Mr Barlow's Electro-Magnetic Experiments. 379 
small moveable piece is suspended, is then so much depressed, 
that the proposed revolving wire slopes at an angle of about 40° 
with the horizon. In this state the circuit of the battery is com- 
pleted through the mercury in the basin and the other conduct- 
ing wire, when immediately the short wire commences a rotation, 
as it would do about the south end of a magnet, but in a pro- 
portionally less degree, as the directive power of the earth is Jess 
than that of a magnet of the kind here supposed. 
“ This similarity of action naturally leads us to infer a similar 
cause, and that this cause is no other than the terrestrial mag- 
netism; still, however, in order to render this conclusion the 
more indisputable, Mr Faraday changed the inclination of the 
wire, making it first equal to the angle of the dip; and when, 
under these circumstances, the wire was placed so as to coin- 
cide with the dip itself ; viz. when placed in the magnetic meri- 
dian, sloping from sputh to north, there was no motion; and 
when the angle was still farther increased, so as to exceed the 
angle of the dip, it was projected in two different directions, ac- 
cording as it was made to slope to the north or to the south, 
which is precisely what ought to be the case, on the supposition 
of the motion being caused by the magnetism of the earth. 
“ For let o z 9 o s', in (Fig. 13, and 14.), represent the freely 
suspended wire in the plane of the meridian, sloping respective- 
ly to the north and south: and let NS in both figures denote 
the direction of the terrestrial magnetism, then it is obvious in 
the first of these figures, that whether the slope be towards the 
north or towards the south, it will be always on the same side 
of the line NS, and will, in both cases, be projected in the same 
direction, with respect to the observer, situated as forming a part 
of the galvanic circuit, and consequently in opposite directions, 
as referred to the circular rotation of the extremity z or z\ But 
when the slope is less than the dip, then the wire, in its two 
positions, being found on opposite sides of the line of direction, 
and passing still to the same hand of an observer situated in the 
wire, a rotation will ensue similar to those that have been de- 
scribed in Experiment I. 
