92 



Prof. J. A. Fleming on the 



however, the shielded leg or leg enclosed in the glass tube 

 was made the negative leg, which could be done by reversing 

 the current through the carbon conductor, then the condenser 

 was not discharged when its positive plate was connected 

 with the middle plate. 



The same fact was less perfectly exhibited by employing 

 the lamp with the middle plate having a removable mica 

 shield on one side. We are thus able to assure ourselves that 

 the active agent in producing this discharging effect upon a 

 positively charged body connected to the middle plate is the 

 negative leg of the carbon conductor. The experiments were 

 varied in many ways, but all pointed to the conclusion that if 

 a charged condenser is connected to two terminals, one of 

 which is a metal plate and the other a carbon conductor, both 

 enclosed in a high vacuum but yet separated from each other 

 by an inch or so of distance, the condenser is discharged 

 instantly when the carbon terminal is rendered highly 

 incandescent, provided that the negative plate of the con- 

 denser is in connexion with it. 



§ 23. If the condenser is left in contact with the middle 

 plate under some circumstances, not only is it discharged if 

 previously charged but is charged again in an opposite 

 direction. 



Experiment 20. — A condenser of 5 microfarads capacity 

 perfectly discharged has its poles or terminals connected for 

 one instant, one with the middle plate of No. 4 lamp and the 

 other with the positive electrode of the lamp (see fig. 18). 



On removing it and testing it with the galvanometer Gr it is 

 found that the condenser plate in connexion with the middle 

 plate of the lamp has received a negative charge and the 

 other plate of the condenser a positive charge. 



