Free exchange | Petty impressive

摘要

William petty was an innovation machine. He designed an early form of catamaran, conceived of a mechanical grain planter, proposed attaching engines to boats and patented a "double-writing" instrument (it produced an extra copy of whatever a writer put down on paper). Petty, who died at Christmas in 1687, was also an innovator in the world of theories. By tinkering with data and simple models, this little-known Englishman came up with many of the ideas-how to measure gdp, why the money supply and banks matter, how lasting unemployment affects the economy-that form the bedrock of modern economics.