STUDIES IN ATMOSPHERIC ELECTRICITY. 5 



of electricity carried by the ions produced by Röntgen rays, in the 

 following terms. " If the negative ions, say, were to diifer in their 

 power of condensing water around them from the positive, then we 

 might get a cloud formed round one set of ions and not round the 

 other. The ions in the cloud would fall under gravity, and thus we 

 might have separation of positive and negative ions, and the produc- 

 tion of an electric field, the work required for the production of the 

 field being done by gravity." C. T. Iv. Wilson^^ actually found that 

 it requires a greater expansion to produce a cloud on positive ions 

 than on negative ones, and he considers that if ions ever act as 

 condensation nuclei in the atmosphere, it must be mainly or solely 

 the negative ones which do so, and thus a preponderance of negative 

 electricity will be carried down by precipitation to the earth's surface. 

 Elster and GeiteP^ observed that an isolated charged body graduallv 

 loses its electricity when exposed to the atmosphere, the negative 

 electricity being, generally speaking, the more quickly dissipated. 

 They investigated the phenomenon under various circumstances, and 

 came to the conchision that solar radiation or'ives a kind of con- 

 ductivity to the air, by generating in it some minute nuclei capable 

 of carrying electric charges, which they called ions. Of these the 

 negative ions move more quickly than the positive, and soon reach 

 conductors such as the earth's surface, and give up their negative 

 charge, while the positive ions remain and accumulate in the atmos- 

 phere. Thus the usual electric condition of the atmosphere is set up 

 and maintained. Ebert^^ repeated the experiments in balloons and 

 found that the rate of dissipation is greater in the higher altitudes 



1) C.T.R. Wilson, Phil. Trans. 1899. or Nature LXII. p. 149. 1900. 



2) Elster u. Geitel, Terr. Mag. IV. 1899, or Ann. d. Phys. 2. P- 425. 1900. 



3) Ebert, Sitzungsberichte d. inathem.-phys. Classe d. kgl. bayer. Akad. d. W. XXX. p. 

 511, 1900 ; XXXI. p. .35. 1901, 



