7.--Materialisation-sittings with the assistance of professional mediums form a distinct category of phenomena. They cannot be classed under the head of “communications,” and they are just as much physical as psychical. Their chief defect is that they are not “open and above-board,” as is the case with the analogous proceedings of ordinary “table-turning” in private circles, where very astounding movements, etc., take place in full light. For some reason or another--good, bad or indifferent--but never on account of any real necessity, materialising mediums in the majority of cases insist upon the sittings taking place in darkness, and upon the use of “cabinets” and screens in the shelter of which the spirits are understood to make their preparations for the show they are about to give. The sitters, of course, cannot interfere: a patient does not instruct the physician with respect to what prescription is needful. Each medium must be allowed to go about his business in his own way; and each sitter is equally free to make his own observations and form his own conclusions. The stock phenomena in dark _séances_ are the sounding of musical instruments laid upon the table for the purpose and their being moved about through the air, the sitters occasionally feeling themselves touched by the articles in question. Then, too, fitful lights are seen here and there in the room, and voices are heard speaking or singing. Small objects, such as flowers, are tossed about, and larger ones, such as chairs, couches, etc., are moved--often with great violence. It is, moreover, not an uncommon occurrence for detached hands and faces, faintly luminised, to become visible; while, sometimes, what appear to be full-sized simulacra of human beings mix with the sitters. The medium in charge of such sitting is usually tied to a chair or held by some of the sitters in such as way as to prevent any trickery. This course of action should not, however, be pursued. Sitters do not attend _séances_ for the sake of amusement or for the purpose of witnessing a clever conjuring exhibition. There ought not to be any question of a contest of wits between the sitters and the medium. The real object to be striven for is the completeness of the manifestations; and this can best be attained by giving the medium and the spirits the freest of free play.