During the three years that I have experimented in psychology with Dr. Puel and his friends, there has been no _seance_ where we have not been able to determine more or less important phenomena of percussion. An experiment I love to make is that of striking my fingers on the table, either to imitate the music of a band with drum accompaniment with some known air, and the same sound is immediately produced on the under surface of the piece of furniture, with the same rhythm appearing to be invoked by an invisible hand performing under the table. This phenomenon is manifested sometimes spontaneously upon my demand or that of my assistant. I observed it one evening at my own house for more than a quarter of an hour from, the moment I entered the room; in this case the noise was a rolling, which appeared to arise from the metallic surface of a table. It was a member of my family who called my attention to the abnormal noise, so much the more curious, inasmuch as I could produce it at will, giving shades and variations expressed by the movements of my hand. In order to respond in advance to any objection, I will say it was two o’clock in the morning when this phenomenon was produced, and there was no passing carriages in the street to make any kind of a vibration. These phenomena of percussion are sometimes produced with a most extraordinary intensity, as in the observations of Kate Fox in the house at Hydesville; these were probably only phenomena of percussion similar to those observed at Louviers, in the home of Madame Gay, under the mediumship of Francoise Fontaine, in 1591, manifestations which were then attributed to the Devil, or later to a condition of hallucinations, among the witnesses, according to the _materialistic psychologists_ of the nineteenth century. CLASS III.—_Alteration of the weight of bodies._ The experiments made by Mr. Crookes, in regard to the alterations in the weight of bodies, enters the category of psychic phenomena examined with the most mathematical exactitude, by the aid of accurate registering apparatus. It is in these experiments that the celebrated English physician was able to witness _Psychic Force_ developed by his _medium_. The description and designs of the apparatus thus used may be found in the “_Moniteur de la Policlinique_,” of the 7th and 14th of May, 1882, and in “_Le Spiritisme_” of Dr. Paul Gibier, published in the year 1887. This article is too lengthy for reproduction in this work, but we have the right to consider it as the point of departure for experimental psychology, for not only have they not been denied in France and other countries, but _they have been recognized as absolutely true_, by several colleagues of Mr. Crookes, belonging to the _Royal Society of London_. CLASS IV.—_Movements of heavy bodies at a distance from the medium._