520 
PROFESSOR J. J. THOMSON ON SOME APPLICATIONS OF 
break up independently of the electric field, then these inter-atomic or inter-molecular 
forces would be absent, and the atoms or molecules would be free to arrange them¬ 
selves so as to diminish the potential energy due to the electric field. This diminution 
in the electrical energy would be equivalent to a discharge of the electric field, partial 
or total, according as the energy is only partially or totally exhausted. According to 
this view, the electric current is a discontinuous phenomenon, though there need not 
be anything corresponding to a definite period, as the field may not be simultaneously 
discharged at all points. We may suppose that much the same kind of thing occurs 
in electrolytes, and in this case the view has much in common with the Wllliamson- 
Clausius hypothesis. According to this view the electrolyte is not decomposed by 
the electric field, the function of the electric forces being merely to direct the motion 
of the components of the molecules dissociated by other means. According to our 
view it is the re-arrangement of the components of dissociated molecules or groups of 
molecules which produces the current. This view is in accordance with Faraday’s 
remark that induction always precedes conduction. If, as in the case of the electric 
discharge through permanent gases, the electric field were strong enough to separate 
the molecules without any independent dissociation, we should expect the law con¬ 
necting the current with the electromotive force to be different from the law con¬ 
necting the same quantities when the electromotive force is too weak to decompose 
the molecule. There seems to be evidence for such a difference, for Quincke* has 
shown that when the E.M.F. is very large the current through badly conducting 
liquids, such as olive oil or benzene, does not obey Ohm’s Law, while the experiments 
of Mr. New all and myself have shown that when the E.M.F. is small, not more 
than a few hundred volts per centimetre, the current does obey Ohm’s Law. 
We shall now proceed to endeavour to represent the theory symbolically. To fix 
our ideas, let us consider the case of an air-condenser whose armatures are connected 
with the poles of a battery whose E.M.F. is greater than the air-space can stand: 
then, as soon as the armatures are connected to the poles of the battery, there is an 
electric displacement across the air-space in the direction of the E.M.F. ; then the air 
breaks down, and there is the passage of a quantity of electricity—equal per unit area 
to the displacement across the unit area—from one armature to the other, and then 
the disappearance of the displacement. Now, whether we take the ordinary two-fluid 
theory, or Maxwell’s displacement theory, the result is the same; let us take the 
two-fluid theory first—then the displacements count for nothing, and we have only to 
consider the passage of the electricity across the air-space. Let us next take 
Maxwell’s theory—the effect of the disappearance of the displacement is equal and 
opposite to that of the passage of the electricity across the air-space—so that we are 
left with the effect of the establishment of the displacement, which is the same as 
that of the passage of the electricity, and the two theories lead to identical results; 
and we may conclude that when a field, such that the displacement across unit area 
* ‘Wiedemann’s Annalen,’ vol. 28, p. 529. 
