Trowbridge and Burbank — Source of the X-rays. 133 



X-rays. When the tube represented in fig. 9 had reached a 

 certain stage of exhaustion, a bit of tin-foil connected to a zinc 

 plate 10xl6 cni and l mm thick, was stuck upon the outside of 

 the tube where the mirror formed the fluorescent spot. This 

 zinc plate was carefully insulated from the ground. It was 

 seen that a bundle of rays was reflected by the tin-foil to the 

 opposite wall of the tube, showing a well-defined shadow of 

 the mirror and the continuous conductor on this wall. The 

 direction of this shadow could be changed at will by changing 

 the position of the tin-foil. This phenomenon was produced 

 both when the wire was the cathode and when it was the 

 anode. It can be explained on the hypothesis that a layer of 

 electrified particles is held by a condenser action on the wall 

 of the tube and that the fresh coming particles are strongly 

 repelled by those that have accumulated at the spot. 



The behavior of aluminum toward the X-rays is so remark- 

 able that it merits especial investigation. Can it be that it 

 manifests a remarkable condenser action toward the high elec- 

 tromotive forces which produce the X-rays, similar to the 

 action which has been observed at lower voltages ?* We con- 

 nected to the air pump, at the same time, two exactly similar 

 tubes, one of which had two pointed terminals of platinum, 

 the other two pointed terminals also; but one consisted of 

 aluminum and the other of platinum. The discharge from a 

 Ruhmkorf coil was sent through these tubes which were in 

 multiple circuit. At a certain stage of the exhaustion it was 

 seen that the discharge passed more easily when the aluminum 

 wire was made a cathode than when it constituted the anode. 

 When the wire terminals in both tubes were made of thin 

 discs, the difference was less marked. This might have been 

 surmised, from previous investigations on the effect of form 

 of electrodes on resulting polarization. f It may be that the 

 anomalous action of aluminum in respect to X-rays is due to 

 a species of dielectric polarization on the surface of the plati- 

 num and that thus the surface becomes a new source of elec- 

 trostatic stress, similar to that which was observed by connect- 

 ing a bit of tin-foil and a capacity to the tube. Since we are 

 dealing with very high differences of potential and with high 

 charges on the ions, the instantaneous exhibition of electrical 

 energy is very great and might probably explain the diffusion 

 of this energy through the air. According to this hypothesis 

 the light manifestations of the X-rays arise only at the fluor- 

 escent screens, or at other suitable surfaces. 



*L. Graetz, Wied. Ann., No. 10, 1897, p. 323. 



f Karl Robert Klein, Wied. Ann., No. 10, 1897, p. 259. 



