Tic-tac geometry: A theorem in full swing

When the French mathematician Michel Chasles expressed his ‘principle of correspondence’ in 1864, he claimed to have obtained a theorem from which one could derive a general and systematic method for the effortless obtention of an infinity of geometrical propositions. And yet, barely two decades later, this very theorem was widely regarded as a boring or uninteresting result, whose teaching in universities might ingrain noxious mathematical habits in the minds of young students. In this article, Nicolas Michel uses the principle of correspondence as an example to show how different social contexts for the practice and teaching of science shaped different ways of valuing and measuring the worth of a result.