This case did not have for me the same _absolute certainty_ as the preceding. There are degrees in the feeling of security we have in observations. In astronomy, even, there are stars at the limit of visibility. And yet in the opinion of all the participators in the seance there was no trick. Besides, on another occasion, at my own home, I saw another figure, that of a young girl, as the reader will see in the third chapter. 8. That same day, at Montfort, in the course of the conversation, some one recalled the circumstance that the "spirits" have sometimes impressed on paraffin or putty or clay the print of their head or of their hands,--a thing that seems in the last degree absurd. But we bought some putty at a glazier's and fixed up in a wooden box a perfectly soft cake. At the end of the seance there was the imprint of a head, of a face, in this putty. In this case, no more than in the other, am I _absolutely certain_ there was no trickery. We will speak of it farther on. Other manifestations will be noted in subsequent pages of this book. Stopping right here, for the present, at the special point of view of the proved existence of unknown forces, I will confine myself to the six preceding cases, regarding them as incontestable, in the judgment of any man of good faith or of any observer. If I have considered these particular cases so early in the work, it is in response to readers of my works who have been begging me for a long time to give my _personal_ observations. The simplest of these manifestations--that of raps, for example--is not a negligible asset. There is no doubt that it is one or another of the experimenters, or their dynamic resultant, that raps in the table without knowing how. So, even if it should be a psychic entity unknown to the mediums, it evidently makes use of them, of their physiological properties. Such a fact is not without scientific interest. The denials of scepticism prove nothing, unless it be that the deniers themselves have not observed the phenomena. I have no other aim in this first chapter than to give a preliminary summary of the observed facts. I do not desire to put forth in these first pages any explanatory hypothesis. My readers will themselves form an opinion from the narratives that follow, and the last chapter of the volume will be devoted to theories. Yet I believe it will be useful to call attention at once to the fact that matter is not, in reality, what it appears to be to our vulgar senses,--to our sense of touch, to our vision,--but that it is identical with energy, and is only a manifestation of the movement of invisible and imponderable elements. The universe is a dynamism. Matter is only an appearance. It will be useful for the reader to bear this truth in mind, as it will help him to comprehend the studies we are about to make.