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doubted is this, that rays of light are reflected from, or emitted by every object that is seen ; and that their rays must fall on the retina to make it seen.
73. It is said by an eminent modern philosopher, who is still living, that particles of light pass by any fixed point at the rate of 500 millions of millions of times in a single second ; and that it is by such movements of light, communicated to the eye, that vision is effected. That motion of light at the rate of 482 millions of millions of times produces the sensation of redness; 542 millions of millions of times in a second produces the sensation of yellowpess; and that motion of light at the rate of 707 millions of millions of times in a second produces that of violet.
If it be proved, or must be admitted, that the action of light does make color, is there not a picture of every object seen, on the retina; and how can rays of light passing from that object, make that picture? May it not be that the eye had a power somewhat analogous to the reflection of a mirror; and that external objects pictured on the retina, are, in some incomprehensible manner, reflected to the mind.
Further Proofs from the Senses.
74. The sense of hearing is even less understood than that of vision; the uses of the organs of this sense are more difficult to comprehend ; and it is less easy to make known the little that we do comprehend, by words, or illustrations by drawings. It will be sufficient for the present purpose, that is to prove the certainty of design, or of means used to an end, to advert to a quality of the common air which every one is familiar with, that by exerting the human voice through a common trumpet, it can be sent to a far greater distance than when committed to the air without using such an instrument. The ear has some, but a very slight resemblance to a trumpet inverted. That part which is visible seems to be intended in men, and animals to collect sound, and conduct it inward, until it strikes on a thin membrane, called the tympanum, drawn across the outward end of the barrel or drum of the ear; tympanum is from a Latin word meaning drum.A Between this membrane and an interior one in the hollow of the ear, there are four very small bones which seem to connect the two membranes. The use of these bones, in conducting sound is not known; one of them is connected by one end with the tympanum, and with the second at the other end, and this with the third, and that with the fourth and this with the inner membrane, drawn across another space, and within or behind this meinbrane is a cavity deeply encompassed with the bone of the skull, containing a liquid, wherein the auditory nerve, (from audire, to hear,) proceeding from the brain, develops itself, much in the same way as does the optic nerve in the eye.
75. To have the perception of hearing sound it must pass through the ear to this nerve, and through it the effect is made on the mind. When we consider what the variety and the number of sounds are, which must affect this organ, in the ordinary purposes of life, and its distinguishing power, and its nice adaptation to the end designed, we are left in no doubt as to the intelligence which its mere contrivance required. But however faithfully anatomical investigation may disclose the component parts of the ear, it does not nor can any investigation which art or science has hitherto made, bring the least conception of the nature of hearing to our minds. How sound affects that organization, and how it communicates with the mind is incomprehensible.
76. The commonly received theory of hearing is very unsatisfactory. Particles of air, it is said, being affected by some impulse given by the organs used in speaking, or any other sound-making agent, communi
cate that impulse to adjoining particles of air, and they to others, and so on, until those which are in contact with the tympanum affect it, and thus sound goes to the brain. That air is necessary to the conveyance of sound every where, above the surface of water; and that water is necessary to the conveyance of sound made in water, and that sound glides along the smooth surface of water to a greater distance than it can on the surface of the ground, every body knows. But that sound is nothing but an agitation of the air it is dfficult to believe. When one is speaking to a numerous assembly in a large apartment, he may make himself distinctly heard, and understood, even in the most rapid and minute articulation of which he is capable, by those persons who are most remote from him. But no effort of his lungs would 'affect in the least degree the lightest substance which floats in the air, at one half, or perhaps one quarter, of that distance. So one may make a violent agitation of all the air in a large apartment by swinging a door backwards and forwards, but he will make thereby no sound. Sound can be made to pass from one apartment to another, through a solid wall, and when the air on one side of it cannot receive any impulse from the air on the other. Sound passes through wood, metals, and other substances, with far greater rapidity than through air or water. And through some it cannot pass.
77. Is there then something in nature, hitherto unknown, which is sound; as there may be something, which is vision? That human ingenuity has gone no further as yet, in the philosophy of sound and vision, is no reproach to it. Looking back on its inventions and discoveries, it would be some reproach to it to assume, that it has attained its utmost limits on these subjects.
78. The other senses must be passed over with a few words. That of feeling seems to be diffused throughout the system. The sensation is always local, whether in the extremities, in the organs of sense, or in the brain itself. So also tasting and smelling are local. The connexion between these and the mind is
alike hidden from us. The only peculiarity between these three senses, and those of seeing and hearing is, that as to the three former, perception has a locality in the system, that is, feeling is every where, tasting is in the organs of taste, smelling is in the organs assigned to give that perception, but the organs of seeing and hcaring give no organic sensation, and we only learn from experience that it is the eye that sees, and the ear that hears. In these truths we have one more proof of the Intelligence which framed us. The action of the eye and of the ear depends upon no volitions of our own. If they were physically touched by the objects which they convey notice of to the mind, as the other senses seem to be, would they not from their wonderful complication and delicacy of structure, soon wear out, and become unfit for their offices ? "Is there not something which may be called intellectual in the action of these two senses? But these are inquiries not necessary to the present purposes, if they are deserving of any notice.
79. If the purpose in view thus far has been sufficiently accomplished, to make that purpose understood, it has been shown, that there is a created material universe, of which man constitutes a part. That he is curiously and wonderfully prepared and designed to act on this universe, and that it is in like manner prepared and designed to act on him. There is reason to believe from what we know him to have been able to do in relation to this material system, that there is no part of it with which he cannot connect himself to some useful purpose. Surely this is true as to all things and beings on earth to which he has access. It is even true as to the far distant luminaries of the firmament. He has made himself acquainted with the laws which govern them. He has made them, millions of miles from him as they are, minister to his necessities, his wants, and his pleasures. They make known to him the precise point on which he happens to be on the surface of his own little globe, the existence of which is perhaps unnoticed and unknown to the intelli-.
gent beings who may inhabit them. They have served him to enlarge his mind, to invent rules of science, , and they have served him to elevate his conceptions, and to raise himself to that high station in the scale of being, mortal as he is, which permits him to know and to adore and to render his humble tribute to the infinite and awful Mind, of whom, and through whom, all things are ordained.
80. We have endeavored to find man's place in the material world. We have next to consider him in his intellectual character. In this respect it will appear that his material formation, and that of his mind, have an intimate and necessary connexion. Whatever the mind may be, and in whatsoever manner it is connected with its material dwelling place, it does not display its powers until it has been acted upon by the senses. This fact has led to the belief of the materiality of the mind, and has been the subject of many refined discussions. It is certain that the physical and mental action of one human being, is known to any other by and through the senses only. These truths force on us the necessity of considering the action of the senses in connexion with, and inseparably from, what is known of the qualities of the mind. This will be found to be at best a very limited knowledge.
81. The human mind has been the subject of many learned works. These have been given to the world at different periods. · Each successive author has had the opportunity of studying the theories of his predecessors, and of adopting, modifying, disproving or rejecting them, and of attempting to establish his own.