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THE POPULAR SCIENCE MONTHLY. 



turns. I arrange the magnet to draw the molecular stream so as to 

 beat against the upper vanes, and the wheel revolves rapidly as if it 

 were an overshot water-wheel. I turn the magnet so as to drive the 

 radiant matter underneath ; the wheel slackens speed, stops, and then 



begins to rotate the other way, like an undershot water-wheel. This 

 can be repeated as often as I reverse the position of the magnet. 



I have mentioned that the molecules of the radiant matter dis- 

 charged from the negative pole are negatively electrified. It is prob- 

 able that their velocity is owing to the mutual repulsion between the 

 similarly electrified pole and the molecules. Tn less high vacua, such 

 as you saw a few minutes ago (Fig. 16), the discharge passes from one 

 pole to another, carrying an electric current, as if it were a flexible 

 wire. Now it is of great interest to ascertain if the stream of radiant 

 matter from the negative pole also carries a current. Here (Fig. 18) 



is an apparatus which will decide the question at once. The tube con- 

 tains two negative terminals {a, h) close together at one end, and one 

 positive terminal (c) at the other. This enables me to send two streams 

 of radiant matter side by side along the phosphorescent screen, or, by 

 disconnecting one negative pole, only one stream. 



