fluid conductors when transmitting the electric current. 173 
currents are observed from the point of contact ( at least when 
the mercury is fresh and the contact perfect ) but strong ones 
are always produced, radiating from the other. If it be the 
negative pole which is made to touch, it amalgamates with 
the mercury, which remains bright, and the currents radi- 
ating from the positive are visible to the eye, and generally 
very powerful. On the other hand, if the positive pole be 
in contact, the oxidation of the metallic surface is usually so 
rapid as to prevent the currents becoming visible, but a mo- 
mentary start of the surface from the negative wire, the 
flattening of the globule, and the protuberances it throws out 
in pursuit of the oppositely electrified conductor, sufficiently 
indicate their existence under the crust of oxide. Where 
this oxidation however does not happen, or is prevented by 
the addition of a few drops of dilute nitric acid, the currents 
from the negative wire are equally evident with those from 
the positive, just mentioned. 
19. These however are not the only effects produced by 
contact with the electrified wires. On breaking the contacts 
and completing the circuit in the liquid, the mercury is found, 
for the most part, to have acquired new properties, or lost 
some of its former ones. A globule of four or five hundred 
grains of pure mercury being introduced into a solution of 
sulphate of soda, the circuit was completed in the liquid with 
neither pole in contact. A current was produced from the 
negative pole. A momentary contact being made with that 
wire, and the circuit then completed as before in the liquid, 
a counter-current was produced from the positive pole, more 
confined in the sphere of its extent, but apparently more 
violent in its action than that from the negative. In conse- 
