TROWBRIDGE. — ELECTRICAL DISCHARGES. 447 



"With the employment of a jjowerful Ruhmkorf coil giving sparks of at 

 least eight inches, X-rays could be detected in this tube, and when the 

 tube was connected with the Plante machine, the X-rays gave strong 

 effects in the fluoroscope. 



In order to test the question whether the so called cathode rays and 

 X-rays are generated primarily only at the cathode, a very large resist- 

 ance of distilled water was interposed in the circuit with the continuous 

 wire tube (Fig. 9) in order to damp any oscillations which miglit arise. 

 The circuit thus consisted of the tube, the water resistance, a spark gap, 

 and the secondary coil of a large Ruhmkorf. The tube was connected at 

 first permanently to the air pump. As the exhaustion proceeded a beam 

 of rays proceeded from the mirror on the contiimous conductor which was 

 focused on the wall of the tube. This beam was more brilliant and pro- 

 duced a stronger fluorescence on the tube when the wire was uesjative 

 than when it was positive. At a higher stage of the vacuum, however, 

 very little if any difference could be detected in the appearance of the 

 tube, and X-rays could be detected outside the tube opposite the fluores- 

 cent spot caused by the mirror. That is, the X-rays were given off 

 when the wire constituted both the cathode of the circuit and also the 

 anode. It seems, therefore, that the term cathode rays is not a general 

 one. It would seem that electric rays might be a more comprehensive 

 one for both cathode rays and X-rays. 



Furthermore the phenomenon of electrostatic induction plays an im- 

 portant part in the phenomena of the so called X-rays. When the tube 

 represented in Figure 9 had reached a certain stage of exhaustion, a bit 

 of tin-foil connected to a zinc plate 10 by 16 cm. and 1cm. 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 tliat 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 phenome- 

 non was pi'oduced both when the wire was the cathode and when it was 

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

 fied 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 aluminium toward the X-rays is so remarkable ihat 

 it merits especial investigation. Can it be that it manifests a remarka- 

 ble condenser action toward the high electromotive forces which produce 



