The taking of spirit photographs under so-called “test conditions” has frequently been carefully investigated by men of high reputation in other walks of life, chiefly men of letters and men of science. In many cases they have been unable to detect any trickery, and after due consideration have decided that they know of no natural means by which the results obtained could be produced, under the conditions employed. This is in itself a perfectly fair conclusion; but it does not follow that because they know of no natural method, no such method can exist; unfortunately the argument is frequently carried to this stage. Let us suppose that an eminent physicist watches a sleight-of-hand conjuror, who produces a dozen or more eggs from a small velvet bag, which was unquestionably empty when examined by the audience a few seconds previously; he will certainly not assume mediumistic powers on the part of the conjuror, or postulate the materialisation of a spirit hen. He realises that he is being deceived; he has had no training in conjuring, and does not know what to look for in order to “see through” the trick. How, then, does he expect to be able to detect a trick played upon him, probably in the dim light of a photographic dark-room, by a clever medium who has every method of trickery at his fingers’ ends? Even if he knew what to look for, the chances would be all in favour of the medium under the conditions which usually obtain; and in actual fact he probably has no idea of the multiplicity of methods which may be used for his deception. It seems therefore desirable to enumerate some of the many methods by which spurious spirit photographs may be produced. The following list makes no pretensions to being complete, but may give some idea of the variety of methods which the accomplished spirit photographer has at his service. _Group I._--_Methods Involving Double Exposure and Substitution_, in which a plate previously prepared with an undeveloped extra is substituted for the plate provided by the sitter. This gives excellent photographs, as the extra may be as distinct in detail as is desired, and the exposures can be calculated to a nicety, giving a suitably transparent spirit with a more solid portrait of the sitter. The substitution of the plate may be effected at almost any stage in the proceedings, for example: (_a_).--Methods involving substitution of the entire packet: 1. The medium may be in league with the shop from which the plates are purchased, the unfortunate sitter buying a box of plates already prepared with spirits. Wise sitters buy their plates at a distance, but mediums frequently demand a particular brand of plate, and if those brought by the sitter are declared unsuitable, he will have to go out and purchase the correct ones. He is naturally supplied with the address of the nearest photographic dealer, and the name of the brand of plates is written on a slip of paper to show the shopman; this ensures no mistake being made.