I am aware that many will ridicule the idea of such a simple trick being played upon an intelligent observer; but any conjuror, whose business it is to do this kind of thing, knows that it is remarkably easy.
5. Sometimes the first photographs taken are blanks, the sitter then returns to the dark-room and loads up some fresh plates out of the packet. It may not occur to him that an accomplice of the medium has had access to the dark-room in the meantime, and when he gives this account of the séance a few days later he will probably have entirely forgotten that the plates were not all loaded at once.
Substitution can, of course, be effected in many other ways; every medium probably has his favourite method which he chiefly practises.
It may be pointed out here that in the case of a regular sitter who always marks his plates in the same way, as most do, it would not be at all difficult to forge his signature on a prepared plate and substitute this for one of the marked plates.
Group II.—Other Methods, conveniently classified as follows:
(a).—Methods involving preparation of the studio:
1. An accomplice may be concealed behind the sitter, and be photographed with him; this is the simplest way of all, the sitter facing the camera, and, being told not to move during the exposure, is unaware that a “spirit face” is behind him, framed in an unsuspected opening in the background. Being behind the sitter, the face will be a little out of focus, and will appear rather blurred on the negative.[6]
2. It has been suggested that a mirror, or sheet of glass—on the principle of “Pepper’s Ghost”—may be introduced behind the sitter, producing the spirit by reflection of an accomplice hidden from the sitter. In practice this would be rather complicated and difficult to conceal; it would seem to have no advantage over the preceding method.
3. The extra is frequently sketched on the background—especially if this be a plain one—in some fluorescent substance, such as quinine sulphate. Such a sketch is invisible to the eye, but visible to the photographic plate. Many of Boursnell’s spirits appear to have been produced in this manner.
(b).—Methods involving the camera and dark slides: