Nice short piece on a key element of Adam Smith's Wealth of Nations, here!

When I read The Wealth of Nations I was struck by the fluid mechanical nature of Smith’s material analogies - the places he describes different channels for money and goods to flow like those channels really are canals with flow rates and flow height levels.

This connects to what was an extremely important part of Newton’s legacy in British science, for instance in “Newtonian medicine” which focused on the hydraulics of blood above all, though this hydraulic Newtonianism became unfashionable and is not so well remembered today as Newton's gravitational theory (and I Bernard Cohen made an interesting case that for American science, it was the Opticks that really inspired Ben Franklin and his peers, not gravity or hydraulics: there were several separate Newtonian traditions).

Therefore when I read the Wealth of Nations it was striking to me how much Smith's model was a *steady state hydraulic flow* model rather than an equilibrium model, which is in a way far ahead of its time since modern thermodynamics has only recently been recognizing the deep formal similarities of the mathematics of stochastic equilibria and stochastic steady states through work like Crooks‘s and Jarzynski’s. The principle of locality of fluid mechanics (no fluid particle of a river “knows it is flowing to the ocean” yet it flows there nonetheless through its local laws of motion) is a clear scientific analog to Smith's principle of economic locality here, well-highlighted in Nik's article.