Source: The Volume Of Corporate Bond Financing Since 1900 (NBER), W. Braddock Hickman, 1953, Pp. 310 311
This NBER data series q10086 appears on the NBER website in Chapter 10 at http://www.nber.org/databases/macrohistory/contents/chapter10.html.
NBER Indicator: q10086
Release: NBER Macrohistory Database
National Bureau of Economic Research, Bonds Outstanding, Straight Corporate, Par Value, Railroads for United States [Q10086USQ311NNBR], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/Q10086USQ311NNBR/, August 30, 2015.