Group Velocity and Wave Mechanics

Abstract

IF it be true that Nature is built up not of particles but of waves, it is obviously of great importance to gain clear ideas as to the characteristics of wave motion. In dealing with any oscillatory motion, Dr. Albert Campbell suggested several years ago the use of the term pulsatance (an alternative form sometimes used is pulsance) for 2πσ where σ is the frequency (Proc. Phys. Soc., vol. 31, p. 80; 1919). Thus the pulsatance is the number of vibrations in 2π units of time. I have found this term of very great service in teaching, as it economises time in discussion and space in writing or printing. Even the elementary student appreciates its value when he recognises that it corresponds to angular velocity in the reference circle in defining simple harmonic motion. Such a motion is represented by the equation y = A sin pt, where A is the amplitude and p the pulsatance.