Published online by Cambridge University Press: 15 September 2014
§ 1. In a former paper “On Group-Velocity and on the Propagation of Waves in a Dispersive Medium” (Proc. R.S.E., xxix. pp. 445–470, 1909), it was shown that group-velocity, or the principle of “stationary phase,” provides us with a satisfactory explanation of the modus operandi of dispersion; and the principle was applied to obtain an expression for the effect of a single impulse confined to the neighbourhood of a point of the medium. The present paper is intended to fulfil a promise given in § 29 of that paper, to show that by means of this principle we can arrive at the general features of the wave-system in a dispersive medium resulting from any limited initial disturbance.
page 242 note * Boltzmann, Festschrift, 1904.
page 243 note * Proc. Lon. Math. Soc., t. xx., 1888.
page 244 note * See Lord Rayleigh, Phil. Mag., July 1909.
page 245 note * Phil. Mag., vol. xxiii., March 1887.
page 248 note * After this paper had been completed I found this result given in a very comprehensive paper by DrHavelock, T. H., “The Propagation of Groups of Waves in Dispersive Media,” in Proc. Roy. Soc., lxxxi., 1908 Google Scholar, obtained by a similar application of Lord Kelvin's 1887 result to that given in §§ 6, 7 above. The view of group-velocity given in my paper, Proc. R.S.E., 1909, is there fully discussed and illustrated.