"Nobel Prize-winning British physicist Paul Dirac was notoriously taciturn. This began early. When Dirac was a child, his authoritarian father, a teacher of French, enforced a rule that Dirac speak to him only in French, as a device to encourage him to learn the language. But since young Dirac had difficulty expressing himself in French, the result was he spoke very little. During the question period after a lecture he gave at the University of Toronto, a member of the audience remarked that he hadn't understood part of a derivation. There followed a long and increasingly awkward silence. When the host finally prodded him to respond, Dirac simply said, "That was a statement, not a question." Dirac's colleagues in Cambridge jokingly defined a unit called a "dirac", which was one word per hour."