128 On Alternating Discharges in vacuo. 



the approach of the fluorescent surface a' to V when contact 

 is made, and its return to its original position so soon as con- 

 tact is broken, can be easily observed. 



This attraction is very easily explained. When the points 

 a and b are touched, currents are excited, as we know, which 

 start from the corresponding points of the inner wall of the tube, 

 and propagate themselves in straight lines through the tube 

 in the directions a' to a and V to b (if we take account only of 

 the positive electricity); we obtain, therefore, in this case two 

 similarly directed and intersecting currents, which, as we know, 

 attract each other and bring about the approach of the fluo- 

 rescent surfaces. 



If we again touch the tube at a so that the fluorescent sur- 

 face appears at a', and if then the tube be also touched with 

 a conductor at a point close to a! ', we observe a repulsion of 

 the fluorescent surface. In this case also the motion is most 

 easily observed by maintaining contact with a, and alternately 

 making and breaking the other contact. In this case we have 

 the mutual action of oppositely directed currents wirich, we 

 know, repel each other. When contact is made with more 

 than two points of the tube, the relative position of the sur- 

 faces is altered. This alteration can, however, easily be ex- 

 plained by well-known electrodynamic action. 



I take this opportunity of pointing out the want of agree- 

 ment in the result of this experiment with that of Crookes's 

 experiment. Crookes passed two similarly directed currents 

 through a highly exhausted tube, having at the one end two 

 electrodes side by side, both connected with the negative pole, 

 and at the other end only one electrode, which was made the 

 positive pole. We obtain then two similar currents travers- 

 ing the vacuum. By the use of a properly adjusted screen 

 with two openings near the negative electrode, Crookes ob- 

 tained two well-marked currents, the paths of which were 

 observed by means of a fluorescent screen. Both currents 

 were found to deviate from their normal path in consequence 

 of repulsion. It would be of great interest to repeat this ex- 

 periment, and to investigate, by means of such a tube, the 

 different action on each other of the induced currents, and 

 especially their electrodynamic action ; but, unfortunately, I 

 have not yet been able to obtain such a tube. 



The properties and action of induced currents investigated 

 in this paper afford an explanation of the phenomenon first 

 observed by Beitlinger with certain tubes, viz. the so-called 

 repulsion of the direct current of the tube when the tube is 

 touched with a conductor, since the repulsion thus observed is 

 seen to be due to the mutual action of the direct current and 



