874 Mr Barlow's Electro-Magnetic Experiments. 
the north end of the magnet upwards, the motion is from left to 
right, and the contrary with the magnet reversed. This expe- 
riment is due to M. Ampere. 
“ A very pleasing addition has been made to this apparatus 
by Mr J. Marsh. It consists in having a second point descend- 
ing from F, which is made to rest in an agate cup, fixed on the 
top of the magnet, Fig. 6., and upon which the whole machine 
is balanced, having a perfect freedom pf motion ; and to pre- 
serve this balance, the magnet is placed vertically in a foot. The 
machine being now charged with acid, a compound motion takes 
place, the zinc cylinder revolving in one direction, and the cop- 
per vessel in another, producing thus a very pleasing effect ; 
the latter, however, is by no means so rapid as the other, in con- 
sequence of the weight of the acid, and in fact that of the whole 
machine being supported on the lower point” 
Exp. V. u To show the effect of a horse-shoe magnet on a freely 
suspended galvanic wire . 
“ Let Z z, Fig. 7., denote a part of the galvanic wire, freely 
suspended by the chain connection at o, proceeding from the 
zinc end of a battery, its lower extremity being amalgamated 
and slightly immersed in a reservoir of pure mercury, having a 
connection at C with the other extremity of the battery. NS is 
a horse-shoe magnet, placed as shewn in the figure. 
u The contact being now made at C and Z, the hanging part 
of the wire o z will be thrown out of the mercury into the posi- 
tion o z' ; the contact being thus broken, it falls by its own gra- 
vity into the mercury, by which means, the contact being re- 
newed, it is again projected, and so on with an extraordinary ra- 
pidity ; and if the position of the magnet be reversed, or the 
contact be changed, the direction of the motion will be changed 
also, but the effect will be the same. 
M This singular motion may be still explained by the hypo- 
thesis that has been advanced ; for the wire having a tendency 
to pass round the north end of the magnet to the right hand, 
and round the south end to the left hand, is urged by equal 
forces directly in a line with the open space of the magnet, the 
equality of the two forces preventing the rotatory motion about 
