It is readily seen that the two differential equationswhich play an important rôle in Professor Chrystal's mathematical theory of the Seiches, are special cases of the more general typeWith regard to the first, the Seiche-equation, this becomes at once apparent by writing a= − ½. Equation (2), on the other hand, which we may briefly call the Stokes equation [see Professor Chrystal's paper on "Some further Results in the Mathematical Theory of Seiches,"Proc. Roy. Soc. Edin., vol. xxv.] will be

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... cognised as a special case (a = + 1) of the equationwhich is transformed into (3) by the substitution.