Cannot two brains that vibrate in unison at a distance of many kilometres be moved by the same psychic force? Cannot the emotion which starts from a brain reach a brain vibrating at no matter what distance, just as sound crosses a room, making the strings of a piano or violin vibrate? Do not forget that our brains are composed of molecules which do not touch, and which are in constant vibration. And why speak of brains? Cannot thought, will, psychic force, whatever its nature may be, act on a being to whom it is attached by the sympathetic and indissoluble ties of intellectual relationship? Do not the palpitations of a heart suddenly transmit themselves to the heart which beats in unison with ours? Are we to admit in the cases of apparitions noted above that the mind of the dead has really assumed a corporeal form when near the observer? In the greater part of the cases this hypothesis does not seem necessary. In our dreams we think we see persons who are not before our closed eyes at all. We see them perfectly, as well as in broad daylight; we speak to them, converse with them. Surely it is neither our retina nor our optic nerve which sees them, any more than our ear hears them. Our cerebral cells alone are concerned in it. Certain apparitions may be objective, exterior, and substantial; others may be subjective,--in that case the being who manifests himself would act from a distance on the being who sees, and this influence on his brain would determine the interior vision which appears exterior, as in dreams, but may be purely subjective and interior. Just as a thought, a memory, may arouse an image in our minds which may be very distinct and very vivid, just so one intelligence acting upon another may make an image appear in him which will for a moment give him the illusion of reality. It is not the retina which is affected by a positive reality, it is the optic thalami of the brain which are excited. In what way? The present state of our physiological and psychological knowledge does not yet teach us that. Such are the most rational inductions which it seems possible to derive from the phenomena to which we have just been giving our attention,--unexplained, but very old phenomena; for the histories of all peoples, from the highest antiquity, have preserved examples of it which it would be very difficult to deny or efface. But it will be asked, ought we, can we, admit in our age of experimental methods and positive science that a dying or even a dead man can communicate with any one? What is a dead man?