Edison. Effect in Glow Lamps. 



11 



If we compare together the results obtained with this 

 lamp No. 2, in which a plate is placed edgeways on and 

 outside the carbon loop, with the results obtained in the case 

 of lamp No. 3, in which the plates embraced the carbon in 

 the form of cylinders, we see the difference produced by the 

 change of position of the plate. Both these lamps, No. 2 and 

 No. 3,are48-volt lamps when working at normal incandescence. 

 Referring to Table No. 7 in § 7, we see that for lamp No. 3 

 at -48 volts the voltage difference of the positive electrode and 

 the platinum cylinders was respectively 13*2 and 18*3 volts 

 as measured with the Elliott galvanometer, and this indicated 

 a current of about 1*3 and 1*8 milliamperes flowing through 

 the resistances from the positive lamp electrode to the metal 

 plate ; but in the case of lamp No. 2, at 48 volts the potential- 

 difference between the platinum plate and the positive lamp 

 electrode was only *2 volt, and this corresponded to a current 

 of *03 milliampere nearly. Accordingly the current is greatly 

 diminished when the collecting-plate is placed edgeways to 

 and someway outside the loop of the carbon. At normal 

 incandescence the current between the positive lamp electrode 

 and the middle plate when joined by the galvanometer is 

 about -03 or '04 milliampere when the positive leg of the 

 carbon is nearest the middle plate, but only about *02 or *03 

 milliampere when the negative leg is nearest the plate. 



§ 14. Experiment 11.— In order to compare the previous 

 results just given with those obtained when the collecting- 

 plate was placed broadside to and yet outside the carbon loop, 



Fig. 10. 



a lamp was made as in fig. 10 in which an aluminium plate 

 was held on a platinum wire just outside one leg of the 



