Far Eastern and Russian Institute, not dated===On Wittfogel===*G. L. Ulmen, "The Science of Society, Towards an Understanding of the Life and Work of Karl August Wittfogel", Mouton, The Hague, 1978*G. L. Ulmen, ed., "Society and History, Essays in Honor of Karl August Wittfogel", Mouton, The Hague, 1978, ISBN 90-279-7776-3* "Karl A. Wittfogel," George Taylor, International Encyclopedia of Social Sciences, 18 (London: Collier, 1979), p. 812.
Amerikanischer Sketch" (The Skyscraper), Malik, 1924* G. L. Ulmen, "The Science of Society, Towards an Understanding of the Life and Work of Karl August Wittfogel", Mouton, The Hague, 1978* G. L. Ulmen, ed., "Society and History, Essays in Honor of Karl August Wittfogel", Mouton, The Hague, 1978, ISBN 90-279-7776-3* "Karl A. Wittfogel, " George Taylor, International Encyclopedia of Social Sciences, 18 (London: Collier, 1979), p. 812.