J. Bradford DeLong (1992), "Productivity and Machinery Investment: A Long Run Look 1870-1980"
J. Bradford DeLong (1992), "Productivity and Machinery Investment: A Long Run Look 1870-1980," Journal of Economic History 53: 2 (June), 307-24.
http://www.j-bradford-delong.net/pdf_files/JEH_Machinery.pdf