The well-known expression for the total cross section in terms of the imaginary part of the coherent forward scattered amplitude is derived in a simple and general way from wave theory. The derivation also shows that there is a “;shadow remnant”; beyond the actual shadow, within which the forward coherent scattering intensity is diminished, of approximate radius (r/k)1/2, where r is the distance from the scattering center and k=2π/λ is the wave number. A qualitative understanding of the shadow remnant is obtained in terms of the uncertainty principle.