This _spiritus mundi_, or "nervous principle," to which he supposes the ancients referred when they spoke of "the demon," is, according to his theory, the medium, or menstruum, by which, under certain conditions of "excitement," the thoughts and potencies of one mind, with its affections, emotions, volitions, etc., flow into another, giving rise to reflex expressions, which, to persons ignorant of this principle, have seemed possible only as the utterances of outside and supermundane intelligences. And as this same _spiritus mundi_, or demon, pervades and connects the mind equally with all _physical_ bodies, in certain _other_ states of "excitement" it moves those physical bodies, or makes sounds upon them, expressing intelligence--that intelligence always being a reflex of the mind of the person who, consciously or unconsciously, served as the exciting agent. Whatever elements of truth this theory, in a _different_ mode of application, might be found to possess, in the form in which it is here presented it is encumbered by two or three difficulties which altogether seem fatal. In the first place, it wears upon its face the appearance of a thing "fixed up" to meet an emergency, and which would never have been thought of except by a mind pressed almost to a state of desperation by the want of a theory to account for a class of facts. Look at it: "The spirit of the world identical with the nervous principle"!--the same, "when unduly _excited_," the medium by which a mind may _unconsciously_ move other minds and organisms, or even dead matter, in the expression of its own thoughts! Where is the shadow of proof? Is it anything more than the sheerest assumption? Then again: even if this mere assumption were admitted for truth, it would not account for that large class of facts referred to in the course of our remarks on the "Electrical theory," unless this _spiritus mundi_, demon, nervous principle, or spiritual medium, is made at once not only the "medium," but the intelligent and designing _source_ of the communication; for, as we have said before, it would be perfectly useless to deny that thoughts are sometimes communicated through the Planchette and similar channels, which positively never had any existence in the minds of any of the persons visibly present.