the formula 
for the electric conductivity ; we have only to apply to both kinds 
of electrons the considerations by which we have formerly found the 
equation (21). Let a homogeneous metallic bar, having the same 
temperature throughout, be acted on in the direction of its length 
by an electric force EE; then, just as in $ 8, we have for each kind 
of electrons 
1) In the original was given 
Jena 161! «@=7.78 b=0.0090 
Thüringer n° 50 a=9.10 b=0.0120. 
2) Wiee und Börrener. Z. f. Inst. k. 10, pg. 234. 1890. 
3) Turesen und Scneer, Wiss. Abt. der Ph. techn. Reichsanstalt. Bd. ILS. 129. 1895, 
