There were about 17 times as many Negroes in the United States in 1940 as there were in 1790, when the first census was taken, but in the same period the white population increased 37 times (Figure 1). Negroes were 19.3 per cent of the American population in 1790, but only 9.8 per cent in 1940. Except for the first decade in the nineteenth century and the 1930’s, this proportion has been steadily declining. The trend in the proportion has been governed by the natural increase of the two population stocks, by expansion of the territorial limits of the United States and by immigration. Since all figures on these things are uncertain, it is not possible to make an accurate imputation of the changes in the relative importance of these factors. Since descendants of immigrants after the second generation are included in the category of “native born,” it is still less possible to calculate what the proportion of Negroes would have been had there been no immigration of either race to the United States after 1790.