Source: The Economist (London)
This NBER data series m03033b appears on the NBER website in Chapter 3 at http://www.nber.org/databases/macrohistory/contents/chapter03.html.
NBER Indicator: m03033b
Release: NBER Macrohistory Database
National Bureau of Economic Research, Index of Shipping Freight Rates, British Routes for Great Britain [M0333BGBM316SNBR], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/M0333BGBM316SNBR/, September 2, 2015.