MEMOIR XXVI.] CAPILLARY ATTRACTION, ETC. 



separating them. And the reason is obvious, for the 

 glass has brought away with it a layer of water, and 

 there has been no true separation of the solid from the 

 liquid, but only of water from water. The force of ad- 

 hesion of the glass to the water has exceeded the cohe- 

 sion of the water for itself. 



If a plate of polished zinc be laid on mercury, there 

 will, again, be no electrical development apparent on 

 separating them. For, owing to the conductibility of 

 the zinc, there is nothing to prevent the opposite elec- 

 tricities from uniting, and all electrical manifestations 

 must cease. 



Whatever can disturb the electrical relations of a 

 solid and a liquid will disturb their capillarity. On 

 wetting the interior of a glass tube, so as to form a tem- 

 porary tube of water, and placing some mercury in it, 

 the mercury will be depressed below the hydrostatic 

 level. But on connecting the mercury with the negative 

 pole of a voltaic battery, and the water with the posi- 

 tive, the mercury at once rises, their mutual attraction 

 being increased. 



I derived these conclusions from the following experi- 

 ments : 



1. In a watch-glass (Fig. 70) place a quantity of pure 

 mercury, a &, and upon it a drop of water, c. Bring the 

 water in contact with the positive 

 platinum electrode of a voltaic bat- 

 tery, and touch the mercury with 

 the negative. The moment the con- 

 tact is made the drop of water Fig. 70. 

 loses its spherical form and spreads out into a thin cir- 

 cular disk, wetting the surface of the mercury. The di- 

 ameter of the disk seems to be greater in proportion as 

 the battery is more powerful. 



Under ordinary circumstances water does not wet 



