Our study of Mr. Kirk’s little tractate must have a double aspect. It must be an essay partly on folk-lore, on popular beliefs, their relation to similar beliefs in other parts of the world, and the residuum of fact, preserved by tradition, which they may contain. On the other hand, as mental phenomena are in question—such things as premonitions, hallucinations, abnormal or unusual experiences generally—a criticism of Mr. Kirk must verge on “Psychical Research.” The Society organised for that difficult subject certainly takes a vast deal of trouble about all manner of odd reports and strange visions. It “transfers” thoughts of no value, at a great expense of time and of serious hard work. But, as far as the writer has read the Society’s Proceedings, it “takes no keep,” as Malory says, of these affairs in their historical aspect. Whatever hallucination, or illusion, or imposture, or the “subliminal self” can do to-day, has always been done among peoples in every degree of civilisation. An historical study of the topic, as contained in trials for witchcraft, in the reports of travellers and missionaries, in the works of the seventeenth-century Platonists, More, Glanvill, Sinclair, and others, and in the rare tracts such as _The Devil in Glen Luce_ and _The Just Devil of Woodstock_, not to mention Lavater, Wierus, Thyræus, Reginald Scott, and so on, is as necessary to the psychologist as to the folk-lorist.[1] If there be an element of fact in modern hypnotic experiments (a matter on which I have really no opinion), it is plain that old magic and witchcraft are not mere illusions, or not commonplace illusions. The subliminal self has his stroke in these affairs. Assuredly the Psychologists should have an historical department. The evidence which they would find is, of course, vitiated in many obvious ways, but the evidence contains much that coincides with that of modern times, and the coincidence can hardly be designed—that is to say, the old Highland seers had no design of abetting modern inquiry. It may be, however, that their methods and ideas have been traditionally handed down to modern “sensitives” and “mediums.” At all events, here is an historical chapter, if it be but a chapter in “The History of Human Error.” These wide and multifarious topics can only be touched on lightly in this essay; the author will be content if he directs the attention of students with more leisure and a better library of _diablerie_ to the matter. But first we glance at _The Secret Commonwealth_ as folk-lorists. III. “THE SUBTERRANEAN INHABITANTS.”