Various explanations of the power employed by the spirits, assisted by the medium and by the circle, have been offered by the scientific investigators of the subject. The most generally accepted theory of the western scientists is that the spirits employ what is called the "psychic force" of the medium, often assisted by that drawn from the circle and focused in the medium. The medium is regarded as a psychic storage battery which is freely drawn upon by the manifesting spirit. The degree and character of the manifestations are determined largely by the peculiar quality of the psychic force, the capabilities of the medium, the knowledge and powers of the spirits, and the influence of the sitters.
Human Magnetism.
Dr. Dean Clarke says: "Human magnetism, or nerve aura, is probably the most sublimated form of ethereal matter, hence nearest in refinement to spirit substance, and therefore spirits use it as the vehicle of their vibrating forces. Those persons who have an excess of magnetism, of the proper quality to unite with both the psychic force of spirits and the forces inherent in natural objects, and thus form an electro-magnetic connection of spirits with the objects they wish to act upon, are the persons chosen by the spirits for physical mediums. The mind and brain of the medium are not often nor necessarily controlled, and only his magnetism and psychic forces are used, through which the spirits transmit the vibrations of their own power to mechanically produce concussions, or movements of material objects."
"Zoether."
Hudson Tuttle (writing under control) gives the following statement of a spirit concerning the manner in which physical phenomena are produced: "Zoether (psychic force) emanating from the medium charges the object to be moved, and a band of spirits directs a current of their own zoethic emanation in the direction they desire the article to move, and it passes along the current thus produced. The charging of the object by the medium is necessary in order that it may be in a state of vibration harmonious to the spirit current. If this current be directed against the table or other charged body, raps or concussions are produced, as a positive and negative relation exists between the spirits and the medium's zoether. One spirit alone cannot produce physical manifestations. If one purports to communicate, assistance will be rendered by many others, who combine their influence."
"Prana."
The orientals account for physical mediumistic phenomena in a similar way, though their terms are different. Instead of speaking of zoether, or psychic force, they always employ the term "prana." In the oriental philosophies "prana" is explained as a subtle form of energy permeating the universe, but manifesting in a special form in the organism of the human being. This subtle force, or prana, is held to be capable of being transmitted from one organism to another, and is held to be the energizing power by means of which many forms of occult or magic phenomena are produced. Prana is very much akin to the "human magnetism" of the western occultists, and the properties attributed to the latter are really those which the orientals for centuries past have held to be among the essential properties of prana; so, at the last, there is found to be a practical agreement here between the oriental and the western schools of occultism, respectively, in spite of their differing terminology.