Grahn, E. “Die städtischen Wasserwerke,” in Wuttke, _Die Deutschen Städte_ (Leipzig, 1904), pp. 301–44. A statement of the water-supply problem in German cities. Höffner, C. “Die Gaswerke,” in Wuttke, _Die Deutschen Städte_ (Leipzig, 1904), pp. 198–238. A statement of the evolution and present status of the technique of gas supply in the modern city. Jephson, H. L. _The Sanitary Evolution of London_ (London, 1907). (VI.) Kübler, Wilhelm. “Über städtische Elektrizitätswerke,” in Wuttke, _Die Deutschen Städte_, pp. 239–300. An account of the municipal electricity works in German cities. Most books on the modern city contain a chapter on public utilities, and a great many technical journals and municipal reports are accessible giving detailed accounts of various aspects of both the technical, the administrative, and the functional sides of the public utility situation. 2. One of the most characteristic features of city life is the high degree of intercommunication. This is made possible by technical devices, such as the telephone, street cars, and the automobile. While the sociologist has no intrinsic interest in these technical devices, they become an object of study as factors entering, for instance, into the problem of mobility of the city population. D’Avenel, G. le Vicomte. _Le Mécanisme de la Vie moderne_ (3 vols.; Paris, 1922). Among many other aspects of the city as a physical mechanism, has a chapter on publicity, urban transportation, and communication. This work has gone through many editions and is written in a popular style. (VI; IX, 1.) Harris, Emerson Pitt. _The Community Newspaper_ (New York, 1923). (IX, 3.) Kingsbury, J. E. _The Telephone and Telephone Exchanges: Their Invention and Development_ (London and New York, 1915). Lewis, H. M., and Goodrich, E. P. _Highway Traffic in New York and Its Environs_ (New York, 1924). The results of a study embodied in a report for the Committee on a Regional Plan for New York and its Environs. (IV, 2; V, 4, 5; VI, 2; VII, 2, 4.) Park, Robert E. _The Immigrant Press and Its Control_ (New York, 1922). A study of the organization and the influence of the press in the immigrant communities of the large city (IX, 3.) The municipal transportation and communication question has developed a large literature which is to be found in many separate works on the telephone, telegraph, radio, street-car systems, busses, automobile, mail service, newspaper, and railways as well as in municipal reports, technical and administrative journals, and textbooks on the city. 3. The existence of streets, pavement, alleys, sewers, and other devices of the same sort that characterize the city as a physical mechanism influence the behavior of the person and the group, and as such are of interest to the sociologist.