CHAPTER XIV. 



THE ELECTRICITY OF THE EARTH AND ATMOSPHERE. 



LIGHTNING AND THUNDER. 



FORMATION OF THUNDER CLOUDS. Our investiga- 

 tion of this subject thus far has been confined chiefly 

 to the electricity of the earth and its inductive effect 

 on the atmosphere; we are- now to investigate the elec- 

 tricity of the atmosphere and its inductive effect on the 

 earth. 



We have seen, in the Topler machine, how electric- 

 ity is generated by the mutual friction and induction of 

 insulated conductors, put in motion by mechanical force ; 

 and collected in accumulators which acquire different 

 potentials, and between which a discharge finally takes 

 place, attended with a flash and report. Something 

 analogous to this occurs in the atmosphere. The clouds 

 are large conductors, insulated in the air, moved by the 

 winds, acting inductively on each other and on the 

 earth, and, in other respects, fulfilling the same condi- 

 tions found in the machine. 



As the vapor forming these clouds rises from the earth, 

 it must have, when generated, the same electric potential 

 as that part of the earth from which it rises, and hence 

 the same difference of potential which has been shown 

 to exist in different parts of the earth's surface. 



The air laden with this rising vapor, moving along in 



