fluid conductors when transmitting the electric current. 1 65 
ultimately falls into and amalgamates with it, like a body 
acted on at once by an attractive force tending to the nega- 
tive, and a repulsive, from the positive wire. 
7 . These apparent attractions and repulsions, this elongation 
of large masses of mercury and bodily motion of small ones 
toward the negative pole, are in reality, however, only se- 
condary effects ; their immediate cause, as well as that of the 
currents in the surrounding acid, will be discovered by a 
more minute attention to what takes place in the mercury 
itself, while under the influence of the electric action. 
8 . To this end, if we operate on a considerable mass of 
mercury, and, instead of covering it with the acid, merely 
moisten it and the containing vessel, making the circuit as 
before, only by the medium of the thin film of acid which 
adheres, the circulation of the mercury will be not less vio- 
lent ; but it will then be evident that the origin of the motion 
is in the mercury itself, the acid film being (so far as mecha- 
nical impulse is concerned ) merely passive, and dragged 
along by its adherence to the mercury, coating it frequently 
with a stratum so thin as to reflect iridescent colours over 
its whole surface, and render the phasnomenon extremely 
beautiful. The motion of the mercury consists in a conti- 
nual radiation of its superficial molecules from the point 
nearest to the negative pole, by which it is kept in a con- 
stant state of circulation, each particle being urged along the 
surface from the negative to the positive pole and returning 
along the axis. Were the mercury insulated from contact 
with the bottom of the sustaining vessel, and devoid of adhe- 
sion to the liquid, the momentum of the portions going and 
