Two stimulating and innovative papers by Morrill were concerned with waves of spatial diffusion.(Morrill,[1, 2 )The purpose of the first was to propose some insights and interpretations which can be obtained by characteriz ive-like phend Morrill scopic and theoretical implications of such a conceptualization. He was concerned with both time and distance, and noted that in earlier conceptualizations more emphasis had been placed on de ecay re elated to time than on that related to distance. He therefore hypothesized that the number of innovations would de-
