Edison Effect in Glow Lamps. 



75 



whether a middle plate offering a surface pierced with many 

 apertures was as effective in producing the current as a solid 



Fiff. 



plate of about the same general outline. Practically it was 

 found that this was the case. 



The magnitude of the currents obtained at various working 

 voltages are of the same magnitude approximately as in the 

 case of a lamp like No. 4, that is to say some 3-4 milliamperes 

 at full incandescence. 



§ 13. A set of experiments was then undertaken with the 

 object of examining the special effect of varying the position 

 of the middle plate, and a series of lamps was used in which 

 platinum or aluminium plates held on platinum wires were 

 placed in the lamp bulb, or in tubes opening into it, in various 

 positions. These lamps are generally 50-volt lamps of usual 

 type, and had single horse-shoe shaped filaments. 



Experiment 10. — A lamp-bulb had a side tube blown on it 

 (see fig. 9) and a plate about 6 centims. long and 1*5 centims. 

 wide welded to a platinum wire was sealed into it. The 

 platinum plate was placed vertically and edgeways in the side 

 tube and the side tube was in such a position that the plane 

 of the platinum plate coincided with the plane of the horse- 

 shoe filament. This lamp, called henceforth No. 2, when 

 worked at 48 volts took 1*3 amperes of current and gave a 

 light of 17*5 candles, equivalent to a power-consumption of 

 3*55 watts per candle-power. The vacuum was very good. 

 In the case of this lamp the current between the positive 

 electrode of the lamp and the platinum plate was found to be 

 numerically very much smaller at the usual working pressure 

 of the lamp than was found to be the case in those lamps in 



