126 Dr. K. Domalip on Alternating 



by connectiDg the upper surface of the side tube with the 

 earth. Then, as we know, these currents are propagated in 

 straight lines from the surface touched and strike the opposite 

 wall, producing a fluorescent surface. The production of this 

 fluorescent surface much facilitates the investigation into the 

 action of the magnet, since it is only necessary to observe the 

 motion of the fluorescent surface in order to infer the motion 

 of the current producing it. In some cases the rays issuing 

 from the points touched are visible; but in other cases they 

 are not. 



The action of the magnet in the equatorial position was 

 first investigated. For this purpose the tube was so placed 

 between the poles of the magnet that the line joining the 

 point touched with the fluorescent surface on the opposite 

 wall was at right angles to, and bisected, the line joining 

 the two poles. When the magnet was excited, the fluorescent 

 surface, and with it the current producing it, would move 

 upwards or downwards according to the polarity of the magnet. 

 Closer examination showed that the deviation could be deter- 

 mined by assuming that the negative current moved in a 

 straight line from the point touched to the opposite wall, and 

 that consequently the positive current is propagated in the 

 opposite direction. Hence, applying Ampere's rule, we can 

 easily explain the motions observed. 



Next, the magnetic action was investigated when the cur- 

 rent was placed axially: the tube was moved along in the 

 axial position, so that the current was first over the one 

 pole; then, on moving the tube further, it came into the 

 neutral point, and then over the other pole. In every case the 

 motion of the fluorescent surface, and consequently of the 

 current, could be predicted from Ampere's rule. 



It is not, therefore, necessary to describe the different cases ; 

 but I will proceed to describe another experiment. 



When the side tube of the vacuum-tube, already described, 

 is touched at two different points, 

 a and b, two intersecting currents Fig* 3. 



will be produced; V is the fluores- 

 cent surface caused by the current 

 proceeding from b, and a! that pro- 

 duced by the current from a. When 

 this tube is placed equatorially be- 

 tween the poles of the magnet, the 

 fluorescent surfaces are displaced 

 in opposite directions on the glass wall, in accordance with 

 Ampere's well-known rule. 



I will further remark that, in order to observe these motions 



