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CHAPTER VL

SOUND.

THE NATURE AND LAWS OF SOUND-TWO SOUNDS PRODUCING SILENCE -THE CALLS AND SONGS OF BIRDS-THE MUSIC OF NATURE-THE ROAR OF STORMS-DIVERSITIES OF SOUND IN DIFFERENT POSITIONS AND CIRCUMSTANCES OF AIR AND LAND-SONOROUS CURRENTS THROUGH GORGES, CREVICES, AND NATURAL APERTURES-MUSICAL ROCKS AND MOUNTAINS-ECHOES.

WHAT sound is, we do not certainly know. It is commonly said to be vibration of the air, produced either directly in the air itself, or indirectly through some other elastic substance, and acting mechanically "on the organism of the ear. And it may be so. But assuming light to be a subtle fluid, sound may be a subtle fluid too, diffused through all vibrative substances, silent when in repose, and sonorous when put in motion. This theory is countenanced by several strong facts and reasonings; yet the common one serves perfectly well to explain all the known properties and laws of sound. And whichever be correct, the ear and the vibrating air are related to each other as certainly and intimately as the eye and the undulating light. Were there no ear or no atmosphere, or were ear and atmosphere differently related to each other than they are, we could have no acquaintance with the delights of voice and song, of speech and music, of the orchestra of human utterance, of the

hallelujah of winds and waters and all vocal nature ever praising God.

Sound travels through hydrogen gas at the rate of 3000 feet per second, through water at the rate of 4708 feet, through tin at the rate of 8175 feet, and through glass and iron at the rate of 18,530 feet, but through the atmospheric air, in its ordinary or average conditions, at the rate of only 1142 feet. A series of sounds, following one another at the rate of not fewer than sixteen in a second, form a continuous sound; and, when of exactly similar kind, and following one another at regular intervals, they form a musical sound. The strings and orifices of musical instruments produce musical sounds simply by making uniform and regular series of vibrations; and they owe their respective pitch and power to the comparative velocity of their action. Sounds whose vibrations occur in precise ratios to one another, are harmonies; and two whose vibrations occur in the proportion of one to two, or of fifty to a hundred, are unisons. All other sounds than these we have named are noises and discords.

But we are not here dealing with the theory of music; we must not be tempted to dally with the wonders of the musician's art, no matter that these are so mightily fascinating and so surpassingly lovely; and we shall only notice, in the words of Sir David Brewster, what he calls "a property of sound with more of the marvellous in it than any result within the wide range of the sciences"-the property of producing silence by the joint action of two loud musical sounds. "If two equal and similar strings, or the columns of air in two equal and similar pipes, perform

exactly 100 vibrations in a second, they will produce each equal waves of sound, and these waves will conspire in generating an uninterrupted sound, double of either of the sounds heard separately. If the two strings or the two columns of air are not in unison, but nearly so, as in the case where the one vibrates 100, and the other 101 times in a second, then at the first vibration the two sounds will form one of double the strength of either; but the one will gradually gain upon the other, till at the fiftieth vibration it has gained half a vibration on the other. At this instant the two sounds will destroy one another, and an interval of perfect silence will take place. The sound will instantly commence, and gradually increase, till it becomes loudest at the hundredth vibration, where the two vibrations conspire in producing a sound double of either. An interval of silence will again occur at the 150th, 250th, 350th vibration, or every second, while a sound of double the strength of either will be heard at the 200dth, 300dth, and 400dth vibration. When the unison is very defective, or when there is a great difference between the number of vibrations which the two strings or columns of air perform in a second, the successive sounds and intervals of silence resemble a rattle. With a powerful organ the effect of this experiment is very fine, the repetition of the sounds wow-wow-wow representing the double sound and the interval of silence which arise from the total extinction of the two separate sounds."

The calls and songs of birds rank high among the delights of nature, and not less high among its wonders. None, indeed, are wildly tumultuous or bewilderingly elaborate; but some are grandly piquant,

some sublimely strong, like the serene influence of the sky, some gloriously beautiful, some cheering and melting and mighty over all minds; and the whole, by their aggregate richness and their endless variety, constitute a museum of sound whose strokes and rhythms have ever been the profound study of the Handels, and Mozarts, and Beethovens, and all other masters of melody. Even the most familiar have a witchery which affects all men except the most brutal, and is as evidently a provision of the Beneficent Creator to charm the ear, as colours or clouds or flowers are to charm the eye. Think, for example, of the trombone of the cormorant, the "shrill clarion” of the domestic cock, the chuck-chuck of the domestic hen, the cawing of the rook, the chatter of the magpie, the clatter of the fern-owl, the loud laugh of the woodpecker, the cooing of the dove, the peewit of the plover, the cuckoo of the summer-herald, the calls and chirrups of the common hedge-birds, the melodious chink-chink of the blackbird, the flute-like melody of the blackcap, the soft, plaintive, liquid song of the nightingale, the mellifluous thrill of the lark in the air and the throstle on the tree, the carolling woodnotes and throbbing lays of warblers and finches.

"Sweet birds, that breathe the spirit of song,

And surround heaven's gate in melodious throng-
Who rise with the early beams of day,

Your morning tribute of thanks to pay:

You remind us that we should likewise raise

The voice of devotion, and song of praise;

There's something about you that points on high,

Ye tuneful tenants of earth and sky."

But, as a periodical writer beautifully remarks,

"Nature seems to have mingled harmony in all her works. Each crowded and tumultuous city may properly be called a temple of discord; but, wherever Nature holds undisputed dominion, music is the partner of her empire. The 'lonely voice of waters,' the hum of bees, the chorus of birds-nay, if these be wanting, the very breeze that rustles through the foliage, is music. From this music of Nature, solitude gains all her charms; for dead silence, such as that which precedes thunder-storms, rather terrifies than delights the mind:

'On earth 'twas yet all calm around,
A pulseless silence, dread, profound-
More awful than the tempest's sound.'

"Perhaps it is the idea of mortality, thereby awakened, that makes absolute stillness so awful. We cannot bear to think that even Nature herself is inanition; we love to feel her pulse throbbing beneath us, and listen to her accents amid the still retirements of her deserts. That solitude, in truth, which is described by our poets as expanding the heart and tranquillising the passions, though far removed from the inharmonious din of worldly business, is yet varied by such gentle sounds as are most likely to make the heart beat in unison with the serenity of all surrounding objects. Thus Gray

'Now fades the glimmering landscape on my sight,
And all the air a solemn stillness holds,
Save where the beetle wheels his droning flight,

And drowsy tinklings lull the distant folds!'

"Even when Nature arrays herself in all her terrors, when the thunder roars above our heads, and man, as

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