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concentrating the rays with precision to form the image on the posterior surface; and would probably have the effect of a simple lens placed before the eye, throwing upon the latter convergent rays, and presenting objects erect, but less and less distinct as they are further from the focus. But whether this be a correct explanation or not, there is another account of vision, which this writer seems never to have met with, and which, while it affords a ready solution of the phenomena of the erect images seen by the writer before us, seems to us at once more simple, clear and satisfactory, than the suggestions of the memoir we are exam-ining.
Dr. Hutton mentions a tract, published in 1813, by a clergyman of the name of Horn, on “the Seat of Vision"-of which he thus speaks—“ In this little piece, after a neat and concise account of the different hypotheses and arguments of his predecessors in this line, the author relates some ingenious experiments, accompanied with reflections on the subject, and finally deduces a theory which appears more rational and satisfactory than any of the former.” This tract we have never had the good fortune to meet with, but we regard the following extract quoted by Dr. Hutton, as very ingenious and pleasing, if not demonstrably true :
* The reader must have anticipated, and therefore will now readily comprehend the manner in which I conceive vision to be accom. plished. Rays, from all points of such objects as are opposed to the organ, pass through the pupil, and, after refraction in the different humors, delineate perfect but inverted pictures, on the retina at the bot. tom of the eye; these pictures are instantly reflected, in their various colors and shades, on the anterior portion of the concavity ; another reflection from hence raises images of the external objects near the middle of the vitreous humor, in their natural order and position; these images make due impressions on the opposite base of the nerve, which are transmitted by it to the brain, thus the sensation is produced, and vision performed."
If these suggestions be correct, several modifications must be made in the doctrines we have stated as those most approved on the subject of vision; and while such modifications might be requisite, no unauthorized ridicule can be ventured towards these doctrines. These modifications, indeed, suggested as they are in Mr. Horn's ingenious tract, coincide in a remarkable degree with some of the facts described by our anonymous writer.
The latter says—** No particular part of the eye-ball can be regarded as the seat of vision. It is with this organ as with the others, one part of the apparatus is intimately connected with the rest"
and though “ the optic nerve
is certainly the main-spring of the whole apparatus of vision,” yet " when the whole eye is sound, then every part moves simultaneously at one impulse, and conveys an image, for so we must speak to the sensorium.”
** Mr. Horn, in 1813, had written, “ Neither the retina nor the choroides, is the immediate seat of vision, but the optic nerve being restored to that dignified function in the theory, which it naturally possesses in the organ, all the inferior instruments will be found harmoniously co-operating with it, in producing the various phenomena of vision.
Notwithstanding the remarkable agreement between some of the points of these two statements, there is that in the latter, which renders it abundantly more satisfactory to us than the former. We mean that it gives a precise account, how an erect image is formed, and then refers to the harmonious action of the apparatus and nerve, for conveying that image to the brain ; while the other merely rests on the vague assertion, that * all the parts moving simultaneously convey an image to the sensorium," a declaration which is subsequently repeated in this form : “ It is on the central ganglion that the image is first ormed, it is there that it is first perceived."
This declaration actually contains the substance of the writer's theory of vision, and of what are offered as "discoveries in the mental faculties;" for the writer goes on to say, “ it is there that the spectra or images remain, when we see them after our eyes are closed. It is from this precise spot that they are conjured up, as it were, when the mind has a desire to recall them."
Now, as to the way in which these fancied images are produced and illuminated on the central ganglion, the writer had of course to devise something, and, in truth, has succeeded in making up a very remarkable hypothesis. “I do not contend," says our author, “that the particles of light themselves, as luminous particles, reach the internal organs of vision, and illuminate the spectra there, or produce spectra there.”. But, “ whatever power sets light free in the first instance, is still in force when internal spectra are to be illuminated; and although light in its free or perceptible state, which is luminousness, cannot be transmitted through the nerve, yet the very motion that it gives to the nerve may set light free again internally. This same power
can set light free in the form of lightning, a mass of light which shall rend the highest mountains,” (a sufficiently novel feat for light to perform ;) and it can set free a quantity just sufficient to illuminate that
something—that nameless something in the brain—which gives intimation of the presence of external objects; and by the same means it can re-illumine the same spot, so that the images of things external can be brought again to our mental sight.” We will not hold up this hypothesis, to the ridicule which the author anticipates. This is a topic which has no end. All sorts of conjectures and conceits may be entertained relative to the development of light. Before we leave this branch of our author's theory, however, viz. the setting of light free, we must notice the sufficiently fantastic account given of the mode in which, what we call solar light, is produced :
“ If light,” says the author, “ can be set free by the sudden collision of two gases, as is familiarly illustrated'in chemical experiments, a perpetual fountain of it can be generated at a point where this collision is constantly taking place, between vast masses of gaseous matter thrown off by the sun and earth.” Now, even admitting this incessant strife among the gases-this endless conflict at that “ certain point where the ultimate powers of the sun and earth meet," and admitting that light is set free there in the battle—we apprehend, notwithstanding our author's asserted conviction, that a new theory of light must be formed,” it will be necessary to resort to one of the two rival theories already received, in order to account for the return of the light in its character of " luminousness," back to the earth, from that “ certain focus” where it is thus “set free.”
Thus much for the new theory advanced by this writer. We consider it in many respects fanciful, and unsupported by the great mass of optical phenomena-and, indeed, in some particulars, which it would require too great an extension of our limits to enlarge upon—it is in direct opposition to the results of geometry itself. At the same time, it is but justice to point out some really curious and valuable suggestions, which the author has presented.
One of the difficulties heretofore experienced in the phenomena of vision, has been to explain the mode in which the eye adapts itself to different distances; and while it has been conjectured that an advance or recession of the crystalline lens was the immediate process for this purpose. No satisfactory agency has been detected to produce the motion in that lens. Our writer has discovered that the crystalline lens is attached to something possessing an elastic principle, by which its motions are adjusted and regulated”—and inasmuch as “the retina, with the ciliary processes are the only membranes that answer to this description,” the author concludes that it is by an extension or contraction of these that the crystalline is made to advance or recede. This suggestion is worthy of the nicest examination.
The author's remarks on the “dark angle" of the eye, also merit attention, both as concerns the experiments recorded on that point, and touching the suggestion offered to account for that peculiar phenomenon by the law of interference. We must here however allude to an incidental confirmation, furnished to the ingenious theory of Mr. Horn, by this break in vision; for since the choroides do not cover the base of the nerve, that portion of the posterior surface, will be less adapted to reflect the rays of the inverted image to the anterior surface, as a lookingglass fails to reflect the rays that fall on it where the amalgam may have been rubbed off, and this must occasion a corresponding deficit in the erect images formed by this second reflection, and which Mr. H. supposes to be the images to which sight is due.
There are, beside these, some curious experiments suggested by our author, showing that we can see certain parts of our own eyes. We have been able to discern certain minute bubbles apparently floating in the fluids that lubricate the cornea. But for the rest, there is too much room for illusion and fancy for us to credit what is pretended to be visible, as for instance the choroides, retina, humors, &c.
There are certain notions held by this writer which by many will doubtless be attributed either to an affectation of singularity, or to the ambition of appearing a bold speculatist. For instance, that there is a principle of levity, opposed to the principle of gravity—and a principle of cold, opposed to the principle of heat.
Upon the physico metaphysical part of our author's work, we have but little to say. The scope of all these professed “ discoveries in the mental faculties,” if we rightly understand the author, is to show that the will is useless and impotent, except as the slave of the several organs of sense.
It is true, some novel and sufficiently curious statements are made respecting certain effects of the excited or dormant state of the several external organs of sense. Many of these may be true—and yet the conclusion apparently intended, may be far from being established.
Art. XI.—Lectures on Moral Philosophy, delivered before the
“ Edinburgh Philosophical Society," and Reported for the “ Edinburgh Chronicle." By GEORGE COMBE, Esq. Boston: Marsh, Capen, & Lyon. New-York : Daniel Appleton & Co., 1836.
Though this volume purports to be only a report of Mr. Combe's Lectures on Moral Philosophy, it is evident that the report has b en revised by himself; and is, therefore, to be regarded as a fair expression of his opinions.
Those opinions are entitled to some notice-emanating as they do from one who is looked upon, on both sides of the Atlantic, as the Coryphaeus of phrenology, and who may be supposed, therefore, to represent truly the ethical spirit and tendency of the system.
These lectures are, in fact, but a supplement to the weil known treatise of Mr. Combe on the Constitution of Man-a treatise which has served, more than all his other works, to render the author's name favorably known in the United States. As in that work, so here, he insists at length, and with great earnestness, on the importance of a knowledge of the natural laws. A vast proportion of the evils of human life, according to Mr. C., are chargeable to ignorance alone ; and were such ignorance dispelled, and mankind made familiar with the laws of their own nature and of the external world, and with each as adapted to the other, the result would be not only a vast accession of individual enjoyment, but a rapid approach to a state of universal happiness and purity. The object of these lectures, is to explain and enforce the obligation we are under of respecting these laws in all our relations, as organized, intellectual, and moral beings. Having discovered the nature and functions of any faculty of mind or body, and observed the consequences of exercising it in different degrees of activity, we are enabled to determine the limits which have been prescribed for it; and these limits serve, of course, to measure the duty which we owe in respect to some corresponding object. In this way, we can investigate our personal, domestic and social duties independently of revelation, and ascertain how far the constitution, which God has given us, corresponds with the requirements of his revealed will.
To such investigations, if conducted in the right spirit, there can be no reasonable objection. The written and unwritten laws of God must harmonize ; and we have no fears that science will ever establish any principle which can impair our re