aluminum, and within the flesh." These experiments have since been repeated by many other investigators with perfect success; the observer in one case examining the bones of his own hand.
Gustave le Bon, in the Revue Scientifique, in summing up the results of his experiments on the X rays, says: "These experiments, which have been varied in all ways, are fundamental. They show us that the degree of thickness of the opaque plates is absolutely without importance in the passage of the 'lumière noire.' They also indicate that the 'lumière noire' is propagated under other laws than those which govern ordinary light. . . . This light can be transformed into radiations which propagate themselves as electric currents. They are not, however, electric radiations, because they produce effects which ordinary electric currents will not produce. We find ourselves, then, in the presence of a form of energy which is not light, as it only has part of light's properties and does not obey the laws of the propagation of light, and which is not electricity, since electricity in all known forms does not produce the same effects. The 'lumière noire' must be considered as a new force added to the few of these which we already know."
In a letter to Nature, Lord Blytheswood describes the following experiment with a Wimshurst electrical machine of one hundred and twenty-eight three-foot plates, the machine being driven by a motor of about one horse power and a half. "A thick sheet of lead was placed upright between the poles of the electric machine, as a screen, and was connected to the ground, the two poles being insulated. A sensitive dry plate was put into the camera dark slide, with a metallic object to be photographed (a steel washer with holes in it), and this was connected by a wire which passed out of the dark slide to the ground. The whole was wrapped up in four folds of a black velvet focusing cloth, and was put in some cases between the negative pole and the lead screen, and in other cases between the positive pole and the lead screen, the plane of the slide being perpendicular to the line of discharge. In all cases good strong negatives were obtained with exposures of about twenty minutes. The machine was arranged to give a silent brush discharge during the experiments." Several other physicists have reported obtaining shadow pictures without the aid of a Crookes tube, by using an electric current or simple sunlight, and a fluorescent screen, after very long exposures. Henri Becquerel recounts the following interesting experiment: "I inclose a photographic plate in two folds of very thick paper, so that the plate does not become shaded on exposure to the sun for a day. On the outside of this paper a plate of phosphorescent material is placed, and the whole is exposed to the direct rays of the sun for several hours. When the plate is developed we find