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SOME THOUGHTS (PHILOSOPHICAL) ON VISION. That the sense of vision is the noblest which the Deity has imparted to humanity, bas been uniformly acknowledged by philosophers; not only the sages of antiquity, but pbilosophers of all ages, have admitted its high precedency in the sum of human enjoyments. Newton, who turned the energies of his great mind to an investigation of the phenomena which produce to the mind the delightful impressions of color; Berkeley, who struck out a new theory of vision, in which he explains its laws upon immutable principles ; Adam Smith, who philosophically viewed the influence of sight upon our scientific attainments, in the history of the pro. gress of astronomy; Dr. Reid, who, although he acknowledges most of the leading positions maintained by certain philosophers who preceded him in these matters, evinced his usual determination to quarrel with them all, because they did not investigate on his alleged principles of common sense; Burke, who systematically unfolded the impressions which outward objects produce upon the mind through the medium of optics; and, lastly, Professor Dugald Stewart, and Dr. Chalmers, have, amongst numerous others, investigated its proper objects, and recognized the vast pre-eminency of this single sense, over all others.

So much of genius and learning, indeed, has been expended in endeavouring to explain the principles, or the laws, by which the science of optics is governed, that I may almost incur the charge of presumption, in touching on the subject. However, there are some points connected in various ways “ with this most delightful of all our senses," as Addison ternis it, which may justify a few further observations, from a plain thinker. The ingenious Ray has well remarked, “ as the eyes are the windows, to -let in the species of all exterior objects into the dark cells of the brain, for the information of the soul; so are they flaming torches, to reveal to those abroad how the soul is moved and affected."

By far the greater part of the ideas we derive from perfection and sensation, are, indeed, let into the mind, through the faculty of vision. Through its aid, we not only " inspect a mite," and roam over the boundless scene of terrestrial nature, as she stands displayed in all her forms of complex and beautiful variety; but “ comprehend the heavens," and marshal the radiant host, which canopy the firmament. Calculations upon the distance, magnitude, and motion of the celestial bodies, could never, it is manifest, bave entered the human mind, had this sense, alone, in the economy of our own frame, been denied us.

From vision, alone, we become acquainted with the minute and unknown worlds wbich the microscope unfolds; realms peopled with a universe of animated existence, which must, otherwise, for ever bave eluded man's knowledge.

The fascinating scenes which, in some countries, spread a charm of ineffable beauty over whatever has relation to vision ; the picturesque and radiant hues which the scenery of Greece unfolds; the rich and glowing colors which diversify the atmosphere, and the skies of Italy, associated and connected as they are with the finer intellectual enjoyments of their respective inhabitants, could never have entered into the poet's imagination, or fired bis enthusiasm, had we never enjoyed the faculty of vision.

The laws of perspective, as they amalgamate, so to speak, in the alembic of the eye ; the blended colors of the pictorial art, which administer in so high a degree to the formation of our tastes and the tone of our moral feelings, would cease to operate, were mankind deprived of the images which crowd into the sensorium from every part of the arena of visible nature. The principles and the laws by which the faculty of vision is regulated, have frequently, and perhaps sufficiently, been explained by those who have studied optics as a science. The refrangibility and reflexibility of light, for instance, and its effects; the action of homogeneous and heterogeneous rays; the angles of incidence, of reflection, of refraction, and of deviation ; with the varied phenomena produced upon the optic sense, from the contraction and dilation of the pupil of the eye, through the medium of the particles of light, which strike reciprocally upon that, and all bodies within its influence : all these, with numerous others, ascertained through subordinate details in the theory of sight, have been scientifically unfolded by philosophic observers. But these may be termed, minor points, which grow out of a close study of the phenomena, developed in the economy of sight; the grand innovation, however, which the Bishop of Cloyne wrought in this science, when he taught mankind, that they never saw the distance, respectively, between objects; but that our knowledge of their relative proximity or remoteness, and consequently, that an idea of their magnitudes was acquired purely through our judgment, aided by a course of experience, is of a far higher character. The appearance of Berkeley's Treatise, it is well known, reformed the theory of optical science, and established other laws, by which the economy of vision was explained. He instructed man, that though it is the noblest of our sensual faculties, vision was yet fallacious, inasmuch as it is from experience we ascertain the true position of objects within the reach of our sight, and whilst he established his hypothesis upon an immutable basis, these new positions, opposed as they were to certain prejudices and habits contracted by mankind, were quickly instrumental in exploding many hallucinations, fatally destructive of truth and accuracy. His postulates upon these subjects, although, they had, like the positions of Galileo and Copernicus, when they taught that the earth moved, to struggle with the preconceived notions of the generality of mankind, were quickly espoused by the discerning part of it.

Amongst others, this new theory was recognized as legitimate, and becomingly lauded by the celebrated Dr. Reid. Severe sarcasm, and loud and bitter irony, are deservedly employed in ridicule of the bishop's hypotheses, connected with the non-existence of matter: but when, on the other hand, he struck out a new track for the reformation of the laws of vision, the doctor yielded him just praise for the penetrating research, and cautious vigilance, which are manifested throughout his enquiries.

At the present day, although paradox still abounds, the pretensions of the Bishop of Cloyne, in his famous postulates concerning matter, are altogether lost sight of. A disciple of his school, indeed, (if such there be,) would at present be deemed an absolute madman; nor can we in this age give implicit credence to Dr. Reid, when he dogmatically asserts, through the whole of his famous Metaphysical Treatise on the Principles of Common Sense, that Berkeley, and after him Hume, proved most logically their chimerical notions, from the well-known hypotheses of Locke, concerning what he terms, “ Secondary qualities in bodies.”

We will hear the professor himself:---" What Locke had proved," says he, (Sect. 6, “ Of Seeing,")" with regard to the sensations we have by smell, taste, and hearing, Bishop Berkeley proved, no less unanswerably, with regard to our other sensations; to wit, that none of them can in the least resemble the qualities of a lifeless and insentient being, such as matter is conceived to be. Mr. Hume,” he adds,“ has confirmed this by his authority and reasoning.---This opinion surely looks

with a very malign aspect upon the old hypothesis ; yet that hypothesis has been retained and conjoined with it. And what a breed of monsters,” ejaculates our professor of moral philosophy, " has this produced !" And he afterwards adds, as a commentary, “ Surely no age ever produced such a system of opinions, justly deduced with great acuteness, perspicuity, and elegance, from a principle universally received."

Now, in this and many other passages throughout bis “Enquiry,the author of “ Common Sense” notoriety in these studies, classes Locke, Des Cartes, Malebranche, and their commentators, Berkeley and Hume, all together, and of course, par consequence, makes the first responsible for the inconceivable absurdities of the two last. As the subject is connected with vision, we shall venture a caveat against this opinion, not only broadly insinuated, but openly avowed.

Great names should, in common justice, be cleared from unmerited obloquy; and though, in this practical age, it may be said, that it is not so much the names of the mighty dead, as the progress of science, and the improvement of our contemporaries, which ought to form the end and aim of an essayist; yet when the two-fold object may be attained of illustrating a writer's real meaning, and removing the errors of a contemporary, or a past school of metaphysics, we may be justified in the attempt.

Locke first assumed, it is well known, that every object exposed to our sight is painted on the retina of the eye, which communicates an idea of the object to the brain, and which idea is thus at once shot into the sensoriuni ; which hypothesis, in substance, embraces that of Berkeley, by anticipating his doctrine of all objects being at an equal distance from the sense. This, however, by no means meets with approbation from Dr. Reid and his followers, who allege, though somewhat vainly, that the notion of perceiving all the objects of animate and inanimate nature, by a representation or image, termed an IDEA, (an epithet which, how much soever they ridicule it, is in frequent and even necessary use among themselves,) is a fallacy, and leads the way to errors of dangerous magnitude. But, notwithstanding all the vapouring of the “ Common Sense" school, it has long been manifest to mankind, that the phenomena connected with vision cannot be explained without adopting this hypothesis of Locke's, which, in effect, is the same as that adopted and improved by Berkeley.

In the instance of the celebrated operation performed by Cheselden, namely, the couching a youth of fourteen years of age, who never recollected having the faculty of sight. The lad thought, for a considerable time after obtaining his sight, that all objects were painted on his eye. It is further recorded of this youth", that his friends, who thonght be knew what pictures represented, afterwards found that they were mistaken, for it appears that about two months after he was couched, he discovered, for the first time, that they represented solid bodies, when before that time he considered them merely as partly colored plains, or surfaces, Jiversified with variety of paint; but it further appears that even then he was no less surprised, expecting the pictures would feel like the things they represented, and was amazed when he found those parts which by their light and shadow appeared round and uneven, felt fiat, Jike the rest. He asked which was the lying sense, feeling or seeing ?

These are authenticated facts, and no theory; but they are (if need

* By the master of the Free-school in Haxley, Lincolnshire, who has preserved a few details concerning him.---Dated 1731.

be) abundantly corroborated from other testimony. Ju the fine arts, how, indeed, it might be asked, unless objects were delineated upon the eye, could pictorial exhibitions represent nature in all her varieties and proportions ? Perspective, with all its ramified laws---the minute and exquisite shadings, with their innumerable gradations, so blended and amalgamated, as clearly and distinctly to represent distance, must for ever fail in producing correct transcripts of their archetype---nature, if, in truth, the scenes of this last did not present to the eye as level a surface as canvas or marble. A landscape of Claude, or one of the finest efforts of imagination from the pencil of Salvator Rosa, could not otherwise, it is plain, affect the mind of the beholder with similar emotions to those which they receive from real scenes of nature.

But Dr. Reid, in his capacity of general reformer in matters of metaphysical authority, has bestowed his usual sarcasms upon another doctrine of Locke, connected with vision-his doctrine of colors. Here also he confounds the author of the “ Essay on Human Understanding," with those who have foisted false corollaries and absurdity on his wellknown theory concerning the non-existence of colors. It is, however, worthy of remark, that while Dr. Reid labors to prove that Locke was an enthusiast in these matters, who led men's minds astray from the truth, he often, in substance, himself admits the philosophical propriety of bis positions. For though he (Dr. Reid) asserts, that it is a dangerous and fatal error to teach that color has no real existence in bodies themselves ; yet woald the doctor, or any of his disciples, have been puzzled to advance the shadow of argument in proof of its being essentially any thing separate from body; any thing, in fact, more than Locke pronounces it to be. “What!” says a disciple of the “Common Sense" school, in the true spirit of their founder, “has the great Newton employed his powers in investigating the properties of colors, and shall another philosopher deny their very existence ?It is very easy to misrepresent an author's meaning, and then descant upon the apparent absurdities of his dogmas. The principle which Locke advocated, was simply this :---After enumerating what he, not improperly, terms the Primary Qualities, which inhere in all bodies in the universe, (with which every reader of the writings of this great man is sufficiently conversant) he ranks their color, which affects the eye with agreeable or unpleasing sensations, under the head of Secondary Qualities. These last, as is also sufficiently known, Locke considers only as a sort of power to produce certain affections, or, as he terms them, ideas, upon our senses, " which, says he,“ have been generally looked upon as real qualities inhering in the things so affecting us.” This he attempts to prove by a variety of arguments ; but as we have undertaken to illustrate this point, we will avail ourselves of an argument or two of our own. If those peculiar shadings, (in all their hues and tints) which we call color, and which adhere to the surface of most bodies of nature, are in truth not powers, what are they !--- Is this color a substance, or is it immaterial !---Will any one assert, that this color is a thing, having distinct qualities from the body, to the surface of which it adheres, and which it often diversifies with such brilliant shades !--- In questions of this kind, we must always separate, in our ideas, the thing which strikes the eye with the peculiar sensation which men denominate color, and its substratum, which is separate and distinct from it. If not substantial or material, this thing which strikes upon the eye must be immaterial, and consequently invisible. But if color, which variegates with such unnum. bered tints the visible creation, be, in point of fact, only an effect produced by the rays of light, striking on the surface of a body, then it is beyond all question, non-existent when not perceived. It is assuredly very conceivable, that this effect (of color) may be produced by the subtle and insensible parts of the superficies of a body, when so disposed as to reflect the rays of light in a different manner from another body, whose minute or insensible parts are disposed after another manner. These minute or insensible parts, pre-dispose the rays of the sun, so to reflect upon the surface of this body, as to create in the mind of the spectator, a sensation of blue, green, red, yellow, black, and their infinite intermediate varieties. Color, therefore, (or our ideas of color, for it is the same thing,) is entirely dependant upon the peculiar, insensible modification of the surface of the body, pre-disposed and arranged for the action of light. The peculiar affection of the optical sense, moreover, which we call color, is not only an idea in the mind of the beholder, as the disciples of the “ Common Sense” school allege that Locke asserts, but is dependant solely upon the texture of the minute parts of the surface of a body. If this be true, and that it is, we need only appeal to reason, whence comes all the clamor of Dr. Reid and his followers, who assert that Locke was among the most eminent of those who had misled mankind in these matters? Mr. Locke shall, finally, speak for himself. “Colors, therefore,” says he, "are, in truth, powers, which (through the instrumentality of light,) operate upon the primary qualities of the bodies, that is, the bulk, figure, texture, or motion of their insensible parts, so as in a peculiar manner to act on our senses, and produce in us the ideas of color in their varieties."

From these simple positions, with regard to vision and its laws, it is alleged the “ brood of monsters" (in Dr. Reid's language) bas sprung. But we have shewn that, so far is the Lockeian hypothesis concerning color, as it affects the eye, from foisting on mankind any dangerous error, that, through it, many phenomena connected with this branch of physiology are rendered more intelligible, If it be still maintained, conformably with the opinion of “ Common Sense" philosophy, that the prelate we have already noticed, deduced his famous conclusions respecting the material world logically from Locke's postulates, we reply, that he clearly did no such thing. He grounds the whole fabric of his reasoning upon a petitio principii, assuming that the great Arbiter of nature has given us senses for the sole purpose of misleading our judgments, and making us the perpetual sport of unreal phantoms; a conceit which is as preposterously absurd in a moral sense, as his negation of matter was in a physical. If, therefore, the author of the Berkeleyan theories did not legitimately deduce his doctrines from the assumptions of Locke, the reader will immediately agree, that it is difficult to imagine, that he could himself have credited the singular paradox which he chose for the display of his logical and rhetorical abilities. When we view a fine landscape, comprehending a beautiful assemblage of rural and domestic objects ; when the eye wanders amid the wild desolation which marks the mountain scenery of Savoy, Mount Blanc rearing its summit in awful grandeur in the distance ; and whilst contemplating the wide and boundless ocean in storms, we feel within us a conviction, that the Deity could never have designed our senses to have been panders to deception, or vehicles of delusive dreams. We read of a philosopher who refuted the absurd dogma of a person who questioned the reality of motion, by walking before him ; and of another who proved the existence of matter, by striking his hand violently against a hard substance. Might we not almost conclude, that a writer who knew how to marshal the objects of the natural world in evidence so well as Berkeley has done in his second dialogue between Hylas and Philonous, (p. 251) in which every corollary furnishes an argument in refutation of his favorite postulates, could never

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