Nipher—On the Nature of the Electric Discharge. 3 



famous experiment on the electromagnetic effect due to 

 the motion of a charged body, establishes the fact that a 

 positively charged body, moving in space, produces the 

 same electromagnetic field as a negatively charged body 

 moving along the same path with equal velocity in the op- 

 posite direction. These two actions are, however, not 

 identical, since they involve the motion of masses of mat- 

 ter in opposite directions. 



The positive luminiscence in the Geissler tube is not 

 necessarily a discharge of positive electricity, although 

 it seems to proceed from the positive terminal. J. J. 

 Thompson found that this positive luminescence in a tube 

 15 meters in length moved outward from the positive 

 terminal, with a velocity somewhat more than half that of 

 light. But this may only be a result of the negative dis- 

 charge. A stream of water issuing with great velocity 

 from a pipe may wear a channel into the earth, and this 

 channel may lengthen for a time in the direction of flow. 

 At a distant point where this stream runs down a steep 

 bank into the sea, a channel may also be worn, which may 

 elongate indefinitely in a direction opposite to that in 

 which the stream flows. The gradual recession of the 

 falls of Niagara is an illustration of such action. 



If the water were invisible, and if the recession of 

 Niagara Falls from Lake Ontario to Lake Erie should 

 occur in ten minutes, the phenomenon might be thought 

 to be a "positive discharge" into Lake Erie. 



The positive luminescence in Thomson's long tube may 

 be explained as follows: 



The ironization of the column of gas at the anode end 

 begins at the anode wire. Negative particles pass from 

 molecules in contact with it to the wire. These molecules 

 thus ironized are then capable of accepting negative par- 

 ticles from their neighbors who are slightly more remote 

 from the anode. In other words, they have acquired the 

 property of conduction. It is as though the length of the 

 anode wire had been extended into the tube. In the lan- 

 guage of the two-fluid theory, positive electricity has be- 



