It is not enough to say, that, after the fact, you can understand partially how Mahometanism came to be. All historians worth the name have told us something about that. But when we talk of science, we mean something with more ambitious pretences, we mean something which can foresee as well as explain; and, thus looked at, to state the problem is to show its absurdity. As little could the wisest man have foreseen this mighty revolution, as thirty years ago such a thing as Mormonism could have been anticipated in America; as little as it could have been foreseen that table-turning and spirit-rapping would have been an outcome of the scientific culture of England in the nineteenth century. The greatest of Roman thinkers, gazing mournfully at the seething mass of moral putrefaction round him, detected and deigned to notice among its elements a certain detestable superstition, so he called it, rising up amidst the offscouring of the Jews, which was named Christianity. Could Tacitus have looked forward nine centuries to the Rome of Gregory VII., could he have beheld the representative of the majesty of the Caesars holding the stirrup of the Pontiff of that vile and execrated sect, the spectacle would scarcely have appeared to him the fulfilment of a rational expectation, or an intelligible result of the causes in operation round him. Tacitus, indeed, was born before the science of history; but would M. Comte have seen any more clearly? Nor is the case much better if we are less hard upon our philosophy; if we content ourselves with the past, and require only a scientific explanation of that. First, for the facts themselves. They come to us through the minds of those who recorded them, neither machines nor angels, but fallible creatures, with human passions and prejudices. Tacitus and Thucydides were perhaps the ablest men who ever gave themselves to writing history; the ablest, and also the most incapable of conscious falsehood. Yet even now, after all these centuries, the truth of what they relate is called in question. Good reasons can be given to show that neither of them can be confidently trusted. If we doubt with these, whom are we to believe? Or again, let the facts be granted. To revert to my simile of the box of letters, you have but to select such facts as suit you, you have but to leave alone those which do not suit you, and let your theory of history be what it will, you can find no difficulty in providing facts to prove it.