I have made a very careful personal investigation of the surviving Celtic Fairy-Faith by living for many months with and among the people who preserve it; I have compared fairy phenomena and the phenomena said to be caused by gods, genii, daemons, or spirits of different kinds and recorded in the writings of ancient, mediaeval, and modern metaphysical philosophers, Christian and pagan saints, mystics, and seers, and now more or less clearly substantiated by from thirty to forty years of experimentation in psychical sciences by eminent scientists of our own times, such as Sir William Crookes and Sir Oliver Lodge in England, and M. Camille Flammarion in France. As a result, I am convinced of the very great value of a serious study of the Fairy-Faith. The Fairy-Faith as the folk-religion of the Celts ought, like all religions, to be studied sympathetically as well as scientifically. To those who take a materialistic view of life, and consequently deny the existence of spirits or invisible intelligences such as fairies are said to be, we should say as my honoured American teacher in psychology, the late Dr. William James, of Harvard, used to say in his lectures at Stanford University, 'Materialism considered as a system of philosophy never tries to explain the _Why_ of things.' But in our study of the Fairy-Faith we shall attempt to deal with this _Why_ of things; and, then, perhaps the value of studying fairies and Fairyland will be more apparent, even to materialists. The great majority of men in cities are apt to pride themselves on their own exemption from 'superstition', and to smile pityingly at the poor countrymen and countrywomen who believe in fairies. But when they do so they forget that, with all their own admirable progress in material invention, with all the far-reaching data of their acquired science, with all the vast extent of their commercial and economic conquests, they themselves have ceased to be natural. Wherever under modern conditions great multitudes of men and women are herded together there is bound to be an unhealthy psychical atmosphere never found in the country--an atmosphere which inevitably tends to develop in the average man who is not psychically strong enough to resist it, lower at the expense of higher forces or qualities, and thus to inhibit any normal attempts of the Subliminal Self (a well-accredited psychological entity) to manifest itself in consciousness. In this connexion it is highly significant to note that, as far as can be determined, almost all professed materialists of the uncritical type, and even most of those who are thinking and philosophizing sceptics about the existence of a supersensuous realm or state of conscious being, are or have been city-dwellers--usually so by birth and breeding. And even where we find materialists of either type dwelling in the country, we generally find them so completely under the hypnotic sway of city influences and mould