Measurements of the spatial dependence of the zero power transfer function of the reactor NORA have been performed, using a local reactivity perturbation. Spatial effects were observed for frequencies higher than the break frequency β/l, and the wave nature of the flux space-time variation has been recognized. A theoretical interpretation based on two-group diffusion theory is given by solution of the equations by the finite difference method on an analogue computer. The qualitative agreement between theory and experiment is good.