“It is assumed that the reader is familiar with some, at least, of the various conceptions of the business cycle currently discussed by economists. These are summarized, in greater detail than is necessary for our present purposes, in Mitchell's "Business Cycles, The Problem and the Setting" (1927), and King's "The Cause of Economic Fluctuations" (1938); the latter being noteworthy for its sympathetic reference to those who have found it necessary to push their search for the underlying causes of business cycles beyond the limits customarily regarded as the boundaries of the economic field.”