We have thus, according to the advice of Socrates, permitted the argument to lead us whither it would.  And whither has it led us?  The old, savage, natural theory of ghosts and wraiths is that they are spirits, yet not so immaterial but that they can fill space, be seen, heard, touched, and affect material objects.  Mediaeval and other theologians preferred to regard them as angelic or diabolic manifestations, made out of compressed air, or by aid of bodies of the dead, or begotten by the action of angel or devil on the substance of the brain.  Modern science looks on them as hallucinations, sometimes morbid, as in madness or delirium, or in a vicious condition of the organ of sense; sometimes abnormal, but not necessarily a proof of chronic disease of any description.  The psychical theory then explains a sifted remnant of apparitions; the coincidental, ‘veridical’ hallucinations of the sane, by telepathy.  There is a wide chasm, however, to be bridged over between that hypothesis, and its general acceptance, either by science, or by reflective yet unscientific inquirers.  The existence of thought-transference, especially among people wide awake, has to be demonstrated more unimpeachably, and then either the telepathic explanation must be shown to fit all the cases collected, or many interesting cases must be thrown overboard, or these must be referred to some other cause.  That cause will be something very like the old-fashioned ghosts.  Perhaps, the most remarkable collective hallucination in history is that vouched for by Patrick Walker, the Covenanter; in his Biographia Presbyteriana. {209} In 1686, says Walker, about two miles below Lanark, on the water of Clyde ’many people gathered together for several afternoons, where there were showers of bonnets, hats, guns, and swords, which covered the trees and ground, companies of men in arms marching in order, upon the waterside, companies meeting companies. . . . and then all falling to the ground and disappearing, and other companies immediately appearing in the same way’.  This occurred in June and July, in the afternoons.  Now the Westland Whigs were then, as usual, in a very excitable frame of mind, and filled with fears, inspired both by events, and by the prophecies of Peden and other saints.  Patrick Walker himself was a high-flying Covenanter, he was present:  ’I went there three afternoons together’—­and he saw nothing unusual occur.  About two-thirds of the crowd did see the phenomena he reckons, the others, like himself, saw nothing strange.  ‘There was a fright and trembling upon them that did see,’ and, at least in one case, the hallucination was contagious.  A gentleman standing next Walker exclaimed:  ’A pack of damned witches and warlocks, that have the second sight, the deil ha’t do I see’.  ’And immediately there was a discernable change in his countenance, with as much fear and trembling as any woman I saw there, who cried out:  “O all ye that do not see, say nothing; for I perswade