The American economist Irving Fisher (1867-1947) made significant and original contributions in the fields of economics, mathematics, statistics, demography, public health and sanitation, and public affairs.

Irving Fisher was born in Saugerties, N.Y., on Feb. 27, 1867. He received his doctoral degree in mathematics at Yale in 1891. From 1892 until 1895 he taught mathematics at Yale; in 1895 he joined the faculty of political economy, where he remained until his retirement as professor emeritus in 1935.

It is virtually impossible to do justice to Fisher's many contributions to economics and statistics, but his writings on monetary theory and policy and index numbers have earned special acclaim. He brought to his writings the lucidity, analytical precision, and rigor of an accomplished mathematician. In The Purchasing Power of Money (1911) Fisher completely recast the theory of money into his classical quantity-theory-of-money equation MV + M'V' = PQ, which made the purchasing power of money (or its reciprocal, the...