MEMOIR XXVI. J CAPILLARY ATTRACTION, ETC. 



349 



Fig. 72. 



Fig. 73. 



indicated by the dotted line, and currents also are seen 

 playing in the water. If the neg- 

 ative wire be introduced into the ^c. 

 centre of the metallic globule, and 

 the positive be- brought on one 

 side, as in Fig. 73, the mercury will bulge out elliptically 



at both sides, nearest and farthest 

 from the positive pole. If, now, 

 the negative wire be cautiously 

 raised from its position, so as to 

 be just out of contact with the surface of the metal, the 

 mercury is immediately convulsed, its whole surface be- 

 ing covered with circular waves. On lowering the neg- 

 ative wire to its former position and advancing the posi- 

 tive, the moment it conies to the edge of the mercurial 

 ellipsoid intense convulsions are produced, which increase 

 until contact of the mercury and wire takes place. 



At the same time that these movements are going on 

 in the mercury, the surface of the water is ploughed by 

 gentle currents, exactly resembling those that might be 

 produced by directing a stream of air 

 from a blow-pipe slantingly across the 

 surface (Fig. 74). 



The following experiment illustrates 

 the nature of these effects : 



A platinum needle, a c, Fig. 75, is suspended by a 

 thread of unspun silk from a stand, b b, 

 in a cup filled with acidulated water as 

 high as d d. The needle hangs hori- 

 zontally, its ends being about one fourth 

 of an inch distant from the platinum 

 polar wires, p, n, of a battery. Now the 

 wire p being positive and n negative, 

 the extremity a of the suspended nee- 



Fig. 74. 



Fig. 75. 



die would be negative and c positive 



