Discharges in vacuo. 127 



under the influence of the magnet easily, the tube should be 

 slowly brought near to the magnet from a distance. From 

 what has been said, it follows that these currents possess the 

 ordinary properties of currents, since their deviation is the 

 same as of any conductor whatever conveying a current in 

 the same direction. The action of the magnet upon these in- 

 duced currents agrees completely with the action of the magnet 

 upon the direct current in a highly exhausted space *-, as I 

 have previously found. 



Electrodynamic Actions. 



Goldstein, in the research already quoted, describes certain 

 phenomena which are obtained when the tube is connected at 

 two or more points with the earth. In this case the surfaces 

 of light are not necessarily opposite the points touched, the 

 position of each light-surface is dependent on the magnitude 

 and relative position of the surfaces touched. 



These and all other similar phenomena are easily explained by 

 the mutual electrodynamic action of the currents produced by 

 connecting the different points of the glass surface with the 

 earth. We have in fact to deal with the same action as would 

 be exerted upon each other by currents traversing solid 

 movable conductors. As with these, so also with the induced 

 currents, we observe that similarly directed currents attract 

 each other, and oppositely directed currents repel each other. 

 These experiments were varied in different ways; but all the 

 phenomena are easily explained by the electrodynamic mutual 

 action of the currents produced. 1 will therefore, in what 

 follows, only describe one or two experiments which will 

 justify what has been said. 



The vacuum-tube with the aluminium cross was again em- 

 ployed. When a powerful current was passed through the 

 tube from the coil, the aluminium wire m being the positive 

 pole, then when a was connected 

 with the ground, a fluorescent sur- Fig. 4. 



face appeared on the opposite wall a - 



at o!\ when b alone was touched, the '^ r> V 



fluorescent surface appeared at V\ 



but when both currents were excited 



simultaneously, the fluorescent sur- ~~ 6 



faces approached each other. The 



currents in this case therefore attract each other. The mutual 



attraction can be easily observed by keeping a connected with 



the earth, and alternately making and breaking contact with b; 



* Sitzb. d. k. Akacl, vol. lxxxi. p. 640. 



