Febbuabt 5, 1904.] 



SCIENCE. 



205 



the axes of the filaments F and / meet it. 

 At P there is a deposit from one to two 

 centimeters wide, while the globe is per- 

 fectly clear on either side. At P' the con- 

 ditions are exactly reversed, the central 

 region being dark with clear glass on each 

 side. At n, also at s, there is a small circu- 

 lar deposit about half the area of a turn of 

 /. This deposit is surrounded by another 

 in the form of a ring about one centimeter 

 wide and two centimeters in diameter, the 

 ring being open next to the base of the 

 lamp. Between the central deposit and 

 the ring the glass is clear. There is no 

 deposit within two centimeters of the base 

 of the lamp, and very little on the crown. 

 The theory of molecular shadows and the 

 Edison effect, so thoroughly worked out by 

 Fleming* and others, explains the general 

 character of the deposit, but seems to fail 

 to explain the definiteness of it. In gen- 

 eral the deposit is of uniform density and 

 quite dark, while the clear places are per- 

 fectly clear, the line of separation being as 

 definite as if the deposit had been laid on 

 with a brush. The weak magnetic field 

 of the small filament was sufficient to con- 

 centrate 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 table. The peculiarity of the de- 

 posit 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 prac- 

 tically uniform deposit. 



On the Charges given to Surfaces hy the 

 Diffusion of Ions, and the Earth's Nega- 

 tive Potential: John Zeleny, University 

 of Minnesota. 



* ' Molecular Shadows in Incandescent Lamps,' 

 Philosophical Magazine, Vol. 20, 1885. 'A Fur- 

 ther Examination of the Edison Effect in Glow 

 Lamps,' Philosophical Magazine, Vol. 42, 1896. 



Experiments are described showing that 

 neutral ionized air in passing through a 

 long tube at first gives a negative charge 

 to the walls, but as it passes along it 

 eventually gives them a positive charge. 

 In passing through a short tube the ionized 

 air acquires a positive charge, while the 

 tube itself becomes charged negatively. 

 Similar effects were obtained with dry car- 

 bonic acid, but when the gas was saturated 

 with water vapor the effects were all re- 

 versed in sign. The experiments are all 

 explained by supposing the charges to arise 

 from the unequal rates of diffusion of the 

 two ions. It is shown that Villari's hy- 

 pothesis that charges are given to metals 

 by the friction of the ionized gas against 

 the -metal does not suffice to explain all of 

 the facts. Simpson's objection to Geitel's 

 explanation of the earth's negative po- 

 tential is next taken up and the results of 

 the above experiments are used in refuta- 

 tion of the objection. Other theories of 

 the cause of the earth's negative potential 

 are briefly considered. 



The Rate of Propagation of Smell: John 

 Zeleny, University of Minnesota. 

 The propagation of smell through tubes 

 where the air is free from convection cur- 

 rents was found to be very slow, as has 

 already been noted by Ayrton; showing 

 that the fast propagation ordinarily ob- 

 served in free space is due almost entirely 

 to convection currents. For example, with 

 ammonia diffusing through a tube a meter 

 and a half long, over two hours elapsed 

 before the smell could be detected at the 

 other end of the tube. Using different 

 lengths of tubing, it was found that the 

 time required for the diffusion of the smell 

 was roughly proportioned to the square of 

 the length. Ammonia and hydrogen sul- 

 phide were used for the above experiments. 

 The presence of ammonia could be detected 

 chemically at a point in a tube after about 



