380 Mr Barlow’s Electro-Magnetic Experiments. 
Exp. XI. “ To exhibit the action of two galvanic wires on each 
other. 
** The apparatus which I employed for this purpose is shown 
in (Fig. 15.), where AB represents a rectangular board, and D, 
E, two upright pieces of wood, carrying each a cross piece at top 
with several holes for receiving the cups mmf, n n', which, by 
this means, may be placed at different distances ; a little mercu- 
ry is poured into each of these, so as to communicate with the 
wires inserted through the side of the cup, and terminate with 
fine points. The wires w a a' w\ w b V w’ are bent, as shown in 
the figure, and have small holes drilled at a, 5, 6', whereby 
they may be hung freely upon the points of the wires m, &c. 
and carrying small weights w, w', &c. in order to bring the points 
of suspension to correspond as nearly as possible with the centre 
of gravity, whereby the wires are moved by the least force. The 
conducting wires from the extremities of the battery Z and C 
are terminated as represented in the figure, and being each 
brought to the respective cups, so that z z' are respectively in- 
serted in the cups m w, and d c into the cups m' n r , the circuit 
will be made through the two wires a a ', b b\ in the same direc- 
tion ; and these being free to move about the points in the re- 
spective cups, will be strongly attracted towards each other, even 
at the distance of several inches. 
“ Let now the branch z of the conducting wire Z z be length- 
ened, so that it may pass round the board, and be inserted in 
the cup n ', while z' is inserted in the cup m as before ; lengthen 
also the branch c of the conducting wire C c, passing it round 
the board, and dipping it into the cup % while d is immersed in 
m' as at first ; by this means, the circuit passes from z to c along 
the wire b h\ and from z' to d along the wire a a ' ,* in short, the 
circuits in the two wires are now made in opposite directions, 
and the wires experience and exhibit a mutual repulsion. Hence 
we learn, that two galvanic wires, parallel to each other, and in 
which the circuit is made in the same direction, are attracted to- 
wards each other ; but they are mutually repelled when the cir- 
cuit passes in- opposite directions, a result first deduced by M. 
Ampere, and which he has made the foundation of his theory of 
electro-magnetism, by assuming, that the powers exhibited by 
