TERRESTRIAL MAGNETO-ELECTRIC INDUCTION. 
173 
against such effects. Considering the universality of the magnetic influence 
of the earth, it is a consequence which appears very extraordinary to the mind, 
that scarcely any piece of metal can be moved in contact with others, either 
at rest, or in motion with different velocities or in other directions, without an 
electric current existing within them. It is probable that amongst arrange- 
ments of steam-engines and metal machinery, some curious accidental mag- 
neto-electric combinations may be found, producing effects which have never 
been observed, or, if noticed, have never as yet been understood. 
181. Upon considering the effects of terrestrial magneto-electric induction 
which have been described, it is almost impossible to resist the impression 
that similar effects, but infinitely greater in force, may be produced by the 
action of the magnet of the globe upon its own mass, in consequence of its 
diurnal rotation. It would seem that if a bar of metal be laid in these lati- 
tudes on the surface of the earth parallel to the magnetic meridian, a current 
of electricity tends to pass through it from south to north, in consequence of 
the travelling of the bar from west to east (172.), by the rotation of the earth; 
that if another bar in the same direction be connected with the first by wires, 
it cannot discharge the current of the first, because it has an equal tendency 
to have a current in the same direction induced within itself : but that if the 
latter be carried from east to west, which is equivalent to a diminution of the 
motion communicated to it from the earth (172.), then the electric current 
from south to north is rendered evident in the first bar, in consequence of its 
discharge, at the same time, by means of the second. 
182. Upon the supposition that the rotation of the earth tended, by magneto- 
electric induction, to cause currents in its own mass, these would, according to 
the law (114.) and the experiments, be, upon the surface at least, from the parts 
in the neighbourhood of or towards the plane of the equator, in opposite 
directions to the poles; and if collectors could be applied at the equator and at 
the poles of the globe, as has been done with the revolving copper plate (150.), 
and also with magnets (220.), then negative electricity would be collected at 
the equator, and positive electricity at both poles (222.). But without the con- 
ductors, or something equivalent to them, it is evident these currents could 
not exist, as they could not be discharged. 
183. I did not think it impossible that some natural difference might occur 
