87 



The Edison Effect in a " Hylo '" Lamp. 



By Arthuk L. Foley. 



The figure is a cTiagram of a "Hj^lo" turu-down incandescent lamp 

 in which N and s represent (when the current is in the direction indi- 

 cated) the north and south ends respectively of the 16 c.p. filament 

 (F) and the 1 c.p. filament (f), the former consisting of two and 

 the latter of three turns. Whatever be the direction of the current the 

 filament coils are of opposite polarity, the potential difference between 

 legs 3 and 4 is small, and that between legs 1 and 4 a maximum. 

 When f is burning F is in series with it, but the current is insufiicient 

 to render the latter luminous. When F is burning f is short-circuited, 

 but has the same potential as leg 4 of F. 



P 



Let P and P' be points on the globe at the ends of a diameter 

 through the plane of the filaments, and NS and sn be points ' on the 

 globe where the axes of the filaments F and f meet it. At P there 

 is a deposit from one to two cm. wide, while the globe is perfectly 

 clear on either side. At P' the conditions are exactly reversed, the 

 central region being dark with clear glass on each side. At n, also 

 at s, there is a small circular deposit about half the area of a turn 



