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the operation of the natural laws we have endeavoured to explain 
in the previous paper — Deity being the sustainer of these laws 
and of the active energies of nature. 
We know that the mind of man deals with and directs free 
power or force, when it sends it to the muscles for the purposes of 
voluntary motion ; and we are therefore justified by parity of reason 
in holding that, when free force comes in upon the mind from the 
outer world, through the vibratory movements above referred to, 
the mind will be susceptible to its influence. This is not only a 
consistent, but a necessary conclusion. 
It is, be it observed, not substance, but power, which the vibrat- 
ing molecules bring to the mind, and which the mind receives. We 
may hold also that the force or power thus received or appropriated 
by the mind, and the physical movements which accompany it, take 
end in the brain, being there neutralised by the control which we 
know the mind to exert over physical power. 
It is common, we admit, for physicists to explain the perception 
of light and sound as due to the vibratory movements of the physi- 
cal molecules which impinge on the retina and auditory nerve. But 
in doing so they give us merely the outer manifestation, and 
neglect the unseen essence and efficacy. For it is the force which 
causes the movement, and not the movement which causes the 
force. It is force which causes the cannon ball to fly with its 
destructive violence. Take away the force, and the iron lies harm- 
less on the ground. 
Without the iron, indeed, or other atomic body, we could neither 
obtain nor use physical force for physical purposes, and for these 
reasons — first, though we can take force from one body and pass 
it to another, we can never obtain it freed from its physical con- 
nection. The second reason that physical substance is necessary 
for physical purposes is this — Though the iron is passive, and the 
sport of its Master — Force, and though it is force that carries it 
through the air, still the iron evidently performs an important part 
in physical dynamics. It is because iron and other atomic bodies 
are impenetrable by each other, that when the cannon ball meets 
the iron target, one or other of them must yield. The question is 
not, which of them is the hardest — for a piece of tallow, we know, 
may be fired through a deal board — the question is — whether the 
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