88 



of f. This deposit is surromidetl l)y another in the furni of a ring about 

 1 tm. Avide and 2 cm. in diameter, the ring being oi)en next the base 

 of the lamp. Between the central deposit and tlie ring the glass is 

 clear. There is no deposit within 2 cm. of the base of the lamp, and 

 very little on the crown. 



The theory of molecular shadows and the Edison Effect, so thor- 

 oughly worked out by Fleming* and others, explains the general char- 

 acter of the deposit, but seems to fail to explain the definiteness of 

 it. In general the deposit is of uniform density and quite dark, while 

 the clear places are perfectly clear, the line of separation being as 

 definite as if the deposit had been laid on with a brush. 



The weak magnetic teld of the small filament was sufficient to 

 concentrate the deposit at the ends of its axes, leaving certain regions 

 perfectly clear. It seems that it should be possible to keep clear any 

 desired part of the wall of a vacuum tube. 



The peculiarity of the deposit above described was noticed but a 

 few weeks since, hence the incompleteness of this investigation. An 

 attempt to age a number of similar lamps by running at an excessive 

 voltage resulted in a practically uniform deposit. 



"■'.Molecular Shadows in Incandescent Lamps. Philofophical Magazine, Vol. 20, 1885. 

 A Further Examination of the Edison Effect in Glow Lamps. Philosophical Magazine, 

 Vol.42, 1896. 



