On tlie Origin of Meteoric Stones. 83 



perhaps, serve as a recommendation to our hypothesis, that, 

 being received as the true one, it appears to throw light on a 

 very dark subject — the origin and changes of the electricity of 

 the atmosphere. For, if the extremely minute volatile particles 

 of solid bodies ascend without mixture, and with extreme rapi- 

 dity, on account of their lightness, through the under strata of 

 air, both the most powerful means of exciting electricity — 

 friction of conducting and nonconducting bodies, and contact of 

 heterogeneous substances, are in constant operation during their 

 motion upwards. Hence the change of the electricity of the air. 

 And since a highly rarified air is a good conductor for both 

 kinds of electricity, it appears natural, that, m the superior 

 regions, sometimes the one and sometimes the other may accu- 

 mulate, till they have acquired sufficient force to produce great 

 effects. These effects may be of very different kinds, either ac- 

 cording to the variety of vapours which may have assembled in any 

 particular space, or the different nature of the excited electricity. 

 Philosophers almost with universal consent hold the Northern 

 Lights for electrical phenomena ; our hypothesis would shew 

 that the so-termed artificial aurora, is, in reality, similar to the 

 natural, and it appears even to assign the reason why these 

 phenomena chiefly predominate in the polar regions. Since, in 

 tbe lower strata of air, where our electrical experiments are con- 

 ducted, only an inconsiderable portion of the exhalations from 

 solid bodies is contained, it is not improbable that these lumi- 

 nous appearances take place only when the electricity is accumu- 

 lated in a comparatively pure rarified atmosphere, to which, on 

 the contrary, heterogeneous mixtures are unfavourable. Unques- 

 tionably, however, the atmosphere in the polar regions is freer 

 from exhalations from sohd bodies, than in the temperate and 

 torrid zones ; partly because, in the colds of the north, exhala- 

 tions go on slower, and in less quantity ; partly because there 

 the under strata of air are almost exclusively in contact with 

 water and ice ; and partly, in fine, because there, there is little or- 

 ganic life, little corruption or combustion. We are, therefore, 

 entitled to assume that, above the Polar zones, the higher re- 

 gions of the atmosphere are extremely pure, since, during in- 

 tense degrees of cold, only a very small quantity, even of aque- 

 ous vapour, can be generated. Metallic and earthy exhalations 



r 2 



