Looking at the question here solely from the general physical point of view, I do not follow M. de Gasparin (says Thury) in his exploitation of theological explanations. As to the second, I will only call attention to the suggestion that the sufficiency of explanations purely physical should strictly apply only to the Valleyres experiments, where, in truth, nothing gives evidence of the intervention of wills other than the human will. 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 seance 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.