Lord Rayleigh has pointed out that all theories are defective in that they disregard the fact that one at least of the media is dispersive, and that it is probable that finite reflection would result at the **interface** of media of different dispersive powers, even in the case of waves for which the refractive indices are absolutely the same.

If T12 denote the interfacial tension, the energy corresponding to unit of area of the **interface** b Q FIG.

For instance, if T31> T12+ T23, the second fluid spreads itself indefinitely upon the **interface** of the first and third fluids.

On the analogy between this case and that of the **interface** between two solutions, Nernst has arrived at similar logarithmic expressions for the difference of potential, which becomes proportional to log (P 1 /P 2) where P2 is taken to mean the osmotic pressure of the cations in the solution, and P i the osmotic pressure of the cations in the substance of the metal itself.