III. Atmospheric Electricity in High Latitude.^. 



By GEORGE C. SIMPSON, H.Sc. (18Z1 Exhibition, Scholar of tic I'niverxity 



of Manclicxter). 



Communicated by ARTHUR SCHUSTKI;, F.ft.S. 

 Received February 17, Read March -2, 190;"). 



INVESTIGATION into the problems of atmospheric electricity may be divided into two 

 periods. The first period was devoted almost entirely to measurements of the 

 normal potential gradient in the lower region of the earth's atmosphere, with the 

 aim of finding its daily and yearly variations, its geographical distribution and its 

 dependence on meteorological condition. To this period belongs the fine work of 

 Lord KELVIN and Professor EXNEE.* 



The second period commenced in 1899, when the interest in the problems of 

 atmospheric electricity was at rather a low ebb, owing to the small real progress 

 made during the latter few years. In that year the discovery that atmospheric air 

 is always more or less ionized made at about the same time by ELSTKR and 

 GEiTEt,t in Germany and C. T. R. WlLSONj in England had a completely revo- 

 lutionizing influence on the theories held to account for the earth's normal field. 

 This discovery has brought about a great revival of interest and opened a totally 

 new field for investigation. 



As long as air could be considered a perfect non-conductor EXXEK'S theory that 

 the charge on the earth is a residual charge held a very strong position ; but with a 

 conducting atmosphere it is untenable. An ionized atmosphere means a continual 

 passage of electricity from the charged surface into the highest regions of the atmo- 

 sphere, where only any residual charge could be held. The new discovery having 

 proved conclusively that the charge on the earth is being continuously dissipated 

 into the ionized air above, it became of prime importance to determine the rate 

 at which the electricity is dissipated and the conditions under which the loss 

 takes place. 



The first serious attempt to do this was made by ELSTER and GEITEL. They 

 designed an instrument consisting of a charged cylinder exposed to the air 



* For a good resumf of this period see EXNER, ' Terr. Mag.,' vol. 5, p. 167, 1900. 

 t 'Phys. Zeit.,' 1, p. 245, 1899; 'Phys. Zeit.,' 2, p. 116, 1900. 

 \ <-Roy. Soc. Proc.,' 68, p. 151, 1901. 



'Phys. Zeit.,' 1, p. 11, 1899; 'Terr. Mag. and Atm. Elect.,' 4, p. 213, 1899; ' DRUDE'S Aim.,' 2, 

 p. 425, 1900. 



VOL. COV. A 389. 28.7.05 



