Page:Proceedings of the Royal Society of London Vol 60.djvu/359

332 Hermann has passed oyer C, and omitted to take W into account, confining himself to the theoretical relation between Q* and P*. But we know very little about polarisation, save in the case of solid electrodes. The term polarisation, as frequently used, includes two phenomena, which ought to be kept distinct, viz.:—

(а) That condition of the interface between two conductors, of which one at least is an electrolyte, in which the molecules are under a stress not greater than they are capable of supporting without chemical change.

(b) A deposit upon the surface of a solid, or in the contiguous liquid, of the products of actual electrolysis.

If one of the conductors is a solid, the inevitable local differences of condition or of composition enable actual electrolysis to take place, even with a P.D. smaller than that proper to the chemical change implied.

But if both conductors are liquid and perfectly pure, the stress is so far equalised' that no electrolysis is possible until the E.M.P. reaches a certain value, more sharply defined in proportion as the materials are pure.

I hold that with differences of potential which do not reach this limit, the electromotive force is transmuted without electrolysis into mechanical force, and manifests itself as kinetic energy, until by the motion of the meniscus it becomes transformed into potential energy.

The locus of transformation from electrical to mechanical force must clearly be the two interfaces mercury-acid and acid-mercnry, and it is upon these that the stress acts. The resistance is distributed along the tube, and is partly electrical, but to a far larger extent mechanical.

Is it reasonable, therefore, to assume that the sole cause of delay is the “ Polarisations-geschwindigkeit ” of the meniscus ?

I believe that in the case of an interface between two liquids, the rate of polarisation is to be measured in terms o£ the vibration-period of a molecule, rather than in decimals of a second.

Actual electrolysis is another matter, and I hold that it does not take place in a properly working electrometer. We do not assume electrolysis when two pith balls repel each other after receiving a charge, nor when a closed coil is slipped over a magnet. But the coil cannot be got off again, nor can the balls fall together without the generation somewhere of a current. I cannot see why we should assume electrolysis in the case of the capillary electrometer. The marvellous rapidity of the action to which I have not yet found a limit, is against it, as is also the fact that the substitution for the acid, or the addition to it, of any substance which can be electrolysed by a smaller electromotive force, reduces the range of potential difference for which it can be used.