Where, then, I ask, in all the teaching of Nature’s school, has there been more of illusion than in her lessons of astronomy? When I was a boy, I remember, in the midst of a hateful sum of long division that would not come out right, devoting my attention to the sun moving through the branches of certain trees, and announcing to my tutor that “The sun moves.” “No, you are mistaken.” “But I cannot be mistaken, for I saw it.” I rivalled—I exceeded—the obstinacy of Galileo; I was ready to be punished rather than consent to say what seemed to me a manifest falsehood, that the sun did not move. Surely this boyish experience represents the experience of mankind, except that the tutor who has corrected their astronomical illusions, has been their own long, very long experience. Does it not seem sometimes as if God Himself had said, when He made the heavens to declare His glory, “Being what they are, my children must be led to knowledge through error, to truth through illusion”? It may be said that in some cases men have fallen into astronomical mistakes through their own fault; through haste, for example, through the love of neat and complete theories, through carelessness, through excessive regard for authority; and so indeed they have. But is it always so? When you and I last walked out together on Hampstead Heath, you took out your watch, as the sun went down over Harrow, and said, “Now he’s gone, and it’s just eight.” I remember replying to you, “So it seems; but of course you know he ‘went’ more than eight minutes ago.” You stared, and I said no more; for something else diverted your attention at the time, and I felt I had been guilty of a little bit of pedantry. But I said quietly to myself as we went down the hill, “I don’t suppose he knows it, but the sun certainly ‘went’ eight minutes ago; and what my young friend saw was an image of the sun raised by the refraction of the mist, like the image of a penny seen in a basin of water.” Well now, was this your fault, this error of yours? No, it was, in the second place, the fault of the University of Oxford, which has bribed the schools to desist from teaching mathematics to any boy with a taste for classics and literature, so that you had to give up your mathematical studies before you came to optics; and it was, in the first place, the fault of—what shall I say? Shall I say the fault of Nature? That means the fault of God. Say, if you like, that it was the fault of Matter, or of an Evil principle. Say, it was no one’s fault. Say that more good than harm results from it, in the way of stimulating thought and research. Deny it was a fault at all. Yet do not deny that it represents a Law, the Law of the attainment of truth through illusion—a Law which it is folly to ignore.