Romeo Vitelli in Providentia:
As one of the leading French mathematicians of his generation and author of two books on elementary geometry, Jacques Hadamard was always open to new mathematical ideas. When he received a mathematical proof in the mail from a previously unknown mathematician named Andre Bloch, Hadamard was mesmerized by its elegance. The proof related to a branch of elementary geometry involving paratactic circles, systems of two circles with orthogonal planes with the intersection being the common diameter of the two circles and cut according to a harmonic division. According to Bloch, parataxy remained invariant under inversion and any inversion with respect to a point situated on one of them transforms them into a circle and it's axis.
Hadamard was so intrigued by Bloch's discovery that he immediately decided to invite him to dinner. Since he had no other way of contacting Bloch, Hadamard wrote to the return address of 57 Grand Rue, Saint-Maurice with the invitation. Bloch wrote back that a visit would be impossible but asked the great mathematician to visit him instead. It was only when Jacques Hadamard finally took him up on his offer that he discovered why Bloch was unable to come to him: 57 Grand Rue, Saint-Maurice was the address of the Charenton lunatic asylum (now the Esquiral hospital) where Andre Bloch was an inmate. He had been involuntarily committed to the hospital following a brutal triple murder in 1917 and would never be allowed to leave. Although Hadamard was astonished by his discovery, he and Bloch talked at length about mathematics and he learned more about the inmate's story.