CHAPTER VIII. 



ATMOSPHERIC ELECTRICITY. 



Nature has another mode of generating elec- 

 tricity, called atmospheric." The normal con- 

 ditions of potential between the earth and the 

 upper atmosphere seem to be that the atmos- 

 phere is positively electrified and the earth 

 negatively. These conditions change, apv 

 parently from local causes, for short periods 

 during storms. In some way the sun's rays 

 have the power directly or indirectly to give 

 the globules of moisture in the air a potential 

 different from that of the earth. 



In clear weather we find the air near to the- 

 earth in a neutral condition, but gradually as- 

 suming the condition of a positive charge as we 

 ascend ; so that the upper air and the earth are 

 oppositely charged like the two sides of a Ley- 

 <len jar or two leaves of a condenser. This 

 condition is intensified and localized when a 

 thunder-cloud passes over the earth. The 

 moisture globules have h< < -n chaired with po- 

 1 <nergy by the power of the sun's rays 

 when evaporation t<<>k place; hut in this state 

 the energy is neither heat nor electricity, but 

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