It is many years since the first glimmer of the theory which is now almost, if not quite, reduced to fact dawned first on my mind. A somewhat extensive course of miscellaneous and obsolete reading had done a good deal to prepare the way, and, later, when I became somewhat of a specialist and immersed myself in the studies known as ethnological, I was now and then startled by facts that would not square with orthodox scientific opinion, and by discoveries that seemed to hint at something still hidden for all our research. More particularly I became convinced that much of the folk-lore of the world is but an exaggerated account of events that really happened, and I was especially drawn to consider the stories of the fairies, the good folk of the Celtic races. Here I thought I could detect the fringe of embroidery and exaggeration, the fantastic guise, the little people dressed in green and gold sporting in the flowers, and I thought I saw a distinct analogy between the name given to this race (supposed to be imaginary) and the description of their appearance and manners. Just as our remote ancestors called the dreaded beings "fair" and "good" precisely because they dreaded them, so they had dressed them up in charming forms, knowing the truth to be the very reverse. Literature, too, had gone early to work, and had lent a powerful hand in the transformation, so that the playful elves of Shakespeare are already far removed from the true original, and the real horror is disguised in a form of prankish mischief. But in the older tales, the stories that used to make men cross themselves as they sat round the burning logs, we tread a different stage; I saw a widely opposed spirit in certain histories of children and of men and women who vanished strangely from the earth. They would be seen by a peasant in the fields walking towards some green and rounded hillock, and seen no more on earth; and there are stories of mothers who have left a child quietly sleeping with the cottage door rudely barred with a piece of wood, and have returned, not to find the plump and rosy little Saxon, but a thin and wizened creature, with sallow skin and black piercing eyes, the child of another race. Then, again, there were myths darker still; the dread of witch and wizard, the lurid evil of the Sabbath, and the hint of demons who mingled with the daughters of men. And just as we have turned the terrible "fair folk" into a company of benignant, if freakish, elves, so we have hidden from us the black foulness of the witch and her companions under a popular _diablerie_ of old women and broomsticks and a comic cat with tail on end. So the Greeks called the hideous furies benevolent ladies, and thus the northern nations have followed their example. I pursued my investigations, stealing odd hours from other and more imperative labors, and I asked myself the question: Supposing these traditions to be true, who were the demons who are