Gravity must
be caused by an agent acting constantly according to certain laws;
but whether this agent be material or immaterial, I have left to the
consideration of my readers.'[1]
Faraday does not see the same difficulty in his contiguous particles.
And yet, by transferring the conception from masses to particles,
we simply lessen size and distance, but we do not alter the quality
of the conception. Whatever difficulty the mind experiences in
conceiving of action at sensible distances, besets it also when it
attempts to conceive of action at insensible distances. Still the
investigation of the point whether electric and magnetic effects
were wrought out through the intervention of contiguous particles or
not, had a physical interest altogether apart from the metaphysical
difficulty. Faraday grapples with the subject experimentally.
By simple intuition he sees that action at a distance must be exerted
in straight lines. Gravity, he knows, will not turn a corner, but
exerts its pull along a right line; hence his aim and effort to
ascertain whether electric action ever takes place in curved lines.
This once proved, it would follow that the action is carried on by
means of a medium surrounding the electrified bodies. His experiments
in 1837 reduced, in his opinion, this point of demonstration.
He then found that he could electrify, by induction, an insulated
sphere placed completely in the shadow of a body which screened it
from direct action.
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