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relation,” to pass into another. By the operation of these 
three varieties of force, each acting in its own particular way 
on atoms of matter, and under the conceivable varieties in 
the relation of place, we shall have a great diversity of causes, 
though we repudiate all other alleged forces implicated in 
magnetism, chemistry, physiology, and light, of the separate 
identity of which we have no positive evidence, and as it 
seems to me no need. 
The forces of gravitation, electricity, and caloric, or heat, 
are each so common that we may consider them to be 
acting in concert in insensible spaces intervening between the 
atoms in masses of matter. What their several actions are 
is not of moment in the present state of our argument ; it 
cannot be doubted that each action is peculiar to the force 
to which it belongs, nor that the consequence of each at any 
time varies with the relation of place. In the interstitial 
spaces the action of each force will be distributed probably 
among many reactions, reducing effects to greater minute- 
ness, while increasing them in number, to operate as causes in 
the next ensuing stage of the physical operation. 
I would point here to an instructive metaphor, illustrating 
the production of physical events by the reciprocal rela- 
tions of causes and effects, to be found in the formation of 
language. Consonants may be likened to the atoms to be 
related at any particular time ; vowels to the forces which 
relate them ; and the varied sounds of each vowel to the 
forces under the different relations of place. Consonants 
with a certain modification of vowel-sound, make up a definite 
syllable ; so atoms, combined by certain forces and relations, 
constitute a certain material thing. And just as two syllables 
will not result from the same orthography and orthoepy, so a 
sameness of physical cause, or in other words, sameness of 
force with sameness of place, cannot produce two facts. 
We thus arrive at sufficient knowledge of the fundamental 
principles of physical nature to perceive a distinction between 
Cause and Force which seems to have been lost sight of. We 
have been putting one for the other by philosophizing as 
though force governed by laws irrespective of the relation 
of place, were the same thing as Cause having the relation of 
yplace involved in its constitution. We have made the mistake 
of supposing that all which is true of cause, remains true 
when we substitute for it its two elements, force and time, 
omitting its important element, place. The laws of force, 
like all the other truths of Nature, are invariable ; not so the 
action of force between cause and effect, which we know by 
observation is determined by their relative positions, often 
