108 WHIRLING MOVEMENTS PRODUCED. 



ranged to descend vertically to the centre of the 



mercury. On transmitting 

 a voltaic current in this 

 circuit of screw-cups and 

 wire to the centre of the 

 Ft. y,.- glass, a whirl of the mer- 



cury is caused by the diverging currents from 

 the centre, with a centrifugal force that caused its 

 subsidence beneath the point of the wire, purposely 

 placed a little below the surface of the mercury. 

 The currents circulated first about the coil sur- 

 rounding the mercury, ascended, and then de- 

 scended to the centre of the mercury, radiating 

 thence as from the centre c ; Fig. 29. The alter- 

 nate breaking of the connection of the circuit by 

 the centrifugal subsidence of the mercury at the 

 centre of the whirl, and the restoration of the 

 level consequent on the stoppage of the current, 

 cause a repetition of this operation intermittently, 

 as often as the current is restored. 



By reversing the direction of the current, the 

 direction of the whirl is reversed. 



The transmission of vertical electric currents 

 to and fro, between the clouds and the horizontal 

 currents from east to west about the earth, excites 

 a revolving motion of the air similar to that of the 

 mercury, and produces whirlwinds or tornadoes; 

 which are always attended with electric discharges. 

 The breeze, or aura, issuing from the point of a 

 wire on the excited conductor of an electric 



