Two Out Of Three Months Used In Computing Trough. Source: The Volume Of Corporate Bond Financing Since 1900, W. Braddock Hickman, A Study By The National Bureau Of Economic Research, Princeton University Press, 1953, Pp. 324-325, Appendix A, Table A-15.
This NBER data series m10071 appears on the NBER website in Chapter 10 at http://www.nber.org/databases/macrohistory/contents/chapter10.html.
NBER Indicator: m10071
Release: NBER Macrohistory Database
National Bureau of Economic Research, Bond Offerings, Par Value, All Industries for United States [M10071USM311NNBR], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/M10071USM311NNBR/, July 30, 2015.