[Footnote 44: Sommerville's Connexion, etc., § xxix. p. 339. Carpenter's Manual of Physiology, § 932.]
Again, (2.) sensations arising from those impressions are so exceedingly complex, that we attribute many more of them to each separate sense than really belong to it. By habit we have become so much accustomed to associate several of those impressions together, as to be unable, without difficulty, to analyze them, and to separate the simple results of the sensuous impression from the more complicated judgments which experience and reason add to it, and by which they interpret it. The eye, for example, receives and conveys impressions purely and solely of light, and its absence, including those of color, which belong to light. Form, extension, sense of distance, etc., are no part of the simple impression made upon the eye, and through it upon the mind, further than they influence the condition of the light, as by bounding it, shading it, etc. These belong exclusively to the sense of touch, combined with experience, so as to be suggested, without actual contact, by certain conditions of light. An inexperienced eye, looking for the first time at a plain surface, as a disc, or at a cube, or a ball, would see only the color, and the edges where that changed. It could not enable the mind to judge how far the object was distant; nor why the light and shade were differently disposed in each; why the light reflected from the disc was uniform, and bounded by a circle, while that from the ball was softly shaded, though bounded by a circular line similar to the disc; nor why the light coming from the cube was divided and bounded by straight lines and sharp angles. To judge of these peculiarities, and their meaning, touch must come to the aid of sight; and afterward memory will recall the conclusions of former experience; and comparison will enable the reasoning mind to form a judgment regarding the shape, size, and distance of the object. In a similar manner, the organs of hearing convey impressions of sound alone; distance, direction, exciting cause, are quite out of the province of its information. Sight and touch, and experience and judgment, all enter into the complex information, now communicated to a practiced observer. This fact is strikingly exemplified in musical sounds. A skillful musician will tell you the notes and chords composing a series of such sounds, in which an uninformed and unpractised ear will be able to detect nothing but concord or this court. Thus Mozart, at two hearings, was able to note down the score of Allegri's Miserere. Thus, too, there are many substances which we of [{259}] by taste, as it is supposed, but which are in reality operative on the sense of smell. For instance, if the nose is held while eating cinnamon, we shall perceive no difference between its flavor and that of a pine shaving. [Footnote 45] The same fact is observed with regards to many aromatic substances: if held in the mouth, or rubbed between the tongue and the palate, the nostrils being all the while dosed, their taste is hardly, if at all, recognized; but it is immediately perceived on reopening the nasal passages. Thus, too, the wine-taster closes his mouth, and sends the aroma of the wine through his nostrils. Other substances, again, there are, neither aromatic nor volatile, taste very strongly irritates the mucous membrane both of nose and tongue, as mustard does, for example, just as it would the skin, if applied long enough externally. Such a sensation, therefore, as the taste of mustard, evidently belongs to the organs of touch, differing in degree of sensitivity only. Hence we are taught that the substances properly the objects of the sense of taste, are those only which produce sensations purely and exclusively gustative, perceived neither through the nose nor through the nerves of touch, but acting on the tongue and palate only. Salt, sugar, quinine, tannin, and citric acid, types of the saline, saccharine, bitter, astringent, and sour, are said to possess sapid properties. [Footnote 46] From these simple considerations it appears undoubted that the province of each separate organ of sensation, and its resultant impressions on the mind, are much limited, when compared with the wider empire attributed to them by popular language and opinion. Reason is ever correcting and enlarging the simple impression, adding the conclusions of experience and judgment and comparison to the primary suggestions of the sensation; making allowances for what is faulty or imperfect; measuring circumstances, and comparing all the conditions of the impression with each other, before even an approximately true result can be arrived at.
[Footnote 45: Herschel's Discourse on the Study of Natural Philosophy, § 72.]
[Footnote 46: Carpenter's Manual of Physiology, § 945.]
Further (3.) there is much in nature of which the senses totally fail in giving us any information whatever. "None of the senses," says Sir J. Herschel, "gives us direct information for the exact comparison of quantity. Number, indeed, that is to say, integer number, is an object of sense, because we can count; but we can neither weigh, nor measure, nor form any precise estimate of fractional parts by the unassisted senses. Scarcely any man could tell the difference between twenty pounds, and the same weight increased or diminished by a few ounces; still less could he judge of the proportion between an ounce of gold and a hundred grains of cotton by balancing them in his hands." [Footnote 47] Nay, even in their own proper and peculiar province, the senses are singularly deficient in certain kinds of information, especially when comparison is involved. "The eye," says the same high authority, "is no judge of the proportion of different degrees of illumination, even when seen side by side; and if an interval elapses, and circumstances change, nothing can be more vague than its judgment. When we gaze with admiration at the gorgeous spectacle of the golden clouds at sunset, which seem drenched in light, and glowing like flames of real fire, it is hardly by an effort we can persuade ourselves to regard them as the very same objects which at noonday pass unnoticed as mere white clouds basking in the sun, only participating, from their great horizontal distance, in the ruddy tint which luminaries acquire by shining through a great extent of the vapor of the atmosphere, and thereby even losing something of their light. So it is with our estimates of time, velocity, and all other matters of quantity; they are absolutely vague and inadequate to form a foundation for any exact conclusion." [Footnote 48]
[Footnote 47: Discourse on the Study of Natural Philosophy,§ 117.]
[Footnote 48: Discourse on the Study of Natural Philosophy,§ 117.]
Again (4.) there is a large class of phenomena whose causes, and even whose existence, are far too remote or too minute to be revealed to us by our senses. What are telescopes and microscopes, but the means which science ingeniously devises to supply this innate and irreparable deficiency of our organs of sense? Satirists of the middle age, and its scholatic philosophers, have said that they would dispute as to the number of spirits that could dance on the point of a needle. Modern science shows us, in the infusoria, animals of perfect formation, endowed with functions suited to their condition, many thousands of which could pass at once through the eye of the finest needle; a million of which would not amount in bulk to a grain of sand. No less wonderful is the world of minute existence, revealed by the microscope, in a drop of stagnant water. It is a world within itself, an epitome of the earth, and its successive geological races. A variety of microscopic creatures make their appearance, and die; in a few days, a new set succeeds; these disappear in their turn, and their place is occupied by a third race, of a different kind from either of the former—the remains of all of them lying at the bottom of the glass. [Footnote 49] "If for a moment," says Humboldt, "we could yield to the power of fancy, and imagine the acuteness of our visual organ to be made equal to the extreme bounds of telescopic vision, and bring together that which is now divided by long periods of time, the apparent rest which reigns in space would suddenly disappear. We should see the countless hosts of fixed stars moving in thronged groups, in different directions; nebulas wandering through space, and becoming condensed and dissolved like clouds, the veil of the milky way separated and broken up in many parts, and motion ruling supreme in every portion of the vault of heaven, even as on the earth's surface, where we see it unfolded in the germ, the leaf, and the blossom, the organisms of the vegetable world. The celebrated Spanish botanist, Cavanilles, was the first who entertained the idea of 'seeing the grass.' He directed the horizontal micrometer threads of a powerful magnifying glass at one time to the apex of the shoot of a bambusa, and at another, on the rapidly growing stem of an American aloe, precisely as the astronomer places his cross of network against a culminating star." [Footnote 50] Without speculating so deeply in what is distant and hidden, the very atmosphere in which we live and breathe is imperceptible to every one of our senses, except, indeed, when viewed through its whole depth, to that of sight in the blue color of the sky, or indirectly to that of touch, by the resistance which it offers to the hand, or the face, in passing rapidly through it, or when it is set in motion by the wind. We perceive its effects, indeed, in the modifications which the phenomena of light and sound undergo, in consequence of its action upon them; in the barometric column, and in a thousand other physical and chemical agencies which attest the presence of the atmosphere, and the important functions which it performs in our terrestrial economy. But as far as sight or hearing, taste or smell, are affected by it, directly, it has absolutely no existence.
[Footnote 49: Somerville's Physical Geography; II., xxxii. 348, note.]
[Footnote 50: Cosmos, I. 189, 40.]
Modern science, indeed, coming to the aid of the senses, can enable them to attain the results of an almost inconceivable acuteness. Thus while quantity and comparison are inappreciable, or nearly so, by the unaided organs of sense, balances have been constructed with a sensibility so exquisite, as to turn with the thousandth part of a grain, and yet pretend to no extraordinary degree of merit. [Footnote 51]
[Footnote 51: Herschel's Discourse on the Study of Natural Philosophy, § 338.]