from being credulous, were rather specialists in incredulity. A great deal of the work of the Societies consisted in, and still consists in, unmasking fraud or tracking down self-deception. Some of their members even learned professional "conjuring" in order to find out if certain alleged mediumistic phenomena, such as slate-writing, could not be duplicated by normal means. This negative part of their work2 has been so effective that the positive contributions are perhaps not equally well known.
Yet precisely because these researchers had studied fraud and self-deception, they have been able to work out methods that seem to prove the existence of telepathy and kindred "psychic" abilities, and to prove it by strictly scientific experimentalism.
No one can or should be convinced by mere assertions of this kind, but neither should anyone air his opinion on the matter without having studied the large technical literature now existing.3
Of the facts that seem to have been established by this kind of research, two are especially relevant to an understanding of Swedenborg—telepathy, or, more broadly speaking "extrasensory perception," and precognition, defined as "a noninferential knowledge of the future."
So far the studies made of Swedenborg (aside from those made by members of the sect started in England after his death) appear to take it for granted that the stories of his telepathy and precognition are either false reports or else signs of his supposed madness. Things would look different if any one of them could have been true. There is no doubt that Swedenborg began very early to puzzle over such phenomena. In 1733 or 1734 he was interested in precognitive dreams, and, as previously mentioned, he later made a list of passages he found in the classics concerning prophetic dreams. In his dream diary of 1744 he says, without giving details, that in a dream he had warning of two mortal dangers which enabled him to escape them. In another dream he says he saw the Moravian church in London and the curious way in which the congregation was dressed three months before he actually saw them. His very casualness in noting this makes one fancy he must have had similar dreams before.
Precognition seems to have played a part only in the early period of his supernormal experiences; after that they consisted mainly
