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that it was made in the circuit of metal round the cylinder, 
and that my object was to find the relative motion of the 
cylinder and the electricity. Altogether I think it may be 
taken as experimental proof of the fact previously stated 
that if a steel top were spinning under the inductive 
influence of a body charged with negative electricity the 
effect would be that of a current round the top such as 
would render it magnetic. 
The cause of terrestrial magnetism has not been the 
subject of so much speculation as many much less important 
phenomena. It seems to have been regarded as part of the 
original nature of things like gravity, and the heat of the 
sun, as a cause from which other phenomena might result, 
but not as itself the result of other causes. 
Yet, when we come to think of it, it has none of the 
characteristics of a fundamental fact ; it appears intimately 
connected with other things, and when two phenomena 
have a relation to each other, there is good reason for 
believing them to be connected, either as parent and child, 
or else as brother and sister, the one to be derived from the 
other, or else them both to spring from the same cause. 
Now the direction of the earth’s magnetism bears a 
marked relation to the earth’s figure, and yet it can have 
had no hand in giving the earth its shape, which is fully 
explained as the result of other causes ; therefore, we must 
assume that the figure of the earth has something to do 
with its magnetism, or what is more likely, that the rota- 
tion which causes the earth to keep its shape, also causes it 
to be magnetic. 
If this is the case then there must be some influence at 
work with which we are as yet unacquainted — some cause 
which coupled with the rotation of the earth, results in 
magnetism. From the influence which the sun exerts on 
this magnetism we are at once led to associate it with the 
cause. Yet the cause itself cannot be the result of either 
