Edison Effect in Glow Lamps. 



83 



So far the results are quite normal, and if the results in the 

 above Table No. 12 are compared with those in Table 2 for a 

 similarly constructed lamp with no tubular shield we find that 

 the magnitude of the current flowing from the positive elec- 

 trode to the middle plate is in the two cases very much the 

 same. The lamp No. 9 was then placed on the circuit in such 

 a manner that the leg shielded by the glass tube was the 

 negative leg, and a similar series of observations of the current 

 between the positive leg (now the uncovered leg) and the 

 middle plate was made. The results were as follows in Table 

 No. 13 :■— 



Table No. 13. Lamp No. 9. Milamperemeter. 



Table showing the potential-difference between the middle 

 plate and positive electrode, and the current flowing 

 through a galvanometer connecting them, when the 

 negative leg of the carbon is shielded in a glass tube. 



Working volts of 

 the lamp. 



Potential -difference 



of middle plate and 



positive electrode in 



-volts. 



Milliampere 



current through 



gahanometer. 



45 



47 

 49 

 51 



•10 

 •15 

 •25 

 •30 



•016 

 •024 

 •039 

 •044 



On comparing the results in Table No. 13 and the previous 

 one No. 12 we see what an immense reduction in the current 

 flowing between the positive electrode and the middle plate is 

 produced by shielding the negative leg. Hence the action in 

 virtue of which the current is produced is greatly interfered 

 with by enclosing or covering up the negative leg of the 

 carbon. In this particular case at 51 volts, the current 

 between the positive electrode of the lamp and the middle 

 plate when the negative leg is covered up is only -g 1 ^ of that 

 which it is when the positive leg is covered up. The results 

 in Tables Nos. 12 and 13 are plotted together in Curve No. 6. 



G2 



