Source: P.H. Douglas: For 1890-1926, "Real Wages In The United States, " P. 96; For 1927-1928, "The Movement Of Money And Real Earnings, " P. 32 (University Of Chicago, Studies In Business Administration, No. 3).
This NBER data series a08053 appears on the NBER website in Chapter 8 at http://www.nber.org/databases/macrohistory/contents/chapter08.html.
NBER Indicator: a08053
Release: NBER Macrohistory Database
National Bureau of Economic Research, Average Hourly Money Earning In Metal Trades for United States [A08053USA052NNBR], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/A08053USA052NNBR/, November 27, 2015.