AOG Mr. W. Sutherland on the 
investigation on ‘ Ionization, Ionic Velocities, and Atomic 
Sizes” (Phil. Mag. Feb. 1902). It was there shown that if 
a, and a, are the radii, and K, and K, the dielectric capa- 
cities of the two atoms of a binary electrolyte forming a very 
dilute solution in water (m gramme-equivalents per litre) of 
viscosity 7 and dielectric capacitv Ky the current per em.’ in 
the solution due to a rate of fall of potential dE/dx is for 
ionization 2 
Be Lis Seige Ko 1 ae di 
C=10-4mie ae ee a8 eae (9) 
This expression is derived on the usual supposition that in 
electrolytic conduction the atom of an ion simply carries its 
electron from one electrode to the other. But the same 
reasoning if not supplemented by a further principle would 
make the work done in carrying an electron e in an atom of 
dielectric capacity K down a step of potential E,— EK, to be 
Kye(H,—H,)/K, whereas it is in reality e(E,—H,). It was 
therefore pointed out that the electrolytic current cannot 
consist solely of the waftage of electrons by atoms. The 
further principle necessary to make equation (9) consistent 
with the conservation of energy can be ascertained by con- 
sidering the following very simple case. A unit charge of 
electricity is placed inside a very thin slab of dielectric 
capacity K between two plates at potentials H, and Hy, at 
distance D apart in vacuum and parallel to them. The 
force acting on the charge is (H,—E,)/DK according to 
usual electrostatic principles, and the work done in moving 
the charge inclosed by dielectric of capacity K from the one 
plate to the other is (E,—E,)/K. But, on the contrary, we 
know that this work must be H,—E,. Evidently, then, 
(E,—E,)/K is not a full determination of the work involved. 
It gives the work due to a certain displacement of the unit 
charge relative to the matter of the two plates. But there 
has been also a displacement of the ether relative to the two 
plates. If the displacement of the ether is written down as 
D(1—1/K), and the force producing this is taken to be 
(H,—H,)/D, the force anywhere between the two plates 
except in the dielectric slab, then the work due to ether dis- 
placement is (H,;—E,)(1—1/K), which when added to the 
work for displacement relative to matter gives the whole 
work H,— Ep. 
Now the expression D(1—1/K) for the displacement of 
the ether is just what is required by Fresnel’s theory that 
the velocity of the ether in a moving transparent body is 
