Joan’s voices and visions have played many tricks with her reputation. They have been held to prove that she was mad, that she was a liar and imposter, that she was a sorceress (she was burnt for this), and finally that she was a saint. They do not prove any of these things; but the variety of the conclusions reached shew how little our matter-of-fact historians know about other people’s minds, or even about their own. There are people in the world whose imagination is so vivid that when they have an idea it comes to them as an audible voice, sometimes uttered by a visible figure. Criminal lunatic asylums are occupied largely by murderers who have obeyed voices. Thus a woman may hear voices telling her that she must cut her husband’s throat and strangle her child as they lie asleep; and she may feel obliged to do what she is told. By a medico-legal superstition it is held in our courts that criminals whose temptations present themselves under these illusions are not responsible for their actions, and must be treated as insane. But the seers of visions and the hearers of revelations are not always criminals. The inspirations and intuitions and unconsciously reasoned conclusions of genius sometimes assume similar illusions. Socrates, Luther, Swedenborg, Blake saw visions and heard voices just as Saint Francis and Saint Joan did. If Newton’s imagination had been of the same vividly dramatic kind he might have seen the ghost of Pythagoras walk into the orchard and explain why the apples were falling. Such an illusion would have invalidated neither the theory of gravitation nor Newton’s general sanity. What is more, the visionary method of making the discovery would not be a whit more miraculous than the normal method. The test of sanity is not the normality of the method but the reasonableness of the discovery. If Newton had been informed by Pythagoras that the moon was made of green cheese, then Newton would have been locked up. Gravitation, being a reasoned hypothesis which fitted remarkably well into the Copernican version of the observed physical facts of the universe, established Newton’s reputation for extraordinary intelligence, and would have done so no matter how fantastically he had arrived at it. Yet his theory of gravitation is not so impressive a mental feat as his astounding chronology, which establishes him as the king of mental conjurors, but a Bedlamite king whose authority no one now accepts. On the subject of the eleventh horn of the beast seen by the prophet Daniel he was more fantastic than Joan, because his imagination was not dramatic but mathematical and therefore extraordinarily susceptible to numbers: indeed if all his works were lost except his chronology we should say that he was as mad as a hatter. As it is, who dares diagnose Newton as a madman?