428 Prof. E. Edlund on Atmospheric Electricity 



the charge of the body. In the regions of the terrestrial sur- 

 face where the force of induction is either zero or very little, 

 the body will in consequence more readily lose its electric 

 charge than in the localities where that force is greater ; the 

 conductivity of the moist air will therefore appear greater in 

 the polar regions than at lower latitudes. The composition of 

 pure air is, without any doubt, the same in the frigid as in the 

 temperate zone ; . at the same temperature and under the same 

 pressure it must in both regions contain, when saturated, the 

 same quantity of aqueous vapour : and it is impossible to dis- 

 cover any reason for which its electric conductivity should be 

 different. It is, therefore, to exterior causes that we must at- 

 tribute the rapid loss of the charge of electrified bodies in the 

 polar regions ; and the exterior causes are probably those which 

 have just been indicated. 



According to the proposed theory it is self evident, without 

 any other explanation, that the air would, as was proved by 

 the observations of M. Wijkander, exhibit traces of positive 

 electricity on the days distinguished by intense aurorse 

 bore ales. 



The cause just given for the electric state of the atmosphere 

 is probably the only one which acts uninterruptedly every- 

 where ; but no doubt there exist others, the action of which, 

 connected wdth certain localities, is of a more accidental cha- 

 racter. To these belong, for instance, the development of 

 electricity described by M. K.-A. Holmgren, who found that, 

 on the division of a liquid into drops, an electromotive force 

 arises at the point itself where the division is effected *. To 

 the same force is probably due the negative electricity of the 

 fine drizzle carried away by the air in cascades or powerful 

 cataracts. As to evaporation, vegetation, the friction of the 

 molecules of the air against one another or against the surface 

 of the earth, as w r ell as several other phenomena in which some 

 have been willing to trace the cause of the electricity of the 

 air, they have assuredly no sensible influence upon the pheno- 

 menon in question f. Of course, however, if clouds in the 



* lt De l'Electricite coinme Force cosrnique," par K.-A. Holmgren, 

 Memoires de V Academic des Sciences, t. xi. (1872). 



t Of all those so-called causes of the electricity of the air, and of the aurora 

 borealis, evaporation is, -without doubt, that which has attracted most 

 notice ; but manifold reasons may be cited for the opinion that evapora- 

 tion has nothing to do with this phenomenon. We may observe, in the 

 first place, that no one has ever succeeded in definitively proving, by ex- 

 periments made in the laboratory, that evaporation produces electricity. 

 This opinion, therefore, is not founded on a solid basis of experiment. 

 Further, according to this opinion the electricity of the air ought to be 

 more intense in summer than in winter, seeing that the evaporation is 



