$6 



Prof. J. A. Fleming on the 



the positive leg the current is greatly diminished, both by 

 reason of the fact that it opposes less surface to the negative 



Fig. 15. 



leg, and also because the middle plate acts as a shield between 

 it and the negative leg of the carbon. 



§ 19. Experiment 17. — In order finally to demonstrate 

 that the negative leg of the carbon loop was the chief active 

 agent iu this production of a current between the middle 

 plate and the positive electrode, a lamp like No. 4 was taken 

 having a metal middle plate between the legs, and this middle 

 plate had attached to it a mica screen (see fig. 16) a little 



Fig. 16. 



MIDDLE PLATS SHIELDED 



MIDDLE PLA TE EXPOSED 



larger than the plate, and so fixed by a loose rivet that it 

 could be shaken in front of the plate so as to shield one side 

 of it, or shaken on one side so as to fully expose the plate. 

 This device was in fact a removable shield attached to one 



