u 



THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[SIXTH SERIES.] 



MA Y 1910. 



LXXI. The Effect of Dust and Smoke on the Ionization of 

 Air. By A. S. Eve, ALA., B.Sc., McGill University, 

 Montreal *. 



A LARGE number of observers, using the instrument, or 

 ion-counter, devised by Ebert, have found a considerable 

 excess of positive over negative ions in the atmosphere. The 

 ratio of the number of positive to the number of negative 

 ions has been found to vary much with meteorological and 

 local conditions, but the mean value 1*17, obtained by 

 Simpson f in Lapland during a year's continuous observa- 

 tions, may be taken as a fair average result. The number of 

 ions of each kind per cm. 3 in the atmosphere is of the order 

 1000 to 2000, so that an excess of 17 per cent, corresponds 

 to a numerical excess of the order 200 per cm. 3 



Now, if an excess of this magnitude were maintained for a 

 height of 4 kilometres, the positive charge in the air would be 

 4xl0 5 x200x4'6xl0- 10 or '6-7 x 10" 2 E.S.U. per cm. 2 of 

 the earth's surface. This would be far more than sufficient, 

 indeed 75 times too great, to balance the corresponding- 

 negative charge on the earth's surface, which has been found 

 by C. T. R. Wilson to be of the order 5xl0~ 4 E.S.U. 

 per cm. 2 



Doubtless, as the results of balloon ascents prove, the 

 distribution of electricity is different at various altitudes, and 



* Communicated by the Author, 

 t Phil. Trans. A, ccv. (1905). 



Phil Mag. Ser. G. Vol. 19. No. 113. May 1910. 2 U 



