4. The medium may palm a positive transparency; if he is allowed to handle the plate he will hold it close to the red lamp with the transparency between; if the lamp is rather bright, or is not a very deep red, an impression is soon made on the plate.
5. With a pinhole in the dark-room lamp, and a transparency inside--a perfectly practicable arrangement with some of the more complicated dark-room “safe-lights,”--a pinhole projector can be formed, which will throw an image on a suitably-placed plate. Any leakage of white light into the dark-room, either from the lamp or from outside, can be used to produce blotches and streaks on the plate. A very little mechanical ingenuity will enable a medium who takes a pride in his work to rig up an arrangement of this kind which can be switched off and on at will and which will project an image on a predetermined spot on the bench. By the simple expedient of having the bench so cluttered up with bottles and miscellaneous rubbish that this spot is the only unencumbered one, the unsuspecting sitter may be forced to lay a plate on this spot while, for example, he is marking another. The medium may ostentatiously stand at the other end of the room and “switch on” for a moment while the sitter’s attention is engaged with his marking.
6. Photographic plates are sensitive to rays invisible to the eye, as has been pointed out in considering the effect of fluorescent substances. X-rays and ultra-violet rays, for instance, both invisible yet strongly actinic, might be used in the most baffling manner in the production of spirit extras. The expense and technical difficulties would be considerable, but were any medium to take the method up, he might safely defy the most critical investigation and would soon recoup himself for the few pounds initial outlay.
There are undoubtedly many other methods used by mediums for this purpose; but if the sitter who has obtained spirit extras under test conditions carefully considers the procedure employed, in the light of the suggestions made above, he will probably find that several loopholes were left by which fraud might have been introduced.
The argument most frequently brought forward, in favour of the genuineness of spirit photographs, is that the conditions employed in their taking leave no loophole for fraud. It has been pointed out in the preceding section that the usual “test conditions” leave not one, but many, such loopholes. Evidence of fraud has at some time or other been brought against most spirit photograph mediums, and they have consequently been more or less discredited. Other mediums have been more clever--or more fortunate--and many people therefore argue that they are not all to be tarred with the same brush; it is pointed out that spirit extras _have_ been obtained under the strictest conditions imposed by acute observers who have found nothing suspicious of trickery.
