630 B. The first experimental study of thought-transference was connected with the discovery that the somnambulistic state could be artificially induced, and the greater number of observations made during this early stage were carried out in this country during the second quarter of the nineteenth century. Thought-transference in these cases took the form of community of sensation between operator and subject, depending, as was supposed, on a specific rapport between them (see 571). The phenomenon was not studied by itself, but regarded as belonging essentially to mesmerism; consequently it shared in the discredit into which the latter fell, being only one of the numerous reported mesmeric marvels, which - speaking generally - were rejected wholesale and without inquiry.

The first impetus to the more recent scientific study of telepathy was given by Professor W. F. Barrett, F.R.S., who brought forward some results of his own with a hypnotised girl, in a paper read before the British Association in 1876. In the course of the correspondence arising out of his paper, Professor Barrett learnt of other instances, which he carefully investigated, in which telepathy had been observed in the normal waking state. Later, in the years 1881-2, a long series of experiments in which Professor Sidgwick, Professor Balfour Stewart, Edmund Gurney, myself, and others joined with Professor Barrett, seemed to establish the possibility of a new mode of communication from mind to mind. And these early results have been confirmed by further experiments continued down to the present time by observers both in this country and abroad.

At about the time of the early S.P.R. experiments in thought-transference, popular interest had been roused in the subject by the invention of the "willing game," and the discussions and experiments - especially of Professor Barrett and other members of the S.P.R. - which showed that success in the game depended on "muscle-reading," - that the subject was led to perform actions by unconscious guidance from the person touching him, in the same way that table-tilting, or even such complicated processes as writing, may be carried out by many persons in complete ignorance that their wills, or even their muscles, are concerned. Even if the subject is not in contact with any one, he may be guided through unconscious variations in tone of voice, gesture, or expression, by the persons watching his progress. On the other hand, if contact ceases before he begins to perform the required movement; or if, while in contact, he has only to say what mental impression he has received - as in experiments in guessing playing-cards, numbers, and the like - the possibility of unconscious guidance by contact is much reduced.

Since, however, it is impossible to make sure that guidance has not been operative under such circumstances, we cannot claim as evidence of thought-transference experiments in which contact has been allowed at any stage. The experiments cited here have been selected with a special view to the exclusion of these possible sources of error, and therefore no cases in which any contact had been allowed are given.

With regard to the possibility of deliberate collusion or fraud, no general statement can be made as to conditions that would absolutely exclude this. In the last resort, all scientific experiments rest on the bona fides of the experimenter. There are many psychological observations which cannot be controlled by others, or repeated at will, since they relate to subjective sensations, or depend on unknown conditions; but they are generally accepted as correct, because it is believed that the observers are genuinely interested in the truth of the facts. Similar presumption of the genuineness of experiments in thought-transference is afforded by the intelligence of the experimenters, the scientific standing of some of them, and the general spirit in which their work has been done, as may be seen from the detailed accounts, a few of which I now proceed to give.1