The period since 1870 has an important unifying characteristic in that throughout these eig as been response to the complex of cumulative forces which we generally call industrialization. It is quite clear, however, that 1870 was not the be- ginning of the process of industrialization in this country. The propor- tion of gainful workers in agriculture fell from 71 per cent in 1820 to 64 per cent in 1850. It fell another 10 percentage points by 1870 Steam transport by water and rail was already common when the period begins. The proportion of the gainfully employed engaged in manufacturing and construction rose from 12 to 21 per cent between 1820 and 1870. Real per capita output rose significantly during the 1850s. It was set back by the Civil War, but aggregate output well nigh doubled from 1850 to 1870. The data before 1870--and still more before 1850-are highly dubious, but it seems clear that the period since 1870 does not include the entire era of industrialization and rapid income rise in this country. We are, in an important sense, dealing with a period arbitrarily delimited by the availability of fairly reliable com- prehensive figures It may be of some use if i try to state at the very beginning the three ain conclusions of my paper. First, between the decade 1869-78 and the decade 1944-53, net national product per capita in constant prices pproximately quadrupled, while population more than tripled. The source of the great increase in net product per head was not mainly an increase in labor input per head, not even an increase in capital per head, as these resource elements are conventionally conceived and measured. Its source must be sought principally in the complex of tle understood forces which caused productivity, that is, output per unit of utilized resources, to rise. Second, it is not clear that there has been any significant trend in the rates of growth of total output and of output per head. It is true that national product estimates, on their face, suggest some decline in the rates of growth--somewhat more clearly for total output; some what less clearly for output per capita. It is doubtful, however, whether the data can be accepted with confidence for this purpose and still more doubtful whether the apparent retardation in growth, such as it is, rep- resents the effect of persistent forces. Insofar le can observe a de- cline in the rate of growth, its source is not in the productivity of re sources, which has continued to grow at a steady, perhaps an accelerat- These are W. I. Kings d Income of the People of the United g-Term Chang Sim by Simon Kuznets, Cambridge, Bowes es,1952,p.240)