1. Clark, Colin, The Conditions ofEconomic Progress (London: MacmillanCo., 1940), pp. 148-149.Clark148The Conditions of Economic Progress1940
2. Cuber, John F., Sociology: A Synop-sis of Principles (N. Y.: Appleton-Century-Crafts, Inc., 1955 edit.), pp.413-418.Cuber413Sociology: A Synopsis of Principles1955