( 685 ) 
AnlAe „ 
Shen 
The electric current per unit of area of the normal section, is the 
sum of the currents due to the positive and the negative particles. 
We may therefore represent it by 
Al, A,e,? bs 4al, Ae E 
hm, dh,m, 
and we may write for the coefficient of conductivity 
== 
OEROL ON Gyo eo (4:00) 
if 
An l Ae? dt UR Aven: 
— 1 Lara te = 2 #73 
: dh, m, ; core dh, m, 
or (cf. § 8) 
We Ue INE CE POR ie INEGI 
i= ne Men TT. (50 
: 3a al i 3a aT B 
These latter quantities may be called the partial conductivities due 
to the two kinds of electrons. 
$ 17. In all the other problems that have been treated in the prece- 
ding parts of this paper, we now encounter a serious difficulty. If 
either the nature of the metal or the temperature changes from one 
section of the cireuit to the next, we can still easily conceive a state 
of things in which there is nowhere a continual increase of positive 
or negative electric charge; this requires only that the fofa/ electric 
current be O for every section of an open circuit and that it have the 
same intensity for every section of a closed one. But, unless we 
introduce rather artificial hypotheses, it will in general be found 
impossible to make each partial current, i.e. the current due to each 
kind of electrons considered by itself, have the same property. The 
consequence will be that the number of positive as well as that of 
negative electrons will increase in some places and diminish in others, 
the change being the same for the two kinds, so that we may speak 
of an accumulation of “neutral electricity” in some points and of a 
diminution of the quantity of neutral electricity in others. Now, 
supposing all observable properties to remain stationary, as indeed 
they may, we must of necessity suppose that a volume-element 
of the metal contains at each instant the same number of really 
free electrons. This may be brought about in two ways. We may 
in the first place imagine that all electrons above the normal number 
that are introduced into the element are immediately caught by the 
metallic atoms and fixed to them, and that, on the other hand, in 
47% 
