To this corpuscular view, however, though it is unquestionably the sort of view to which, in our ultimate physical inquiries into the phenomena of matter, we must come, you may, perhaps, not be sufficiently accustomed, to enter fully into the reasoning on the subject. It will probably be less difficult for you, if we take rather, as an illustration, the simpler case of impulse; in which the bodies affecting each other are not, as in chemistry, indistinguishable corpuscles, but masses, clearly defined, and easily perceptible.
I need not, of course, repeat the arguments formerly stated, to prove that attraction, however general it may be as a law of matter at all visible distances, does not continue, but gives place to an opposite tendency at those smaller distances, which we are unable to perceive with our weak organs, and which we learn to estimate only by effects that are inconsistent with absolute contact;—for example, by the well-known fact of the compressibility of bodies, which could not take place if their particles were already in contact, and which by continually increasing resistance to the compressing force that would bring the corpuscles nearer, shews, that there is, at different degrees of nearness, a tendency continuing to operate, which is the very reverse of attraction. There is, therefore, every reason to believe,—since repulsion, as the fact of forcible compression shews, takes place while the particles of bodies are still at a certain distance,—that the motion produced in one body by another, and ascribed to immediate impulse, is produced, without actual contact, by this mutual repulsion, as it is called, of the bodies when brought within a certain invisible degree of vicinity to each other; or, in other words,—for repulsion means nothing more mysterious than this simple fact,—the tendency which bodies, in certain relative positions of apparent but not actual contact, have to fly off from each other with certain degrees of velocity, as in certain other relative positions, of distinguishable distance, they have a tendency to approach each other. This repulsion, or tendency from each other at one point of nearness, is of itself as easy to be conceived, as that attraction, or tendency toward each other at other points of distance, to which we give the name of gravitation; and it is only from our greater familiarity with the one, as operating at distances which are visible, while the other,—except in a few cases, such as those of magnetism and electricity,—operates only at distances which are imperceptible to us, that we feel a little more difficulty in admitting the repulsion than the attraction of matter. There is then,—however universal gravitation may seem, when we think only of perceptible distances,—a certain point of near approach, before actual contact, at which gravitation ceases; and, beyond this point, the tendency of bodies toward each other is converted,—as the force necessary to compress them evidently shews,—into a tendency from each other; both tendencies, indeed, being inexplicable, but the one in no respect more so than the other.
For this apparent digression, on a point of general physics, I make no apology, as it is absolutely necessary for illustrating the particular case to which I am to proceed. The consideration of it requires, what the whole of this discussion, indeed, has already required from you, no small exercise of patient attention; but I trust that I sufficiently prepared you for this, in a former Lecture, when I stated the importance of such attention, not merely in relation to the subject considered at the time, but as a part of your mental discipline, and the advantage which might thus be derived to your intellectual character, from the very difficulties which the subject presents. It is in philosophy, as in many a fairy tale. The different obstacles which the hero encounters, are not progressively greater and greater; but his most difficult achievements are often at the very commencement of his career. He begins, perhaps, with attacking the castle of some enchanter, and has to force his way, unassisted, through the griffins and dragons that oppose his entrance. He finishes the adventure, with the death of the magician—and strips him of some ring, or other talisman, which renders his subsequent adventures comparatively easy and secure. I cannot venture to say, indeed, that a perfect acquaintance with the difficulties of the present question, and of some of the late questions which have engaged us, will be such a talisman to you, in your future career of intellectual science. But I may safely say, that the habit of attentive thought, which the consideration of subjects, so abstract, necessarily produces, in those who are not too indolent to give attention to them, or too indifferent to feel interest in them, is more truly valuable than any talisman, of which accident or force might deprive you. The magic with which this endows you, is not attached to a ring, or a gem, or any thing external; it lives, and lives forever, in the very essence of your minds.
When a billiard ball, on being struck, approaches another, which is at rest, it soon arrives at the point of seeming, but not actual contact, at which their mutual attraction ceases, and the force which it has acquired still carrying it on, it passes this bounding point, and arrives at a point at which repulsion has already begun. Accordingly the body, formerly at rest, now flies off, on a principle precisely similar, (though the mere direction be opposite) to that by which the same ball, if dropped from a hand that supported it, would, without the actual impulse of any body, have quitted its state of rest, as in the present case, and have gravitated, or, which is the same thing, have moved of itself toward the earth.
Before the first ball, which you will, perhaps more easily remember by the name, A, arrived so very near to the second ball B, as to have come within the sphere of their mutual repulsion, this second ball was at rest, that is to say, it had no tendency to move in any direction. This state of rest, however, is only one of the many states, in which a body may exist; and if, which must surely be allowed, a body having a tendency to continued motion, be in a different state, from one which has no such tendency, this change of state implying, it must be remarked, not even the slightest loss of identity, has been produced in the body B, by the mere vicinity of the body A. For the sake of illustration, let us now suppose this body A to be hot or luminous. It will still, as before, produce the new state of tendency to motion, in B, when it arrives within the limits of their sphere of repulsion. Is it less conceivable, then, that the mere presence of this hot or luminous body should produce the new sensation of warmth, or of colour, which are different states of the sentient mind, without affecting in the slightest degree the identity of the mind itself, than that it should produce, without any loss of absolute identity, in the body B, an immediate tendency, in that body, to move along with a certain velocity, a state as different from that in which it remains at rest, as the sensation of warmth, which is one state of the mind, is different from the sensation of colour, which is another state of the mind? Nor does the parallel end here; for, since a body at rest, acquiring a tendency to begin motion in one particular direction, as, for example, to move north, must be in a different state from that in which it would have been, if it had acquired an instant tendency to move east, or in any other direction; and, the direction once begun, being the same, since a body having a tendency to move with one velocity, must, at every moment of its progress, be in a different state from that in which it has a tendency to move with a different velocity, it is evident, that the mere presence of a body may produce, in a second body, according to the difference of their positions and relative magnitudes, a variety of states, that, when all the varieties of direction, and all the varieties of velocity are estimated together, may be considered as infinite,—equal at least in number, to the different states of which the mind is susceptible, in its almost infinite variety of feelings; and all this without any essential change, that can affect the identity of the quiescent or moving body, or any essential change, that can affect the identity of the mind.
I am aware, that, when you consider, for the first time, this assertion of an infinite variety of states, corresponding with all the innumerable varieties of direction and velocity, in the tendencies of a simple billiard-ball, which, in the various circumstances supposed, appears to us precisely the same, in all its sensible qualities, you may be apt to conceive, that the assertion must be founded on a mistake, and, from the influence of former prejudice may be inclined to think, that, when it exhibits a tendency to begin to move east, at one time, and, at another time, a beginning tendency to move north, this does not arise from any difference of state in itself, but from its being merely carried along by the first ball, which was itself previously moving in one or other of these particular lines of direction. When the elastic billiard-ball, however, bounds away from the ball which strikes it, this supposition is manifestly inapplicable;—and, in all cases, it is the influence only of former prejudice which can lead you to this opinion,—the influence of that prejudice, by which you may have been accustomed to consider impulse, not as inducing a tendency to motion at some little distance, but as involving the necessity of actual contact. To destroy this prejudice, a very little reflection on the phenomena of elastic bodies, in their shocks and mutual retrocessions, is surely all that can be requisite; and if the motion of B, and consequently its tendency to motion, have begun, without contact of A, as it afterwards continues while A, the elastic body which struck it, is moving back in an opposite direction, it could not be by mechanical trusion, as carried along by A, which is still at some points of distance from it when its motion begins, and at still greater distance the longer the motion continues, that B has assumed any one of its variety of states,—that, for example, in which, in one case, it tends to move east, in another case to move north, in one case to move rapidly, in another slowly. To say that the body acquires this new tendency because it is impelled, is only to say that it is impelled because it is impelled. It is an equally idle use of language, to affirm, as if a word could obviate the difficulty instead of merely stating it,—that A, in communicating a different tendency to B, which was before at rest, does this by a principle, or power of repulsion; for this, as I have said, is merely to state in a single word, the regularity in certain circumstances of the very fact asserted. The different tendencies of B, and consequently the different states in which B exists,—are not the less different, in whatever manner the difference may have been produced, or by whatever word, or combination of words, the difference may be expressed. There is no magic, in the phrase, principle of repulsion, or power of repulsion, which can render the same, states or tendencies that are in themselves opposite;—for, as far as we understand the phrase, it expresses nothing more than the invariableness of the simple fact, that in certain circumstances of relative position, bodies have a tendency to fly off from each other, as in certain other circumstances of relative position, which constitute the phenomena of gravitation, they have a tendency to approach. Whatever term we may employ to denote it, it is still a physical fact, that at a certain point of near and seemingly close approach of another mass, a body which was before in a state of rest, acquires immediately a tendency to fly off in different directions, and with different velocities at different times, and consequently, that, if the tendency to begin or to continue motion, in one direction, and with one velocity, be a state different from that which constitutes the tendency to begin or to continue motion in another direction, and with another velocity, the ball B, in these different circumstances, however identical it may be in substance, exists in two different states;—or all states, however different, may be said to be the same.
It may be admitted, then, that the feeling of rapture is a state of mind, completely different from that which constitutes the feeling of agony,—that the sensation of the fragrance of a rose, has no resemblance to our conception of a sphere or of an equilateral triangle,—and that, in general, all those thoughts and emotions, which,—more truly than the mere union of the immortal spirit within us with the body which it animates,—may be said to constitute life,
“Love, Hope, and Joy, fair Pleasure's smiling train,—
Hate, Fear, and Grief, the family of Pain;”
these, as they prevail, in different hours, render the same individual mind more unlike to itself, if its states or tendencies alone, and not its substantial identity be considered, than the minds perhaps of any two human beings, at the same moment. But still, as we have seen, even from the analogy of the material world,—which was supposed to furnish a powerful objection, it is no argument against the absolute identity of the mind, that exists in different states, however opposite, any more, than it is an argument against the absolute identity of a body, that it, at one moment, has a tendency to one particular motion,—at another moment a tendency to a different motion,—and at another moment, no tendency whatever to motion of any kind; since, in all these cases, as much as in the varying affections of the mind, there is a change of state, with absolute identity of substance.