When I said above that I believed in witches, but not in witch-smellers, I stated my full position about that conception of heredity, that half-formed philosophy of fears and omens; of curses and weird recurrence and darkness and the doom of blood, which, as preached to humanity to-day, is often more inhuman than witchcraft itself. I do not deny that this dark element exists; I only affirm that it is dark; or, in other words, that its most strenuous students are evidently in the dark about it. I would no more trust Dr. Karl Pearson on a heredity-hunt than on a heresy-hunt. I am perfectly ready to give my reasons for thinking this; and I believe any well-balanced person, if he reflects on them, will think as I do. There are two senses in which a man may be said to know or not know a subject. I know the subject of arithmetic, for instance; that is, I am not good at it, but I know what it is. I am sufficiently familiar with its use to see the absurdity of anyone who says, "So vulgar a fraction cannot be mentioned before ladies," or "This unit is Unionist, I hope." Considering myself for one moment as an arithmetician, I may say that I know next to nothing about my subject: but I know my subject. I know it in the street. There is the other kind of man, like Dr. Karl Pearson, who undoubtedly knows a vast amount about his subject; who undoubtedly lives in great forests of facts concerning kinship and inheritance. But it is not, by any means, the same thing to have searched the forests and to have recognised the frontiers. Indeed, the two things generally belong to two very different types of mind. I gravely doubt whether the Astronomer-Royal would write the best essay on the relations between astronomy and astrology. I doubt whether the President of the Geographical Society could give the best definition and history of the words "geography" and "geology."