PROCEEDINGS OF THE ACADEMY AND AFFILIATED 



SOCIETIES 



THE PHILOSOPHICAL SOCIETY OF WASHINGTON 



The 759th meeting was held at the Cosmos Club, on October 2, 1915. 

 President Eichelberger in the chair, 70 persons present. 



Mr. W. F. G. Swann presented a paper on The normal electric field 

 of the Earth. The first portion of the paper dealt with the causes 

 responsible for the ionization of the atmosphere. The radio-active 

 material in the air over the sea is not sufficient to account for the 

 ionization observed, l)ut the measured value of the penetrating-radia- 

 tion is amply sufficient to make up for the deficit. Over the land the 

 active material in the air above is sufficient to account for more than 

 the ionization ordinarily observed, so that there is a surplus to account 

 for the existence of a large number of the so-called "Langevin ions." 



The second portion of the paper dealt with the maintenance of the 

 Earth's charge. It was shown, on theoretical grounds, that the as- 

 sumption of a continual return conduction current over some region 

 of the Earth is untenable. Any theory which accounts for the mainte- 

 nance of the Earth's negative charge by the entrance of negative 

 corpuscles from regions outside the atmosphere, will, in virtue of the 

 known increase of conductivity with altitude, automatically account 

 for the positive charge in the atmosphere. 



It was explained that if any theory is adopted in which the negative 

 charge on the Earth comes in some way from the atmosphere, and in 

 which the replenishment is confined to a limited region or time, then, 

 on such a theory it is necessary to assume a state of very high con- 

 ductivity in the upper atmosphere in order to account for the existence 

 of atmospheric-electric phenomena at places where the replenishment 

 is absent. 



The part played by the electrical convection current was considered, 

 and it was explained that any attempt to account for a balance of the 

 conduction current by this agency would result in the conclusion that 

 all atmospheric-electric phenomena should , be located within a shell 

 of comparatively small altitude. 



The significance of the variation of the vertical conduction current 

 with altitude was discussed, and it was pointed out that such variations 

 indicate a passage of electricity into and out of the volume-elements 

 of the air partly by processes other than conduction. A provisional 

 hypothesis as to a corpuscular emission from the atmosphere was 

 cited, by the help of which such variations in the vertical conduction 



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