But these observations must, I suppose, have occurred to all who have considered such matters at all impartially, and however relevant they may be they will never by themselves prevail against what we call “the evidence of our senses.” No amount of general considerations of this kind will deter the credulous from accepting the _prima facie_ indications of a “successful” _séance_. The only hope of preserving the public from the depredations of these swindlers is to show that the “evidence of the senses” is not worth twopence unless backed by special knowledge of the relevant technique.
One would think that anyone who reads Mr. Patrick’s admirable account of fraudulent methods and of his experiments in their application will feel chary of claiming that he has wholly eliminated the possibility of fraud from any photographic _séance_ which he has attended. But there may be some who will still say: “No doubt these fraudulent methods can be and have been employed, no doubt many people would allow a medium to substitute plates under their very noses, or to touch them. But when _I_ went to such-and-such a medium I am _certain_ that the plates were never out of my possession, that he never had a chance of touching them....” and so forth.
Of course, some of the methods described by Mr. Patrick do not involve touching the plates at all. It would not be at all impossible for an artist in such work to allow a sitter to use his own plates, camera, slides, dishes, and chemicals in his own studio and dark-room, to load, unload, and develop the plates himself without their ever being touched by the “medium” and yet to produce a perfectly good extra.
But I will let that pass and confine myself to the question of whether the kind of positive statement outlined above is really worth anything at all. This question was answered once and for all in the emphatic negative by the classical experiments of the late Mr. S. J. Davey in “Slate-writing,” which are fully described in the _Proceedings of the Society for Psychical Research_, vols. iv. and viii.
These experiments are not nearly so widely known as they deserve to be, but it is not too much to say that no one who has not read, marked, learned, and inwardly digested them is competent so much as to begin to talk about the genuineness of spirit photography; unless, of course, he happens to have acquired a knowledge of trick methods and the scope of deception by other means--such as Mr. Patrick adopted in his experimental work!