RECENT WORK ON THE X RAYS. 



107 



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 experi- 

 ments, 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 { lumiere 

 noire/ They also indicate that the ' lumiere 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 pres- 

 ence 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 'lumiere 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 sun- 

 light, and a fluorescent screen, after very long exposures. Henri 

 Becquerel recounts the following interesting experiment : " I in- 

 close 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 



