The one-dimensional motion of an electron gas in a regular and infinite ion-grid is described by the development in time of the disturbance f(v,t)eikz of the distribution function. The Fourier transform of f with respect to v is shown to develop in time like a wave propagating towards infinity with velocity k in the transform space. The wave form and its distortion are governed by a function D closely related to the Fourier transform of the undisturbed velocity distribution. For kvt‹‹ωp there is in addition a standing wave oscillating with the plasma frequency ωp (vt=thermal velocity).