1885.] Glow-Lamps raised to High Incandescence. 



219 



II. " On a Peculiar Behaviour of Glow-Lamps when raised to 

 High Incandescence." By William Hexry Preece, F.R.S. 

 Received March 18, 1885. 



1. During my recent visit to America (October, 1884) Mr. Edison 

 showed me a very striking experiment with glow-lamps, the prin- 

 ciple of which he had not threshed out, although he had attempted to 

 apply it practically to the regulation of the current flowing in electric 

 light circuits. 



Fig. 1. 



If abc be the incandescent filament of a glow-lamp, de a thin 

 narrow platinum plate fixed between the limbs of the filament with 

 an independent wire connexion ee' sealed in the glass globe, then, if 

 a galvanometer Gr be connected between a, the positive electrode, and 

 e, a derived current will be observed to pass through G, and through 

 the rarefied space ec when the main current is increased to a certain 

 strength, and the filament reaches a certain degree of incandescence. 

 The strength of this derived current will increase with the increased 

 brilliancy of the glowing filament. Mr. Edison made for me several 

 lamps of different forms and character to enable me to investigate 

 the phenomenon more carefully in England, and I have the pleasure 

 of submitting the results of those experiments to the Society. 



Q'2 



