Series Is Presented Here As Two Variables--(1)--Original Data, 1948-1961 (2)--Original Data, 1959-1968. Source: Data For 1948-1960: U.S. Bureau Of The Census, Business Cycle Developments, July 1964. Data For 1961: Secured By Phone Direct From The First National City Bank On December 1, 1964.
This NBER data series m13047a appears on the NBER website in Chapter 13 at http://www.nber.org/databases/macrohistory/contents/chapter13.html.
NBER Indicator: m13047a
Release: NBER Macrohistory Database
National Bureau of Economic Research, Yield On New Issues of High-Grade Corporate Bonds, First National City Bank for United States [M1347AUSM156NNBR], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/M1347AUSM156NNBR/, October 13, 2015.