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a very different thing to show,, as must be done ere it is philo- 
sophically accepted, that it is a legitimate inference from 
fact. If any one is habituated exclusively to the contem- 
plation of motions which he regards as “ forces,” in an 
incessant and protracted watching of these “ forces " in their 
action, they may so occupy his thought, as to seem to him 
the only realities in the universe. The magnetic affection of 
a piece of iron, for example, called the magnetic force in that 
iron, may be exclusively thought of, till it seems to the ex- 
clusive thinker a substance as real as the iron. It is but a 
changeful mode of the iron's existence, which might pass away, 
and the substance be all there as before; but it ceases to 
be so in the exclusive thinker's state of mind, and becomes 
itself an entity — in fact becomes a thing while it is only 
a movement ! The abstract idea of force, like the abstract 
idea of everything else, is nothing but a state of the thinking 
mind at the time when such an idea is entertained, and the 
idea of the force of any actual substance is only that of a state 
or mode in which that substance exists at the time when it 
has that force; but when anyone has given himself up to 
exclusive thought of the mere manner of a thing's existence, 
it soon becomes, as we have said, a thing itself to him. But 
we are not concerned so much here with the way in which the 
idea is formed, as with the legitimacy of the idea considered as 
an inference from the facts of nature. 
There is what we think a very clear distinction which is of 
great importance in such investigations as that which we are 
now pursuing. It is that between force and motion. If we 
take such a machine, for instance, as that of Mr. Wyld, by 
means of which the French authorities, as well as our own, 
are endeavouring to furnish the light-houses along’ our coasts 
with the electric light, we have a good illustration of this 
distinction. This machine, when on a small scale, is driven by 
the hand — when on a larger scale, it is driven by a steam 
engine. By the turning of a crank a system of toothed 
wheels and pinions is set in motion — the motion of these is 
communicated to a part of the machine which revolves with 
great rapidity near the poles of a series of powerful magnets, 
collecting the magnetic currents from them. The ordinary 
motion is thus allied to the magnetic motion, which is changed, 
into an electric motion, and concentrated in the poles of the 
machine itself. The result is a stream of electric motion which 
is almost incredibly powerful. When that stream is changed 
again into that peculiar movement which we call light , it is 
so strong as to make itself visible on the surface of the ocean 
at three or four times the distance at which the best lamps with 
