In an article named Conversation with Vladimir Igorevich Arnol'd, Arnol'd said
I will state another problem mentioned there, this one variational, on the solid of revolution with least resistance under motion along its axis in a very rarified medium. Here Newton was 300 years ahead of his time: the extremum is not smooth, but has a break, and Newton knew about it. As V. M. Tikhomirov has informed me, this break appears in Newton's picture, but is absent from the picture in some later editions of the Principia
Is that true? Which edition of Newton's Principia and where does this picture appear?