¹ The only substantial change in area since the Mexican War settlement was the Gadsden Purchase of 1853, which contributed a little less than one per cent in area and practically no population.

² This procedure has already been used by P. Sargant Florence and Arthur J. Wensley in measuring the degree of localization of individual manufacturing industries in Great Britain (see Political and Economic Planning [PEP], The Location of Industry in Great Britain [London, 1939Google Scholar, Appendix II]), and has been applied by Professor Florence to American data in a forthcoming study of Industrial Location and National Policy by the National Resources Planning Board. Some other measures applicable to the purpose here in hand are discussed in Wright, John K., “Some Measures of Distributions,” in Annals of the Association of American Geographers, December, 1937Google Scholar, and in my article, “The Measurement of Industrial Localization,” in Review of Economic Statistics, November, 1936.

³ Possibly an illuminating way of interpreting this coefficient is to say that it indicates what percentage of the total population would have to move across State lines in order to make the average density of population the same in all States.

⁴ It will be noted that the coefficient for the total population is by no means always intermediate in value between that for the whites and that for the Negroes. The relation depends upon the direction and amount of correlation between the shifts of the Negro and white groups.