The velocity potential of a harmonic oscillating ‡uid in the x-direction is given by © = Ux¢cos!t. If the magnitude of the potential © - the potential value - will be doubled, then the velocity component will be doubled too; u = d©=dx = U ¢cos!t. This follows directly from the de…nition of the phenomenon ”potential”, so the potential has been described by a linear function. This means also that all potential ‡ow elements (pulsating uniform ‡ows, sources, sinks, etc.) may be superposed.