I'm not sure whether this question suits this website, however, I don't know where else I could ask it. It is no mathematical problem or something similar, still I hope it won't be closed.
A few weeks ago, our assistant professor in physics told us a story about Maxwell when we came to speak about Maxwell's equations. He said rumour has it that once in an exam, Maxwell faced a differential equation or integral - at that time thought unsolvable - and solved it.
I wonder whether there are more famous rumours or anecdotes about mathematicians or physicists (and which of them are true and which not). I believe everyone knows the story of how Gauss computed
$$\sum_{n=1}^{100} n$$
an exercise his teacher gave to his class to keep it busy. Or a more famous example: Everyone knows how Newton discovered gravity (is that one actually true?). Or how Archimedes found Archimedes' principle. So, to put it into a single line:
Do you know any other noteworthy anecdotes about famous mathematicians or physicists?
EDIT: In case you provide an answer, please also state whether the anecdote is true or not, if possible. Thanks a lot for the hitherto existing answers!
E.T. Bell's classic book Men of Mathematics has many anecdotes about famous mathematicians, although it is (I think) sometimes thought less of because it is not 100% accurate about everything. It's certainly a very entertaining book.