318 Mr Barlow's Electro-Magnetic Experiments. 
lion, will be projected towards the extremity AB of the board, 
and if the contact be changed, by making the zinc connection at 
C and the copper at Z, the wire will be driven towards the 
other extremity. As no magnet is introduced in this experi- 
ment, we have a right to attribute the motion to the effect of 
the terrestrial magnetism, the direction of it corresponding pre- 
cisely with what we ought to expect from such action. For the 
terrestrial magnetism of our latitude being of the same kind as 
that exhibited by the southern pole of a magnet, the moveable 
wire ought to pass from right to left in the first case, and from 
left to right in the second, to an observer situated as forming 
a part of the galvanic circuit ; that is to say, with the first con- 
tact the wire ought to be projected towards AB, and with the 
second towards DG-. 
“ To prove that the motion proceeds from this cause, let the 
south pole of a strong magnet be brought under the board be- 
tween Z and C, and make the contact again ; and the same 
motion will take place, but in a much stronger degree, the wire 
being now thrown very forcibly out of the mercury. 
The effect therefore being precisely of the same character, 
but much more powerful in the latter case than in the former, 
we have a right to conclude that the cause of the motion in both 
cases is of a like nature, the one proceeding from a southern 
polarity artificially produced, and the other from the natural 
magnetic action of the terrestrial sphere, as stated by Mr Fara- 
day, to whom we are indebted for this interesting experiment. 
F&cp. X. “ To produce a rotation of the galvanic wire by means 
of the terrestrial magnetism . 
45 This is also an experiment due to Mr Faraday, and which 
provtks, in the most satisfactory manner, the influence of the ter- 
restrial 1 magnetism in the production of a rotatory motion. It 
is performed as follows: a very light copper, or platina wire, 
about 6 inches long, is suspended very freely from a larger wire 
proceeding from either end of the battery, by means of the chain 
connection described in several of the preceding experiments, 
and at its lower extremity a small piece of cork is attached, in 
order to keep the wire buoyant on a basin of pure mercury, 
about 1 0 inches in diameter. The wire by which the above 
