It is impossible to arrange these groups in one continuous logical series. But, roughly speaking, the degree in which the psychical collision is _recollected_ on either side may in some degree indicate its _intensity_, and may serve as a guide to our provisional arrangement. Following this scheme I shall begin with a group of cases which seem to promise but little information,--cases, namely, where A, the agent, in some way impresses or invades P, the percipient,--but nevertheless neither A nor P retains in supraliminal memory any knowledge of what has occurred. Now to begin with we shall have no difficulty in admitting that cases of this type are likely often to occur. The psychical _rapprochement_ of telepathy takes place, _ex hypothesi_, in a region which is subliminal for both agent and percipient, and from whence but few and scattered impressions rise for either of them above the conscious threshold. Telepathy will thus probably operate far more continuously than our scattered glimpses would in themselves suggest. But how can we outside inquirers know anything of telepathic incidents which the principals themselves fail altogether to remember? In ordinary life we may sometimes learn from bystanders incidents which we cannot learn from the principals themselves. Can there be bystanders who look on at a psychical invasion? The question is of much theoretical import. On my view that there is a real transference of something from the agent, involving an alteration of some kind in a particular part of space, there might theoretically be some bystander who might discern that alteration in space more clearly than the person for whose benefit, so to say, the alteration was made. If, on the other hand, what has happened is merely a transference of some impulse "from mind to mind";--then one can hardly understand how any mind except the mind aimed at could perceive the telepathic impression. Yet, in _collective_ cases, persons in whom the agent feels no interest, nay, of whose presence along with the intended percipient he is not aware, do in fact receive the impression in just the same way as that intended percipient himself. This was explained by Gurney as probably due to a fresh telepathic transmission,--this time from the due or original percipient's mind to the minds of his neighbours of the moment. Such a supposition, however, in itself a difficult one, becomes much more difficult when the telepathic impulse has never, so far as we know, penetrated into the due or intended percipient's mind at all. If in such a case a bystander perceives the invading figure, I must think that he perceives it merely as a bystander,--not as a person telepathically influenced by the intended percipient, who does not in fact perceive anything whatsoever. I quote in illustration a bizarre but well-attested case (see Appendix VI. C) which this explanation seems to fit better than any other.