A summary of the city as a political unit, together with its function from the military standpoint. (II; III, 1, 2, 3, 4; IV, 5.) 3. The statisticians have at various times been forced to define a city because census-taking and interpreting presupposes the existence of definite statistical units. The principal statistical methods of defining the city are: (1) by extent of the area of settlement, and (2) by number of inhabitants. In the history of the United States Census the city has been variously defined as an incorporated community of 8,000 inhabitants or more, then of 4,000, and at the present time of 2,500 inhabitants. Blankenburg, R. “What Is a City?” _Independent_, XXCV (January 17, 1916), 84–85. Meuriot, P. M. G. “Du criterium adopté pour la définition de la population urbaine,” _Soc. de Statist. de Paris_, LV (October, 1914), 418–30. Reuter, E. B. _Population Problems_ (Philadelphia and London, 1924). Shows the changing statistical definitions of the city adopted at various times by the United States Census. Contains a great deal of other material relating to urban population. (VII, 2, 3; VIII, 1, 2.) 4. The economists have been interested in tracing the development of the city as an economic unit. The city, from this standpoint, may be regarded as typical of a certain stage in economic development. The rise of the city is intimately associated with the transition from handicraft to machine industry, the division of labor, the market, and exchange. Besides the great number of economic histories which trace the general movement toward urban economy there are many monographs of special cities whose economic history has been studied, and some instances of present-day developments in metropolitan economy. Below, George von. “Die Entstehung des modernen Kapitalismus und die Hauptstädte,” _Schmollers Jahrbuch_, XLIII (1919), 811–28. (III, 4; IV, 1, 4, 6.) Cheney, Edward Potts. _Industrial and Social History of England_ (New York, 1910). (II, 2, 3; IV, 6.) Day, Clive. _History of Commerce_ (New York, 1920). (II; III, 4; IV, 6.) Dillen, Johannes Gerard van. _Het Economisch karakter der Middeleeuwsche Stad._ I. _De Theorie der gesloten Stad-Huishanding_ (Amsterdam, 1914). (II, 2; III, 4, 5; IV, 6.) Gras, Norman S. B. _An Introduction to Economic History_ (New York, 1922). Considerable material on the rise of the city as an economic unit. (II, 2, 3; III, 4, 5; IV, 1, 2, 6; X, 1.) Sombart, Werner. _The Quintessence of Capitalism: A Study of the History and Psychology of the Modern Business Man._ Translated by M. Epstein (New York, 1915). (II, 3; IV, 6; IX; X; 3.) Waentig, H. “Die wirtschaftliche Bedeutung der Grossstädte,” in the volume, _Die Grossstadt_, edited by Th. Petermann, Dresden, 1903. A thorough study of the increasing significance of the city as an economic unit. (III, 4; IV, 6.)