The phenomena known under the general name of spirit-manifestations vary greatly in different instances. In some cases they take the form of strange dreams, in which some warning or information concerning coming events is given that afterward proves true. In others they occur as seeming apparitions of persons recently or long dead. In others, as in the case of haunted houses, there are noises of great variety, moving of objects, opening and shutting of doors, appearances of unknown forms, and all the phenomena which might be produced by an invisible inhabitant of the house who was able to become visible under certain circumstances. More ordinary manifestations are rapping sounds and lifting of heavy bodies, writing either with or without apparent human agency, and mental communication of facts unknown to or forgotten by the persons present. Other phases are those presented by professional mediums,--the tying and untying of ropes, playing on musical instruments, the production of luminous phenomena, slate-writing under tables, and the like. Performances of this character are usually done in the dark, and the fraud which may be present is therefore not easily detected. It is impossible to apply tests under such circumstances, and nothing can be accepted as positive that cannot be tested. Performances similarly surprising are constantly offered by professional conjurers, and nothing claiming the high origin of spiritual phenomena can be received in evidence where trickery is possible or has not been rendered impossible by the employment of adequate tests. To the same class belong the cabinet performances and the so-called materialization of spirit forms, which have been the favorite cards of professional mediums of late years. So far as yet offered in public, they may be dismissed in the mass as pure trickery. The fact that stage-performers of sleight-of-hand tricks can repeat the cabinet phenomena in every detail, and that the materialized spirit showmen have been caught in numerous instances in the very act of fraud, throws utter discredit on the business. No repetition by new mediums of other forms of the exposed tricks carries any weight. In fact, in a matter of such importance nothing can be accepted as settled until it has been subjected to the strictest scientific tests and every possible opportunity for deceit or trickery eliminated. We are not ready to believe that the spirits of our departed friends are able and willing to talk with or show themselves to us, or create disturbances in the arrangement of our furniture, unless we are absolutely positive that our eyes, ears, and nerves are not being cleverly fooled by some skilled and unscrupulous show-man, or that we are not self-deceived by some temporary vagary of our brains or senses.