BOOKS.

PROFESSOR TYNDALL ON SOUND.*

PROFESSOR TYNDALL is not merely a man of science. He is that in the most delicate sense of• the word. But if his science is great, his art is yet greater. Perhaps it would not be unfair to say that Professor Tyndall's reputation, however eminent, is below his real merit ; but that his merit and peculiar distinction lie not so much in his being a man of science, as in being a Scientific Artist. We beg to explain our meaning a little further, as it belongs to the essence of our criticism. Our meaning is not that Professor Tyndall is an elegant writer. There is a large class of professional men here belonging to almost every profes- sion, whose great ambition is to write ornately and with elegance, each in his own department. It is no small literary treat to study with an unprofessional eye the laborious elegance—elegance for the sake of being elegant—with which professional men's books in this country literally teem. Nothing can be more fluent than their periods, nothing more suave than their idioms, nothing more distantly decorous than their choice of expressions. Professor Tyn- dall is none of these. His art is not in his style. His style, it is true, is perfect. His art is in his science. That his style is perfect, Pro- fessor Tyndall himself is not in the least aware. He could not be so. It would cease to be perfect the moment he gave it a thought. It sits so closely to his subject, each word expresses so exactly what he means to say, he is so unconsciously and irresistibly impelled to take the nearest word, be it long or short, simple or sonorous, which lies nearest to his idea, that the result is a miracle of light, energy, and grace. This is, no doubt, saying much ; but if any one thinks it too much, we can only say, ' Read the book yourself.' But even what we have said is not all what we mean when we say that Professor Tyndall is an artist. We mean that he has gone beyond the mere mastery of his subject, that in his hand science ceases to

• Sound. A Course of Lectures. By John Tyndall, LL.D., F.B.S. London: Longmans.

be a mere logical chain of propositions clearly apprehended, and becomes a new realm of actual perception, in which truths and facts, unseen to the naked eye, yet live and move and have a corporeal being and reality, clothed by the professor in imagery, which is, in fact, a living embodiment of science, without in any sense being a romance. His powers of illustration and distribution are prodigious, but his illustrations are due not to the vagueness, but the perfect grasp and knowledge of his subject, they spring out of its essence, not from its surface. Few men have proved more splendidly than Professor Tyndall the truth of the profound obser- vation of Laplace, in his preface to his doctrine of chances, that " what we call metaphors are in fact identities."

Take as an instance Professor Tyndall's illustration of a wave of sound. Of all the mystical and transcendental ideas that can be presented to the untutored mind, probably that of the undulatory theory of sound can hardly be surpassed. Professor Tyndall makes the subject visible to the commonest understanding, by means of anything that falls under his hand, a few boys picked up in the streets, or a few

balls in a game of solitaire. Sound, no less than light, no less than heat, is motion,—motion transmitted to a peculiar

system of nerves,—the auditory system. Sound is sonorous motion, and the sonorous motion is in fact a sonorous wave, or pulse, propagated from particle to particle of the air until the last particles, the particles nearest the ear, impinge upon the tympanic

membrane, causing it to shiver. The tremors are transmitted to the auditory nerve, and along the auditory nerve to the brain, where it announces itself as sound. But how is this motion, this wave, to be realized and made visible to the understanding? We quote Professor Tyndall's own words :— " Let me endeavour to illustrate the propagation of sound by another homely but useful illustration. I have here five young assistants, A, B, C, D, and E, placed in a row, one behind the other, each boy's hands resting against the back of the boy in front of him. E is now foremost, and A finishes tho row behind. I suddenly push A ; A pushes B, and regains his upright position ; B pushes C ; C pushes D ; D pushes E ; each boy, after the transmission of the push, becoming himself erect. E, having nobody in front, is thrown forward. We could thus transmit a push through a row of a hundred boys, each particular boy, however, only swaying to and fro. Thus, also, we send sound through the air, and shako the drum of a distant ear, while each particular particle of the air concerned in the transmission of the pulse makes only a small oscillation."

Professor Tyndall adds :— " Scientific education ought to teach us to see the invisible as well as the visible in nature, to picture to the eye of the mind those operations which entirely elude the eye of the body ; to look at the very atoms of matter in motion and at rest, and to follow them forth, without ever once losing sight of them, into the world of the senses, and see them there integrating themselves in natural phenomena. With regard to the point now under consideration, you will, I trust, endeavour to form a definite image of a wave of sound. You ought to see mentally the air particles when urged forwards crowding closely together, but imme- diately behind this condensation you ought to see the particles separated more widely apart. You ought, in short, to be able to seize the connec- tion that a sonorous wave consists of two portions, in the one of which the air is more dense, and in the other of which it is less dense than usual. A condensation and a rarefaction, then, are the two constituents of a wave of sound."

What Sir Isaac Newton did for science by popularizing —that is to say, by exhibiting, as it were, to the naked eye—the behaviour of infinitely small quantities in the generation of curves,—Professor Tyndall does by exhibiting also, as it were, to the naked eye the behaviour of atoms in the generation and transmission of heat and

sound. Nor is it less wonderful after its kind that the ultimate element of a curve at any point should be the tangent, than that the ultimate element of a wave of sound should be motion, namely,

the infinitesimal impact and recoil of a material atom. The wave moves on, the particle remains where it was. Nature herself had given or suggested the concrete integers, each roughly in its kind and as a whole. Each of these rough suggestions also gave rise to its own abstract and perfected idea or definition. Thus nature showed us approximate circles and other mathematical curves, which led to the ultimate elaboration of the idea of the hypothetically perfect forms, supposing them capable of actual existence in that perfection. A perfect circle in nature is impossible, geometrically speaking. But nature showed us enough to enable us to arrive at the artificial concep- tion of that which a perfect circle would be if material obstacles could be eliminated. What nature did not show to the naked eye

was the elemental generation in each case and the ultimate ele- ment. This, when discovered, often turned out to be, sometimes apparently, sometimes in reality, wholly opposed, or utterly foreign, to the popular ideas which had gradually grown round the in- tegrated whole. To accustom the mind to realize the tangent as the ultimate element of the curve requires a slow, and it

may even be said an organic transformation in the usual habits of the untutored mind. So nature showed us the wave in its grandest form, and, of course, always in con- nection with motion. But the ideas to which the motion actually seen gave rise were scientifically false, so far as that motion was supposed to have anything to do with the motion essential to the wave itself as distinguished from that of the tide. The tides move forward, and so do the waves ; but each in virtue of different motions. In the first, the particles of water are borne along with the current. In the second, the particles of water remain sta- tionary, subject only to the vibration, while the wave itself, trans- mitted by the vibrating particles, moves forward with varying velo- city. The first is a motion of translation ; the second a motion of transmission. It is the entanglement between these different motions which makes the scientific idea of the ordinary wave so difficult to the popular apprehension, even where the whole operation is visible to the naked eye. But where, as in the case of heat and sound, the wave is not visible, it is all the greater feat to bring it as a picture before the mind. And this Professor Tyndall does with an art which throws even his science into the shade. This is not the place to enter upon all the delicate and abstruse experiments which crowd Professor Tyndall's lectures. Whatever he touches he illumines, and it would have been equally easy to have illustrated his art by examples more remote from popular use. We purposely chose the fundamental conception which lies at the threshold of the subject, namely, the Wave, because the general familiarity with the concrete effect in common life would throw a more vivid light upon the scientific dissection of the abstract idea.

Of course the discussion of the phenomenology of sound is accom- panied throughout with a tacit commentary and disquisition in the mind of the reader on the relation between the objec- tive and the subjective side of the subject, on the external or purely physical laws of a certain vibratory system, and on the internal or physiological laws regulating the effect of that scheme of vibration on the nervous organism. The latter, again, divides itself into a formal and an withetical branch. The formal branch would embrace the purely mathematical forms of sound. Such forms as those, for instance, illustrated by the figures produced by Mr. Wheatstone's kaleidophone, by Chladni's square plates, and by Lissajou's method of giving optical expres- sion to the vibration of a tuning fork. These we call formal partly because their forms are more or less mathematically perfect, and because they have no further connection with the msthetical branch of sound, than the forms of the kaleidoscope and the vibra- tions of mathematically perfect colours have with the mstheti- cal branch of perception, namely, painting and sculpture. In this view, although the mathematical theories, both of sound and colour, are advancing by certain and demonstrative steps every day, there remains a gulf between these theories and the aesthetics of painting and music. The colours which we see in the spectrum or through a prism have no direct relation to art. In fact, they are excluded from it. An artistic painting does not even admit them. So in music perfect sound is ex- cluded. There is no note which is played upon any instru- ment within the range of art which is ever mathematically perfect. A more perfect note can be got out of a basin of glass half filled with water by lightly rubbing the edge with a wetted finger, than can be got out of the most beautiful violin. But such sound finds no place in music, any more than prismatic colour finds a place in painting. A symphony of Beethoven in this respect stands on exactly the same footing as a picture of Titian. The law, therefore, that the combination of two notes is more pleasing to the ear the smaller the two numbers which express the ratio of their vibrations, has no very direct bearing on musical art. The perfect octave is no doubt the most perfect conso- nance, and as such, is prettier than the perfect fifth, which in its turn is prettier than the fourth, the third, and the sixth. But "prettiness" in the sense of mathematical perfection, however that perfection may be defined, rarely enters, nay, is mostly excluded from art proper. No doubt the gorgeous colours in a chemist's shop window have a physical effect on the eye which the finest picture would fail to produce. But mere colour and gems are not art. So neither is sweetness of sound music—always remembering that we are not speaking here of that beauty of tone and touch belonging to the various instruments respectively. In painting it is possible for a picture to be beautiful, and yet composed of colours each of which, taken separately, is not agreeable to the eye. In like meaner, a piece of music which aimed at multiply- ing " prettiness" of sound—namely, that which in itself alone is sweetest to the ear—would tend to become a jingle of mere physical sweetneeses and sugar-plums, and in so far depart from true art.

And this is the distinction, no doubt, between educated and uneducated musicians. The former require higher beauties, the latter remain within hail of the mere jingle of sweetness. In this view octaves and fifths and fourths and thirds cease to have any beauty of their own, save as they minister to an integral conception in which they appear only to disappear. The discords of Beethoven have an effect upon the musical organization as far above the jingle of prettiness as the passion of Othello surpasses the piping of a bullfinch. This, of course, is not in any sense addressed to Professor Tyndall. His account of Helmholtz's in- vestigation into the laws of consonance and dissonance is extremely valuable and entertaining both as a contribution to the popular literature of a most abstruse science, and also as a very quaint commentary up% Euler's views respecting the preference of the human soul for sweet simplicity. Nevertheless, we must with all deference ask whether, as a matter of fact, the law laid down, namely, that in all cases the consonance which is represented by the simpler arithmetical ratio is pleasantest to the ear is actually true in all cases ? This is by no means a random and idle question. Thus the ratio for a musical fourth is 3 : 4, that is to say, the vibra- tions of any note and the musical fourth above it are as 3 : 4. The ratio for a major third is 4 : 5. Now 3 : 4 is a simpler ratio than 4 : 5, and therefore according to the law the musical interval corresponding to the former, namely, a fourth, ought to be more pleasant, merely as sound, to the ordinary ear, than the interval which corresponds to the latter, namely, a third. As a matter of fact, is this true ? It is certainly not true in the case of the present writer. In his case even the sixth, whose ratio is five-thirds, is pleasanter than a fourth, whose ratio is three-fourths, and has always been so from his earliest child- hood. lie can remember quite distinctly that as a child the fourth scarcely seemed to him musical at all. This might be idiosyncracy. But we question if twenty children were made to listen to a third and a fourth in succession, and asked which they preferred, whether the majority would not vote for the third. Supposing this to be true, the exception to the rule would still have to be accounted for. We make this suggestion to Professor Tyndall with all deference. In conclusion, we are happy to be able to inform our readers, especially those who, when asked if they like music, invariably answer, " I don't play," that they them- selves possess, it would seem, a labyrinthine instrument, which is being played upon, and to which they listen all day. This instru- ment carries, it appears, 3,000 strings, lies inside their own ears, and with all respect to the great Mr. Broadwood, is even more miraculous than his own miraculous instruments.