Edison Effect in Glow Lamps. 81 



eighteen inches from the incandescent conductors practically 

 extinguishes the phenomenon. 



Experiment 13. — Another similar bulb was provided having 

 a side tube blown on it of half the length, viz. about 9 inches 

 long. At the end of this tube was placed a small aluminium 

 plate as before, and the tube was bent up about the middle at 

 right angles (see fig. 12). When the carbon conductor in 



Fin-. 12. 



r~^\ 



the bulb, which was that of an ordinary 50-volt 16 candle- 

 power lamp, was rendered incandescent by being connected 

 to a circuit of appropriate electromotive force, and the Elliott 

 galvanometer connected in between the aluminium plate and 

 the positive electrode of the lamp, a current of not more than 

 about one twenty-thousandth of a milliampere was detected. 

 The fact that the " Edison effect" was extinguished when the 

 collecting-plate was placed at the extremity of an elbow-tube 

 was first observed and recorded by Mr. Preece. 



§ 16. The effect of position and size of the plate having 

 been examined, the next step which naturally suggested itself 

 was to determine the effect of the different portions of the 

 incandescent conductor in the production of it. 



Experiment 14. — A lamp like No. 4 was provided, but in 

 which one leg of the carbon was enclosed in a glass tube of 

 the size of a quill. The glass tube was sealed on to the 

 platinum wire and extended nearly up to the bend of the 

 carbon (see fig. 13). This lamp, called No. 9, was placed on 

 the circuit in such a manner that the shielded leg was the 

 Phil. Mag. S. 5. Vol. 42. No. 254. July 1896. G 



