The question of the intervention of spirits might be decided from the tenor or content of the revelations, in any case in which this content would be such as evidently could not have originated in the human mind. It is not my intention to discuss this point. The present study takes cognizance solely of movements of inert bodies, and we have only to consider, among the arguments of M. de Gasparin, those which are included in this field of view.
Now, his arguments on this point seem to me to be all summed up in these slightly ironical lines: "Strange spirits! ... whose presence or absence could depend upon a rotation, depend upon cold or warmth, or health or disease, on high spirits or lassitude, on an unskilful company of unconscious magicians! I have the headache or the grip, therefore the daemonic beings will not be able to appear to-day."
M. de Mirville, who believes in spirits who manifest themselves through the agency of the fluid, might reply to Gasparin that the conditions of the ostensible manifestation of spirits are perhaps the fluidic state itself; that if this is so, we might very well, in a séance phenomenon, have a fluidic manifestation without the intervention of spirits, but not the intervention of spirits without a preliminary fluidic manifestation, and that, thus, anyone will invite such manifestation only at his own risk and peril.
Thury next discusses how the question of spirits ought to be considered.
The task of science (he writes) is to bear witness to the truth. It cannot do so if it borrows a part of its data from revelation or from tradition; to do this would be a begging of the question, and the testimony of science would become worthless.
The facts of the natural order are connected with two categories of forces, the one that of necessity, the other that of freedom. To the first belong the general forces of gravitation, heat, light, electricity, and the vegetative force. It is possible that we may discover others some day; but at present they are the only ones we know. To the second category belong solely the mind of animals and that of man. These are truly forces, since they are the cause of movements and of various phenomena in the physical world.
Experience instructs us that these mental forces manifest themselves by the intermediary of special organisms, very complex in the case of man and the superior animals, but simple in that of the lowest, among which latter class mind has no need of muscles and nerves in order to manifest itself externally, but seems to act directly upon a homogeneous matter, the movements of which it determines (the amœba of Ehrenberg). It is in these elementary organizations that the problem of the action of mind on matter is stated, after a fashion, in its simplest terms.
When once we have admitted the existence of the will as distinct, at least in principle, from the material body, it becomes solely a question of experience to ascertain whether other wills than that of man and the animals play any rôle whatever, frequent or occasional, on the stage of life. If these wills exist, they will have some means or other of manifestation, with which experience alone can make us acquainted. As a matter of fact, all that it is possible to affirm, a priori, is that, in order to appear, they must manifest themselves through some one of the forms of the eternal substance we call matter. But, to say that this matter must necessarily have an organization of muscles, nerves, etc., would be to hold to a very narrow idea, and one already belied by observation of the animal kingdom in its lower types. As long as we do not know what the bond is that unites the mind to the matter in which it manifests itself, it would be perfectly illogical to lay down, a priori, particular conditions which matter must observe in this manifestation. These conditions are at present wholly undetermined. Thus we are at liberty to seek for signs of these manifestations in the cosmic ether or in ponderable matter; in the gases, the liquids, or the solids; in unorganized matter, or particularly in matter already organized, such as that of which man and the animals are built up. It would be poor logic to affirm that other wills than those of men and animals cannot be discovered, on the ground that, heretofore, nothing of the kind has been seen; for facts of this kind may have been observed, but not scientifically elucidated and authenticated. Furthermore these wills might appear only at long intervals, or what seem long to us; but the vast abysses of nature's epochs are not to be spanned by our little memories or measured by the momentary duration of our lives.
Such are the facts and the ideas set forth in this conscientious monograph of Professor Thury. It is easily seen that, in his opinion (1) the phenomena are positive facts; (2) that they are produced by an unknown substance, to which he gives the name psychode, a something that, by the hypothesis, exists in us and serves as the intermediary between the mind and the body, between the will and the organs, and can project itself beyond the limits of the body; (3) that the hypothesis of spirits is not absurd, and that there may exist in this world other wills than those of man and the animals, wills capable of acting on matter.
Professor Marc Thury died in 1905, having devoted his entire life to the study of the exact sciences. His specialty was astronomy.