inquires Dr. Brown, "which we can discover in the mere sensation of fragrance, that is itself significant of solidity, extension, or whatever we may regard as essential to the existence of things without? As a mere change in the form of our being, it may suggest to us the necessity of some cause or antecedent of the change. But it is far from implying the necessity of a corporeal cause;—any more than such a direct corporeal cause is implied in any other modification of our being, intellectual or moral—in our belief, for example, of the most abstract truth, at which we may have arrived by a slow development of proposition after proposition in a process of internal reflective analysis, or in the most refined and sublime of our emotions, when, without thinking of any one of the objects around, we have been meditating on the divinity who formed them—himself the purest of spiritual existences. Our belief of a system of external things, then, does not, as far as we can judge from the nature of the feelings, arise from our sensations of smell, more than from any of our internal pleasures or pains." (Brown's Philosophy of the Human Mind. Lecture XX.)

Odorous particles, then, have never been submitted to Dr. Brown's only test of materiality, and yet he, and all other immaterialists, without any hesitation, pronounce them to be matter. The spirit, like these particles of odour, can exist in connexion with the body or separate from it; and yet it forms no part of the fleshy tabernacle. If like the particles of odour, it really eludes the grasp of the muscular organs, and if neither these odoriferous particles, nor the spirit, can be proved by any muscular effort to have solidity and extension; why, then, should one be called material, and the other immaterial?

If the mind be unextended, how can it receive any sensations from things without? It could not act upon bodily organs, for they are extended. Neither could bodily organs act upon it.

Philosophers have endeavoured to invent numberless hypothesis to account for the action of matter on the mind, which they have assumed to be immaterial. The old Peripatetic doctrine of perception, by species or phantasms, which for so many centuries held so unlimited a sway in the philosophic world, was probably originated to connect material with immaterial substances. When this absurdity slowly died away, other hypothesis, no less erroneous, immediately supplied its place. Des Cartes, seeing no possibility of any reciprocal action between matter and something that was inextended, invented his system of occasional causes, and represented the external world entirely incapable of affecting the mind in any way whatever. He ascribed all the sensations and affections of the mind to the immediate agency of the Deity, virtually rendering external objects entirely useless to the mind. This conjecture has been modified by succeeding philosophers without, however, removing its absurdities. It is useless to revert to all the absurd theories which have from time to time distracted the metaphysical world, and which have been originated for no other purpose than to uphold the still greater absurdity of immaterialism. Philosophers of ancient times imagined the existence of an immaterial substance, unextended in its nature, like nothing. To support this wild and vague imagination, learned metaphysicians have given birth to innumerable conjectures, in order to connect this imaginary substance with the material world.

Dr. Brown, however, being a little more wise than the immaterialists who preceded him, does not attempt to connect the mutual affections, existing between matter and mind, by substituting some conjectural intervening causes. Instead of this, he advocates the direct affection of the mind by the presence of material objects—that the change of state in the one is produced by the change of state in the other, independently of intervening causes. Now this, in our view, is really what happens.

We believe that matter can only act upon mind because mind is an extended material substance. But Dr. Brown supposes there is no absurdity in matter acting upon that which is unextended. He endeavours to substantiate the possibility of the direct mutual affections of mind and matter, by referring to some examples of matter acting upon matter as in gravitation. (Brown's Philosophy of the Human Mind. Lecture XXX.) But we do not conceive these cases to be in the least analogous; for there is no absurdity in supposing one extended substance to act upon another which is also extended. But for extended substances with parts to act upon unextended substances is without a parallel, and inconceivably absurd. Indeed there could be no action at all; an immaterial mind could not act upon an immaterial mind any more than nothing could act upon nothing. To talk about matter affecting that which is inextended and without parts, is to talk about matter affecting nothing.

The very fact of the external organs affecting the mind without any intervening cause, the same as other matter affects other matter, is an argument of the strongest kind in favour of the materiality of mind. A piece of iron is affected in a certain manner by introducing into its presence a loadstone, so the mind is affected in a certain manner by the presence of light upon the retina, or by the presence or odour upon the olfactory nerve. If, then, mind can be directly affected by other substances, the same as matter directly affects matter, why should it be called an immaterial substance?

If resistance to our muscular efforts, as Dr. Brown supposes, be our only test of solidity and extension, and consequently of matter, then mind itself has the greatest claims to materiality. A muscular effort is nothing more than an effort of the mind. Without the mind the muscles are incapable of any effort whatsoever. Two men stretch out their arms, press their hands together, and resist each other with great force. In this example as it is commonly said, the muscular efforts of the one are resisted by the muscular efforts of the other; but as the muscles have no power of themselves, the facts of the case are, that the mind of the one truly resists the mind of the other through the medium of their respective muscles. If that which causes resistance then be material, mind must be material.

If two bodies of iron of equal size were moving with equal velocities towards each other, upon meeting they would destroy each others motion, and the next moment, though in contact, there would be no signs of resistance; not so with the resistance which mind offers to mind through the medium of the muscular organs; the resistance can be continued at the option of the two resisting minds; hence mind exhibits resistance in a greater degree than other substances, and should, therefore, according to Dr. Brown's test, be considered material in preference to all other substances.

No two atoms of spirit or any other matter can occupy two or more places at the same time. We have never known of a circumstance of the spirit of man residing in the body and out of it at the same time. No particles of light, odour, heat, electricity, can occupy two places at once. These substances can only be extensively diffused by being extensive in quantity. The particles of light which enter the right eye are not the same which enter the left eye. Though their qualities may be exactly alike, yet they are separate individual substance, as much so as if they were millions of miles asunder. The same is true of the atoms of spirit and all other substances.