On the magnetic Phenomena produced by Electricity. 407 
solution of this kind, placed in the Voltaic circuit, gain any po- 
larity; and the only proof of the magnetic powers of electricity 
passing through such a fluid, was afforded by its effect upon the 
magnetized needle, when the metallic surfaces, plunged in the 
fluid, were of considerable extent. ‘That the mobility of the 
parts of fluids did not interfere with their magnetic powers as 
developed by electricity, I proved, by electrifying mercury, and 
Newten’s metal fused, in small tubes. These tubes, placed in 
a proper Voltaic circuit, attracted iron filings, and gave magnetic 
powers to needles ; nor did any agitation of the mercury or mie- 
tal within, either in consequence of mechanical motion or heat, 
alter or suspend their polarity. 
III. Imperfect conducting fluids do not give polarity to steel 
when electricity is passed through them; but electricity passed 
through air produces this effect. Reasoning on this phenome- 
non, and on the extreme mobility of the particles cf air, J con- 
cluded, as M. Arago had likewise done from other considerations, 
that the Voltaic current in air would be affected by the magnet. 
I failed in my first trial, which I have referred to in a note to 
my former paper, and in other trials made since, by using too 
weak a magnet; but I have lately had complete success ; and 
the experiment exhibits a very striking phenomenon. 
Mr. Pepys having had the goodness to charge the great bat- 
tery of the London Institution, consisting of two thousand double 
plates of zinc and copper, with a mixture of 1168 parts of water, 
108 parts of nitrous acid, and 25 parts of sulphuric acid, the 
poles were connected by charcoal, so as to make an are, or co- 
lumn of electrical light, varying in length from one to four inches, 
according to the state of rarefaction of the atmosphere in which 
it was produced; and a powerful magnet being presented to 
this are or column, having its pole at a very acute angle to it, 
the are, or column, was attracted or repelled with a rotatory 
motion, or made to revolve, by placing the poles in different 
positions, according to the same law as the electrified cylinders 
of platinum described in my last paper, being repelled when the 
negative pole was on the right hand by the north pole of the 
magnet, and attracted by the south pole, and vice versa. 
It was proved by several experiments that the motion depended 
entirely upon the magnetism, and not upon the electrical induc- 
tive power of the magnet; for masses of soft iron, or of other 
metals, produced no effect. 
The electrical are or column of flame was more easily affected 
by the magnet, and its motion was more rapid when it passed 
through dense than through rarefied air; and in this case, the 
conducting medium or chain of aériform particles was much 
shorter. 
I tried 
