Source: P.H. Douglas, "Real Wages In The United States, 1890-1926", P. 96.
This NBER data series a08052 appears on the NBER website in Chapter 8 at http://www.nber.org/databases/macrohistory/contents/chapter08.html.
NBER Indicator: a08052
Release: NBER Macrohistory Database
National Bureau of Economic Research, Average Hourly Earnings In Planing Mills for United States [A08052USA052NNBR], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/A08052USA052NNBR/, October 9, 2015.