My article on Prussian public finance in the December 1966 issue of this Journal contained some errors of calculation which partially affect the arguments I advanced there and which provide an excellent object lesson in the hasty use of quantitative evidence. After unaccountably converting current prices into constant ones by multiplication instead of division, I rushed the results off to the editors without checking them.

In his most enlightening paper on Federal Reserve policy in 1920–1921 Elmus Wicker's statement on the Bank of England's policies is not strictly in accord with the facts.

The English system of no legal reserve requirements imparted a greater degree of flexibility to the monetary authorities and allowed a greater economy in the use of the gold reserve. The entire gold reserve was available in emergencies to safeguard the pound.

Shipping tonnages have been frequently used as a basis for inquiries covering a wide and increasing range of topics in economic history. For example, industry studies, descriptions of shipping routes and trade flows, colonial balance of payments estimates, and an analysis of the sources of productivity change in shipping have all been based–at least in part–on tonnage figures. A major problem in using tonnages as a means of historical quantification is that the term “ton” (either a shipping ton or a commodity ton) has varied substantially over time. This is especially true for the Colonial Period, when it was defined differently depending on its usage or the agent or the country reporting it. Fortunately, several recent research efforts have greatly improved our understanding of the meaning and limitations of historical tonnages.

Every economist must be pleased to start some hares; it can become embarrassing, however, when they begin to breed like rabbits. In the ten years since we first tried our slavery model in public, in Professor Gerschenkron's history seminar, more than thirty published arguments addressed to that model have come to our attention. We don't pretend to know whether that represents an increased output over preceding decades. Besides, in our youthful enthusiasm we gave the impression that we were disposing, once and for all, of a piece of intellectual game that was already rather high. In any event, the apparent egocentricity that turned up all those papers and articles may be explained, if not justified, by Ralph Barton Perry's dictum that every reader looks up two references in an index: sex, and his own name.

The story is told that Dean Donham of the Harvard Business School once asked Professor Schumpeter, after a lecture on the entrepreneur—Schumpeter's plumed knight of economic development–what was the most important single factor in accounting for the success of the businessman. Quick as a shot came the answer: “Good health.” For purposes of this inquiry into certain aspects of American social structure and American values which seem to have been of decisive importance in contributing to American economic growth, certain variables–like the health of the businessman and the endowment of the country with respect to natural resources –will not be considered.

The current controversies about production and yields of medieval agriculture may give an outsider the impression that on this subject historians are more at variance than they actually are. Some historians may still cling to the Victorian belief that things economic were perpetually on the rise; historians thus minded are inclined to take it for granted that both the aggregate product of agriculture and agricultural output per head improved all through the Middle Ages. Other students, for example, Beveridge or Bennett, derived from the imperfectly selected data of the Bishop of Winchester's manors the impression that output per acre, and probably also per unit of seed, stayed put all through the Middle Ages. More recently other historians, including myself, have argued that output per acre tended to slump in the earlier, that is, pre-Black Death period, and may have picked up somewhat in the late fourteenth and fifteenth centuries. The concert of historians may therefore strike the ear as being even more cacophonous on this theme than on most other medieval themes.