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orange and violet, were mutually substituted! Yet, when new terms are used, as when we read a treatise on colours, in a foreign language, we follow the author without difficulty. Nor is it only to the reader, that this mode of innovation is productive of confusion. The author himself, however strongly he may have connected the new idea with the sign, is still under the influence of prior habits; and will thus less readily discover an error in his reasoning, when the propositions are just, in the former signification of the terms. It is this ambiguity, which has deceived Dr. Darwin, in classing the phenomena of mind.
Pleasure, and pain, are considered in Zoonomia, in two points of view, eitheir simply as phenomena, or as the causes of phenomena. It is only in the latter sense, to pleasure, or pain, when causing fibrous motions, that Dr. Darwin gives the name of sensation; and the reader is earnestly entreated by him to keep the distinction in his mind, p. 12. All those sensorial motions, therefore, which do not terminate in exciting the muscles, or organs of sense, are excluded from his system, as they are not irritations, sensations, volitions, nor associations; and among these the greater number of our pleasures and pains must be classed: yet, in many passages of Zoonomia, the original limitation of the term seems to have been forgotten, and sensation to have been used, as synonymous with pleasure, and pain.'
Mr. Brown next points out several phænomena of life, which cannot be reduced to any of Dr. Darwin's four classes of sensorial motions; and he traces, in a very striking manner, the want of precision in the Zoonomia, arising from the adaptation of new definitions to common words.
In the third Section, (p. 70,) the author considers the Classes of Fibrous Motions; following the arrangement of the Zoonomia. Dr. D. has supposed that all fibrous contractions were originally caused by the irritations of external objects: but that painful or pleasurable sensations often accompanying those irritations, the contractions became exciteable by those sensations; and that, as efforts of the will accompanied those sensations, the contractions were at length, by habit, causable by volition alone.
To this doctrine, Mr. Brown objects that, whatever may be attributed to the power of habit, it is impossible that the reversed babit, here supposed, should produce the effects ascribed to it; that a person, for example, should repeat the alphabet backward, with ease, because he cannot repeat it in the usual order. He adds that, even according to Dr. Darwin's own statement, the cause of fibrous contractions must be uniformly resolved into irritation.
In the fourth Section, of Stimulus and Exertion, the author displays great ingenuity, in combating Dr. D.'s opinion that sensorial power is expended on every sensorial change:
That we have no reason to consider the spirit of animation, as expended during exertion, will be evident, if we attend to the nature
of exertion. Irritation, sensation, volition, and association, are no sensorial power: they are only its modes, or qualities. When a fibre is contracted, sensorial power is not communicated to the fibre, but simply motion, which is a necessary consequence of a certain state of sensorial power. The motion, indeed, perishes; but the motion is a state of the fibre, the effect of a state of sensorial power, and of that state only for sensorial power existed in the organ, without affecting it, previously to the application of the stimulus. When the contraction of the fibre has ceased, we are entitled to infer, that the cause of the contraction has ceased; but we are not entitled to infer more. The cause of contraction was not the simple existence of sensorial power, but its existence, in a certain state; and we may, therefore, justly infer, that it has returned to the state, in which it existed, before the action of the stimulus.
If, by the expenditure of sensorial power, nothing more be meant, than a slight change of its place in the system, this may be admitted, without adding much strength to Dr. Darwin's theory. Thus, when the vessels of the brain are stimulated by the blood, the spirit of animation may be allowed to quit the fibres, which it caused to contract; but no reason can be adduced, to prove, that it is wholly lost, which will not equally prove, that the quantity, secreted by the brain, quits the sensorium, immediately after secretion, instead of being distributed to the different fibres of the system. When sensation is propagated along a nerve, the sensorial power, in the centre of the nerve, is expended; but it ceases not to exist, and we have no reason to suppose, that the membrane of the nerve suddenly becomes permeable to sensorial power, and suffers it to escape from the system. If, therefore, the general quantity of the spirit of animation be not diminished by exertion, and if, at the same time, a continual supply of that fluid be secreted, the fibrous motions must continually increase in violence; and those phenomena, which seem to proceed from deficiency of strength, are thus wholly inexplicable, on the principles of the sensorial theory.
The ingenious author of that theory himself considers exertion, as, in some instances, attended with an increase, rather than a diminution, of sensorial power. This, he observes, "sometimes happens from the exhibition of opium and of wine," Vol. II. p. 363; and, "when the vessels of the skin are exposed to great heat, an excess of sensorial power is produced in them, which is derived thither by the increase of stimulus above what is natural," Vol. II. p. 321. No reason can be shewn, that the application of heat to the skin should be attended with an increase of sensorial power, which will not prove, that this increase should be the effect of every stimulus. In that case, no bounds can be fixed. The spirit of animation, whether exerted, or at rest, is accumulated in the organs; and violent inflammation, or palsy, must, according to Dr. Darwin, be, in a few hours, the inevitable consequence of life.'
Mr. Brown afterward proceeds to shew the difficulties, on the principles of the Zoonomia, attending the supposition that the expenditure of sensorial power is proportioned to the degree
of the stimulus applied. According to his usual process, he then proves that, even conceding these points to the author, the doctrine will not account for the phænomena of animal life. As this subject forms so important a part of the Zoonomia, we shall extract his principal remarks:
If inaction induce an accumulation of sensorial power, the most indolent should be the most capable of labour, and exercise be, in consequence, hurtful, as it diminishes the general quantity of the spirit of animation. If it be said that the secretion in the brain is proportionally increased, by the greater quantity of oxygene, inspired during exercise, the impossibility of fatigue, in these circumstances, will be a sufficient answer. If the secretion be precisely equal to the expenditure, the fibres will continue, in the same state, as before exertion, and, if it be greater, the secretion will continue, in an increasing ration; so that the fibres will be excited to unnatural action by their accustomed stimuli. But the quantity secreted is not equal to that expended; for fatigue is the invariable consequence of violent exercise. No benefit, therefore, will be derived to the system; but, on the contrary, general debility must ensue for the spirit of animation, in the brain, being less, will secrete a less supply. The circulation being slower, less oxygene will be combined with the blood, and the vital functions be thus, more and more, impeded, by the increasing reaction of direct, and indirect debility.
If it be said, that, though violent exercise may induce weakness, it, notwithstanding, when used with moderation, invigorates the system, the truth of the observation will be admitted; but Dr. Darwin's theory must, at the same time, be abandoned, Let us suppose the exercise to continue, during a certain number of hours. The spirit of animation, it is conceived, though diminished, at the end of that period, is not diminished, at the end of the first hour. If it be merely equal to the original quantity, the exercise may be indefinitely continued, without producing strength, or weakness; and, if it be greater, the causes of accumulation increasing, the sensorial power will be much more abundant, when the hours have elapsed; or, in other words, the fibres will not be fatigued.
The indolent, and sedentary, instead of being subject to nervous fevers, should, on this hypothesis, be subject to continual attacks of inflammatory fever: for, during their inactivity, the spirit of animation must be accumulated, in so great a degree, as to render the slightest irritation insupportable.'
On the subject of Sensual Motions, the author has combated the account given in Zoonomia of the immediate organs of sense; and we find, in this section, a command of language and a variation of style, which evince that Mr. Brown has not always confined himself within the thorny maze of metaphysics:
No subject is so interesting to our curiosity, as the nature of those feelings, which connect us with the world, and in which our
happiness, or misery, consists; nor is there any, in which we have derived less aid from the wisdom of past ages. The consciousness of thought is implied in the consciousness of existence; yet we are still as unacquainted with the mode, in which this mental change is carried on, as we were, before the first philosophic savage had wondered at himself. The phantasms, and species, and ideas, of the ancient schools no longer delude us with the belief of knowledge; and all, we have learned, has served only to add to the difficulty of unlearning error. What is this subtile feeling, we have still to ask, so variable, yet ever present; which clevates us to the rank of gods, or degrades us below the dull insensibility of the earth, on which we tread? The bubble still floats before our eyes, gay with all the variety of light; but what delicate touch shall retain it in expansion, and arrest its fleeting colours? The author of the Botanic Garden, who so happily succeeded, in "enlisting imagination under the banner of science,' a design, easy only to powers like his, is not content, to have enlarged our acquaintance with the objects around us. Undeterred by the failure of his predecessors, he has attempted
"The doubtful task,
The immediate organs of sense, according to the theory proposed, are not expansions of their peculiar nervous medulla, but are composed of fibres, intermixed with sensorial power. They are stimulated to contraction, like the muscular fibres, from which they differ, in possessing a greater proportional quantity of the vital spirit. The motions of these fibres constitute our ideas; and, when an organ is destroyed, the ideas of that organ necessarily perish.
Can we then suppose, that Milton described the beauties of his ideal paradise, without any conception of what he described; or, that unconscious of any loss, he could mourn, with so much apparent feeling, his insensibility of
"Day, or the sweet approach of ev❜n, or morn,
could the fox of Homer, to use the words of Dr. Darwinthe long shadow of the flying javelin-have been elegantly designed, "to give us an idea of its velocity, and not of its length," when the poet himself was incapable of the idea. We might, with as much reason, expect, that the rude materials of a building, ignorantly thrown together, should rise into a model of perfect architecture. If the lively descriptions of visual objects, which delight, and astonish us, in the poems of Homer, and Milton, have been produced by the total absence of ideas, who will not abjure the useless pomp of knowledge ? "Where ignorance is bliss, 'Tis folly to be wise."
• * Pleasures of Imagination, Book I. 1. 45.'
Mr. Brown observes, that Dr. D. has differed from other metaphysicians in his definition of an idea, in confining his defi nition to one part of the process; the motion of certain fibres : for all admit that a certain change of the organ precedes the change of the mind. Yet Dr. Darwin, deceived, as in other cases, by its former signification, uses the term idea also to express a state of the spirit of animation. For the arguments by which the author proves the distinction between our ideas and fibrous motions, we must refer to the work. In the course of them, Mr. Brown has introduced a defence of the Berkeleyan doctrine of general ideas; in which we are surprised to observe no indications of an acquaintance with Mr. Horne Tooke's opinions concerning general terms.
The dissimilarity between ideas and fibrous motions is farther illustrated, in the section on the production of ideas:
• When the idea of a cup is in the sensorium, a similar concave must exist, in the organ of touch. The sensorial power must be absent, within the circumference of the idea; so that, though the surface be pierced, no sensation should ensue. Yet, even when a larger concave is the subject of our thought, as a cave, or a valley, a slight puncture is sufficient to recall our attention to the objects
To the idea of a concave surface nothing more is necessary, than the existence of a similar retrocession of the spirit of animation, in the sensorium. But, as that fluid cannot rise above the surface of the skin, a convexity of sensorial power can be formed, only by the general, or partial retrocession of the sensorial power around it. In the former case, the whole of the remaining surface of the body must be insensible in the latter, the idea of the convex surface cannot exist, without the idea of another ascending surface, and of an intermediate concavity.
The ideas, which Dr. Darwin ascribes to touch, instead of approaching to infinity, are limited by his theory to a small class. Though every nerve of the system be, at the same moment, compressed, and though each compression be perceived, our ideas of figure must be bounded by the extent of the spirit of animation. We may, indeed," inspect a mite;" but we cannot "comprehend the heaven." We may view, as a whole, the humbler plant; but a tree will tower above the most expanded sensorium. The dwarf may look down on others, more diminutive than himself; but, though the age of giants were to return, they would not appear to him larger, than the two-feet dimensions of his own mind.
When a body is pressed violently against the organ of touch, so as to excite a large concavity, pain ensues, and the effect should be similar in imagination; yet we do not feel pain, when we think of a mountain, or a valley.
Even if the theory advanced were free from other chjections, the point, which it takes for granted, remains to be proved; that the compressed organ resembles the compressing body. The reverse will be