“It is doubtless a peculiar psychical state that confers mediumistic power, but we know nothing of its nature, and we often ruin our experiments and lose our results by our ignorance. Certainly it is very probable that the psychical state of those present at a seance will be found to re-act on the medium. We should get no results if our photographic plates were exposed to the light of the room simultaneously with the luminous image formed by the lens. In every physical process we have to guard against disturbing causes.
If, for example, the late Prof. S.P. Langley, of Washington, in the delicate experiments he conducted for so many years – exploring the ultra red raditation of the sun – had allowed the thermal radiation of himself or his assistants to fall on his sensitive thermoscope, his results would have been confused and unintelligible. We know that similar confused results are obtained in psychical research, especially by those who fancy the sole function of a scientific investigator is to play the part of an amateur detective; and accordingly what they detect is merely their own incompetency to deal with problems the very elements of which they do not understand and seem incapable of learning. Investigators who, taking an exalted view of their own sagacity, enter upon this inquiry with their minds made up as to the possible or impossible, are sure to fail. Such people showuld be shunned, as their habit of thought and mode of action are inappropriate, and therefore essentially vulgar, for the essence of vulgarity is inappropriateness.
Inasmuch as we know nothing of the peculiar psychical state that constitutes mediummship, we ought to collect and record all conditions which attend a scucessful seance. Mediumship seems in some points analogous to ‘rapport’ in mesmeric trance, and it would be interesting to know whether a mesmeric sensitive is more open to mediumship than the rest of mankind. Again, are those who are good percipients in telepathic experiments also percipients in spontaneous telepathy, such as apparitions at the moment of death, and are these again hypnotic sensitives? Similar questions also arise as to somnambulists; in a word, is there anything in common between the obscure psychical states of these different classes of sensitives? Very probably there is, for all psychical phenomena, as we shall see directly, involve to a greater or less extent the operation of an unconscious part of our personality, a hidden self which in a medium emerges from its obscurity, as the normal consciousness and self-control subsides. This fact does, indeed, afford some clue to the peculiar psychological condition of mediumship.”
– from p. 120-122 of On the Threshold of the Unseen, by Sir William Barrett, F.R.S. (1917)
In researching parapsychology it has been fascinating to see how these studies have developed over 130 years of scientific scrutiny since the official founding of the Society for Psychical Research in 1882. Existing in a liminal realm of inquiry which penetrates both the center and the periphery of human experience, studying the history of investigation into exceptional human experiences provides a very potent ground for understanding the intellectual development of the past century.