That Hartley's system, as far as it differs from that of Aristotle, is neither tenable in theory, nor founded in facts.
Of Hartley's hypothetical vibrations in his hypothetical oscillating ether of the nerves, which is the first and most obvious distinction between his system and that of Aristotle, I shall say little. This, with all other similar attempts to render that an object of the sight which has no relation to sight, has been already sufficiently exposed by the younger Reimarus, Maasz, and others, as outraging the very axioms of mechanics in a scheme, the merit of which consists in its being mechanical. Whether any other philosophy be possible, but the mechanical; and again, whether the mechanical system can have any claim to be called philosophy; are questions for another place. It is, however, certain, that as long as we deny the former, and affirm the latter, we must bewilder ourselves, whenever we would pierce into the adyta of causation; and all that laborious conjecture can do, is to fill up the gaps of fancy. Under that despotism of the eye (the emancipation from which Pythagoras by his numeral, and Plato by his musical, symbols, and both by geometric discipline, aimed at, as the first propaideuma of the mind)—under this strong sensuous influence, we are restless because invisible things are not the objects of vision; and metaphysical systems, for the most part, become popular, not for their truth, but in proportion as they attribute to causes a susceptibility of being seen, if only our visual organs were sufficiently powerful.
From a hundred possible confutations let one suffice. According to this system the idea or vibration a from the external object A becomes associable with the idea or vibration m from the external object M, because the oscillation a propagated itself so as to re-produce the oscillation m. But the original impression from M was essentially different from the impression A: unless therefore different causes may produce the same effect, the vibration a could never produce the vibration m: and this therefore could never be the means, by which a and m are associated. To understand this, the attentive reader need only be reminded, that the ideas are themselves, in Hartley's system, nothing more than their appropriate configurative vibrations. It is a mere delusion of the fancy to conceive the pre-existence of the ideas, in any chain of association, as so many differently coloured billiard-balls in contact, so that when an object, the billiard-stick, strikes the first or white ball, the same motion propagates itself through the red, green, blue and black, and sets the whole in motion. No! we must suppose the very same force, which constitutes the white ball, to constitute the red or black; or the idea of a circle to constitute the idea of a triangle; which is impossible.
But it may be said, that by the sensations from the objects A and M, the nerves have acquired a disposition to the vibrations a and m, and therefore a need only be repeated in order to re-produce m. Now we will grant, for a moment, the possibility of such a disposition in a material nerve, which yet seems scarcely less absurd than to say, that a weather-cock had acquired a habit of turning to the east, from the wind having been so long in that quarter: for if it be replied, that we must take in the circumstance of life, what then becomes of the mechanical philosophy? And what is the nerve, but the flint which the wag placed in the pot as the first ingredient of his stone broth, requiring only salt, turnips, and mutton, for the remainder! But if we waive this, and pre-suppose the actual existence of such a disposition; two cases are possible. Either, every idea has its own nerve and correspondent oscillation, or this is not the case. If the latter be the truth, we should gain nothing by these dispositions; for then, every nerve having several dispositions, when the motion of any other nerve is propagated into it, there will be no ground or cause present, why exactly the oscillation m should arise, rather than any other to which it was equally pre-disposed. But if we take the former, and let every idea have a nerve of its own, then every nerve must be capable of propagating its motion into many other nerves; and again, there is no reason assignable, why the vibration m should arise, rather than any other ad libitum.
It is fashionable to smile at Hartley's vibrations and vibratiuncles; and his work has been re-edited by Priestley, with the omission of the material hypothesis. But Hartley was too great a man, too coherent a thinker, for this to have been done, either consistently or to any wise purpose. For all other parts of his system, as far as they are peculiar to that system, once removed from their mechanical basis, not only lose their main support, but the very motive which led to their adoption. Thus the principle of contemporaneity, which Aristotle had made the common condition of all the laws of association, Hartley was constrained to represent as being itself the sole law. For to what law can the action of material atoms be subject, but that of proximity in place? And to what law can their motions be subjected but that of time? Again, from this results inevitably, that the will, the reason, the judgment, and the understanding, instead of being the determining causes of association, must needs be represented as its creatures, and among its mechanical effects. Conceive, for instance, a broad stream, winding through a mountainous country with an indefinite number of currents, varying and running into each other according as the gusts chance to blow from the opening of the mountains. The temporary union of several currents in one, so as to form the main current of the moment, would present an accurate image of Hartley's theory of the will.
Had this been really the case, the consequence would have been, that our whole life would be divided between the despotism of outward impressions, and that of senseless and passive memory. Take his law in its highest abstraction and most philosophical form, namely, that every partial representation recalls the total representation of which it was a part; and the law becomes nugatory, were it only for its universality. In practice it would indeed be mere lawlessness. Consider, how immense must be the sphere of a total impression from the top of St. Paul's church; and how rapid and continuous the series of such total impressions. If, therefore, we suppose the absence of all interference of the will, reason, and judgment, one or other of two consequences must result. Either the ideas, or reliques of such impression, will exactly imitate the order of the impression itself, which would be absolute delirium: or any one part of that impression might recall any other part, and—(as from the law of continuity, there must exist in every total impression, some one or more parts, which are components of some other following total impression, and so on ad infinitum)—any part of any impression might recall any part of any other, without a cause present to determine what it should be. For to bring in the will, or reason, as causes of their own cause, that is, as at once causes and effects, can satisfy those only who, in their pretended evidences of a God, having first demanded organization, as the sole cause and ground of intellect, will then coolly demand the pre-existence of intellect, as the cause and ground-work of organization. There is in truth but one state to which this theory applies at all, namely, that of complete light-headedness; and even to this it applies but partially, because the will and reason are perhaps never wholly suspended.
A case of this kind occurred in a Roman Catholic town in Germany a year or two before my arrival at Goettingen, and had not then ceased to be a frequent subject of conversation. A young woman of four or five and twenty, who could neither read, nor write, was seized with a nervous fever; during which, according to the asseverations of all the priests and monks of the neighbourhood, she became possessed, and, as it appeared, by a very learned devil. She continued incessantly talking Latin, Greek, and Hebrew, in very pompous tones and with most distinct enunciation. This possession was rendered more probable by the known fact that she was or had been a heretic. Voltaire humorously advises the devil to decline all acquaintance with medical men; and it would have been more to his reputation, if he had taken this advice in the present instance. The case had attracted the particular attention of a young physician, and by his statement many eminent physiologists and psychologists visited the town, and cross-examined the case on the spot. Sheets full of her ravings were taken down from her own mouth, and were found to consist of sentences, coherent and intelligible each for itself, but with little or no connection with each other. Of the Hebrew, a small portion only could be traced to the Bible; the remainder seemed to be in the Rabbinical dialect. All trick or conspiracy was out of the question. Not only had the young woman ever been a harmless, simple creature; but she was evidently labouring under a nervous fever. In the town, in which she had been resident for many years as a servant in different families, no solution presented itself. The young physician, however, determined to trace her past life step by step; for the patient herself was incapable of returning a rational answer. He at length succeeded in discovering the place, where her parents had lived: travelled thither, found them dead, but an uncle surviving; and from him learned, that the patient had been charitably taken by an old Protestant pastor at nine years old, and had remained with him some years, even till the old man's death. Of this pastor the uncle knew nothing, but that he was a very good man. With great difficulty, and after much search, our young medical philosopher discovered a niece of the pastor's, who had lived with him as his house-keeper, and had inherited his effects. She remembered the girl; related, that her venerable uncle had been too indulgent, and could not bear to hear the girl scolded; that she was willing to have kept her, but that, after her patron's death, the girl herself refused to stay. Anxious inquiries were then, of course, made concerning the pastor's habits; and the solution of the phenomenon was soon obtained. For it appeared, that it had been the old man's custom, for years, to walk up and down a passage of his house into which the kitchen door opened, and to read to himself with a loud voice, out of his favourite books. A considerable number of these were still in the niece's possession. She added, that he was a very learned man and a great Hebraist. Among the books were found a collection of Rabbinical writings, together with several of the Greek and Latin Fathers; and the physician succeeded in identifying so many passages with those taken down at the young woman's bedside, that no doubt could remain in any rational mind concerning the true origin of the impressions made on her nervous system.
This authenticated case furnishes both proof and instance, that reliques of sensation may exist for an indefinite time in a latent state, in the very same order in which they were originally impressed; and as we cannot rationally suppose the feverish state of the brain to act in any other way than as a stimulus, this fact (and it would not be difficult to adduce several of the same kind) contributes to make it even probable, that all thoughts are in themselves imperishable; and, that if the intelligent faculty should be rendered more comprehensive, it would require only a different and apportioned organization,—the body celestial instead of the body terrestrial,—to bring before every human soul the collective experience of its whole past existence. And this, this, perchance, is the dread book of judgment, in the mysterious hieroglyphics of which every idle word is recorded! Yea, in the very nature of a living spirit, it may be more possible that heaven and earth should pass away, than that a single act, a single thought, should be loosened or lost from that living chain of causes, with all the links of which, conscious or unconscious, the free-will, our only absolute Self, is coextensive and co-present. But not now dare I longer discourse of this, waiting for a loftier mood, and a nobler subject, warned from within and from without, that it is profanation to speak of these "mysteries tois maede phantasteisin, os kalon to taes dikaiosynaes kai sophrosynaes prosopon, kai oute hesperos oute eoos outo kala. To gar horon pros to horomenon syngenes kai homoion poiaesamenon dei epiballein tae thea, ou gar an popote eiden ophthalmos haelion, haelioeidaes mae gegenaemenos oude to kalon an idae psychae, mae kagae genomenae—to those to whose imagination it has never been presented, how beautiful is the countenance of justice and wisdom; and that neither the morning nor the evening star are so fair. For in order to direct the view aright, it behoves that the beholder should have made himself congenerous and similar to the object beheld. Never could the eye have beheld the sun, had not its own essence been soliform," (i.e. pre-configured to light by a similarity of essence with that of light) "neither can a soul not beautiful attain to an intuition of beauty."