MEE 
where y is the electrical conductivity of a cube of unit volume, 
N the density of the free electrons, / their mean free path, 9 their 
molecular speed, and ¢ the speed of light, « the elementary charge 
and «7 the kinetic energy of a free eleetron while 7’ is the 
absoluie temperature. Putting pd “ this becomes 
ae aly 1 
PNL 
a. Vita 
CV le 
and according to Rincke if g = , Where « is the distance 
a (1 + ps)? 
between the atoms supposed to be cubically arranged, s the ordinary and 
7, the absolute temperature of the melting point, 3in Rrecke’s notation the 
: : : q bee 3 ; 
coefficient of linear expansion, £ = Vr Instead of this hypothesis of 
Rinckr’s we shall put 
L= 
V By 
in which 
Bp 
iE he == SR >. =e 
7 
e —Ì 
where 8 = 4.864.101, now represents, according to PrANckK, the 
energy of a vibrator whose frequency is r. The product Br we will 
call as usually is done a. 
We then get for the ratio of the conductivity 7, a any tempe- 
rature: 7’, to y, that at 0°C. the value: 
HP ye Ty Bore. 
on Ve 
This formula gives, in fact, good expression to the decrease with 
temperature of the resistance of pure metals of the kind here consi- 
dered (monatomic ¥). It shows in the first place the decrease to zero 
at a temperature above the absolute zero. For @p =a = 54 the 
resistance at helium temperatures becomes “about 0.0001 times 
that at O°C. 
a 
If we may further assume that pe already small at 0°C., then the 
resistance wy at 7’ in terms of the resistance w, at O° C. becomes 
0 
