THUNDER AND LIGHTNING. 



ductors or paratonnerres for the protection of buildings. 22. Effects 

 of lightning on bodies which it strikes. 23. The Aurora Borealis 

 the phenomena unexplained. 24. General character of the 

 meteor. 25. Description of auroras seen in the polar regions by 

 M. Lottin. 



1. THERE is DO part of physical science in which the researches 

 of modern investigators have been attended with such signal 

 success, as those which have been directed to the discovery of the 

 influence of electricity* upon the atmosphere. Indeed it would be 

 difficult to name any atmospheric change, which is not directly or 

 indirectly connected with electric- agency. It is true that these 

 atmospheric phenomena, fugitive and transitory as most of them 

 are, have not been in all cases traced with clearness and cer- 

 tainty to their causes, that the relation of some of them to the 

 agency of electricity is rendered probable, more from general 

 appearances than by distinct and satisfactory demonstration, and 

 that some of them, which are evidently of electric origin, have, 

 nevertheless, remained unexplained by, or not reduced to, any of 

 the known laws which govern that physical agent. Still there is 

 much that falls under the general principles of electric science, 

 and those phenomena which remain with or without any satis- 

 factory explanation require to be stated, that those who 

 pursue this part of physical science, with a view to extend its 

 limits, may be guided to proper subjects of observation and 

 investigation. 



How important the topics embraced under the general head of 

 atmospheric electricity are, will be understood when it is stated, 

 that upon the electric condition of the atmosphere, and the 

 changes incidental to it, depend not only the stupendous phe- 

 nomena of thunder-storms, but also the whole of that beautiful 

 and interesting class of phenomena comprised under the general 

 name of Aurora Borealis. 



2. The terrestrial globe which we inhabit is invested with an 

 ocean of air, the depth of which is about the 200th part of its 

 diameter. It may, therefore, be conceived by imagining a coat- 

 ing of air, the tenth of an inch thick, investing a twenty-inch 

 globe. This aerial ocean, relatively shallow as it is, at the 

 bottom of which the tribes of organised nature have their 

 dwelling, is, nevertheless, the theatre of stupendous electrical 

 phenomena. 



It may be stated as a general fact, that the atmosphere which 

 thus covers the globe is charged with positive electricity, which, 

 acting by induction on the superficial stratum of the globe on 

 which it rests, decomposes the natural electricity, attracting the 

 negative fluid to the surface and repelling the positive fluid to 

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