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woven by the imperfect brains of men. Were I to venture on a criticism of 
Professor Kirk’s paper, it would be as to his division of all substances 
(using that term in its metaphysical sense) into mind and matter. In this 
division, though with great diffidence, I should be disposed to differ from 
him. I believe there are other verities or existences in God’s universe 
besides mind and matter. I believe forces of various kinds have a real exist- 
ence ; that many of these can neither be resolved into mind (meaning by 
that term an intelligent substance) nor matter. All that we know of force 
and matter, so far as mathematical demonstration is concerned, lies in a very 
narrow compass. For all the purposes of mathematics and of demonstrable 
natural philosophy, a very simple definition of force and matter suffices. 
Whatever moves or can be moved is matter, and whatever can cause matter 
to move is force ; but when we quit the domains of pure mathematical 
demonstration, we soon become involved in purely metaphysical difficulties, 
those difficulties which are leading, as I believe, such philosophers as Pro- 
fessor Tyndall and Mr. Grove astray. The tendency of natural philosophers 
who quit the region of pure mathematical demonstration is to confound force 
and matter as things which are identical instead of being distinct from each 
other. This has ever been the course of the metaphysical rather than the physical 
reasoner. The purely physical reasoner has a distinct conception of force and 
matter as two very different existences which cannot be confounded together. 
The metaphysical reasoner who would pass beyond the rough practical dis- 
tinction of force and matter which satisfies all the problems of the physicist 
is involved at once in metaphysical difficulties. The essence of matter 
evades all his researches ; he meets everywhere the evidence of force ; and the 
effect of force alone is all that his senses convey to his intelligence. He, 
therefore, as Boscovich did, resolves all matter into what he calls centres of 
force, and so, quite as effectually as Berkeley, the pure metaphysician 
banishes all matter from nature. Hence, therefore, metaphysical researches 
would effectually banish all matter from existence, and land us in a universe 
of pure force, or what I presume Professor Kirk would denominate pure 
mind. But do not such metaphysical considerations as these banish, not 
only the inductions of common sense, but all the real knowledge we have 
acquired? I cannot prove the existence of matter metaphysically any more 
than I can prove the existence of mind. There is, however, a practical way 
of resolving these metaphysical subtleties. If I doubt the existence of 
matter, I have only to run my head against a wall to get a demonstration 
that will at once rudely banish any scepticism induced by metaphysical 
arguments. We have, I believe, as good evidence for the existence of 
matter as we have for the existence of force ; and as good evidence that force 
and matter are distinct entities as we have for the existence of either. 
When we enquire, however, whether force is inseparable from matter ; 
whether all matter is not endowed with force and whether there are not 
forces completely separated from, and not co-existent with, matter, we come 
upon most debateable subjects far removed from the bounds of strict 
logical demonstration. If by mind we are to understand an intelligent 
