214 HENKY A. ROWLAND 



tion I still wish to present to you this theory, which deserves to be 

 thought of in mapping out a system of international experiments on 

 atmospheric electricity. 



Suppose Sir William Thomson's explanation is correct and that the 

 earth is charged with electricity, let us examine what would then 

 happen. If the earth were not exposed to disturbing causes, a portion 

 of the electricity of the globe would discharge itself into the atmosphere 

 and would distribute itself nearly as uniformly as the resistance of the 

 air would allow. The exterior atmosphere thus charged would set itself 

 in motion, and we should have winds produced by the electric repul- 

 sions, and this would last until the electricity had been distributed in a 

 uniform manner on the earth and in the exterior strata of the atmos- 

 phere ; when all would be still once more. An observer stationed on the 

 earth would have no idea of the charge of the exterior atmosphere; but 

 he would discover the charge of the earth by means of the ordinary 

 instruments used in experiments on the electricity of the atmosphere, 

 such as Becquerel's arrows and Thomson's water dropping apparatus. 

 There would be another result which however could not be measured by 

 observers situated on the earth, namely, the extension of the atmos- 

 phere beyond the limits determined by calculation. The rarefied air 

 being electrified would repel itself, and possibly there would be then in 

 the exterior atmosphere a region in which the pressure would vary s T ery 

 slightly for a great difference of elevation. We have learned from 

 auroras and meteors that the atmosphere extends to a much greater 

 distance than that indicated by Newton's logarithmic formula, but I 

 think that what I have said is the first rational explanation of this fact. 



Observe now what would happen if the earth of which we speak were 

 subject to the disturbing causes which exist on our globe; the most 

 important of these disturbing factors are the winds and the general 

 atmospheric circulation. This circulation constantly carries the atmo- 

 sphere from the equator to the two poles, but with very little uni- 

 formity. However, near the poles there must be many points at which 

 the air comes down towards the earth and thus shapes its course towards 

 the equator. Now a body which is a bad conductor, like air, when it is 

 charged tends to carry its charge along with it wherever it goes, and 

 thus the air carries its charge until the moment when it descends 

 towards the earth; then it will leave it behind in the exterior atmo- 

 sphere, in accordance with the tendency of electricity to remain at the 

 surface of charged bodies. The charge will therefore accumulate in the 

 exterior atmosphere, until there is a great tension; the atmosphere 



