fluid conductors when transmitting the electric current. 171 
so as to insure the transmission of the whole of the electri- 
city developed. The best way is to immerse them in two 
considerable pools of mercury under the acid, one on either 
side of the globule to be set in rotation. 
15. Hitherto we have considered only the effect produced 
when a current of electricity is transmitted over mercury 
through sulphuric acid. When other conducting liquids and 
other metallic bodies are used, phenomena of the same kind 
are produced, but so modified by the nature of the substances 
employed, the intensity of the electric power, and the man- 
ner of conducting the experiments, as to become extremely 
perplexing ; and I must warn the reader who may be inclined 
to repeat them, that he must expect to find them frequently 
fail, or even give contrary results from those I shall describe, 
owing to causes by no means easy to discover. The princi- 
pal is impurity in the mercury used, and none should be used 
but what has been carefully distilled, and well washed with 
dilute nitric acid. It was long before I discovered this 
necessity ; and ignorance of this essential condition engag- 
ed me in a series of tedious and disheartening repetitions 
of every experiment, till I was on the point of relinquishing 
the subject in despair, encountering contradictory results in 
operations conducted, as I then supposed, in a manner pre- 
cisely similar. 
16. When mercury, so purified and perfectly clean, is placed 
in any conducting liquid, and the circuit completed without 
bringing either pole in contact with the metal, the phaeno- 
mena vary with the nature of the liquid ; but, generally speak- 
ing, the effect is the production of currents more or less 
violent, radiating from the point nearest the negative pole. 
