POTENTIAL AND EARTH CURRENTS. 183 



The rarefying of the air from heat, at the time of the 

 morning maximum, must increase and accelerate the as- 

 cending current, while its condensation from cold, at the 

 evening maximum, similarly affects the descending cur- 

 rent ; gravity in each case supplementing electric force. 



COSMEC ELECTRIC INFLUENCE. Assuming that 

 electricity is a universal force, acting through matter 

 in different forms, as a universal medium, it follows 

 that electric induction is universal. Hence induction 

 between our planet and the other members of the solar 

 system, especially the sun and moon, must affect the 

 electric condition of the earth and atmosphere. 



It is considered a well established principle, that the 

 tides are due to the attraction of the sun and moon, 

 attributed to gravity. But the daily electric maxima 

 and minima indicate that there are electric tides, coin- 

 cident with the ocean tides, due to the electric induc- 

 tion of the sun and moon : that an electric impulse 

 follows the earth's movement, as different portions of 

 its surface are successively exposed to this influence 

 during its daily rotation, producing electric currents 

 in both the land and water surface ; and perhaps also 

 tidal waves in the ocean and atmosphere. 



We have seen that when a charged sphere is placed 

 near the end of a cylinder, or of the longer axis of a 

 spheroid, the electricity of the cylinder or spheroid is 

 either repelled or attracted by induction, according as 

 the potential of the sphere is positive or negative, \vith 

 reference to that of the other body ; and that this effect 

 is intensified when two charged spheres, at different 

 potentials, are placed at opposite ends of the cylinder, 

 or longer axis of the spheroid. If both are placed at 

 the same end, the inductive effect is a mean between 



