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in nature, but it is also among the best illustrations of the decomposition of light. The mode in which it is produced is not very difficult to understand. Suppose A D to be a drop of rain, on which a ray of sunlight falls in the direction B A. It will I^g. 57.
be refracted to
wards the per- --^A—
lours, which will ^><&^/
cordiDg to their refrangibility. Suppose the red ray, after refraction, to proceed to C. From C it will be reflected to D, and thence, after another refraction, it will proceed towards E. An eye placed at E, therefore, will see a red image of the sun in the direction of F. The same eye will perceive a violet image formed by some drop or drops a little below AD, and, in the same way, the intervening drops will send towards E rays of orange, yellow, green, blue, and indigo. Thus, within a certain space in the raincloud, all the colours will appear, and in the same order as in the prismatic spectrum, except that the violet will be downwards. It will be observed that the sun is supposed to be in the direction AB at the time when the rainbow appears. The red image is seen in the direction EF, which makes a certain angle with A B. Now if we trace out a circle in the sky, such that a line drawn from the eye to any point of it shall make the same angle with AB that E F does, it is obvious that rain-drops in Tiny part of that circle will give forth red light. Thus an arch of red light will be seen in the rain-cloud. In the same way there will be an orange arch, a yellow arch, and so on; in short, there will be a rainbow. Even a second rainbow may frequently be seen, faint and shadowy, outside the first. It is accounted for exactly in the same way, except that the rays which form it are twice reflected.
Hence this splendid phenomenon, so brilliant, so spacious, so ethereal, so deeply associated in our fancy with all that is bright and heavenly, is found to be the simple offspring of rain and sunshine. We are taught in Scripture to regard it as the symbol of God's gracious promise, that He will no more destroy the earth's inhabitants by a deluge. But it is only by His special appointment, and not from anything in its own nature, that it possesses such a significance. In itself, it tells only of light shining upon drops of water, and of the gorgeous hues which that light contains. It is connected, in its physical causes, with the greenness of the grass, the varied beauty of flowers, the gay plumage of birds, the glories of a summer sunset, and every other display of those magnificent colours which lie concealed in the sunlight, till they are extracted from it for our enjoyment and delight.
QUESTIONS FOR EXAMINATION.
What do we know of the nature of light? State two opinions. Give examples of luminous bodies. What is ether supposed to be? How is the velocity of light ascertained? What is its velocity? What is a ray of light? a pencil of light? a shadow? How do we see bodies which have no light in themselves? How is the light of the sun so universally diffused? What is meant by the "reflection" of light? What are mirrors made of? What are spcculaf Explain the great law of reflection. Give examples. Show how images are formed in a plane mirror. What is remarkable about the images formed by a concave mirror? What is meant by the focus of a mirror? Show that the quantity of light reflected at any surface is variable. What is refraction? Trace the course of a ray through a sheet of plane glass. How is the apparent depth of water affected by refraction? Explain the experiment of the coin and basin. Why does a rod dipped slantingly in water appear crooked? What atmospheric effects are due to refraction? What are lenses? Divide them into two classes, and explain the effects of each. How is light shown to be compound? Describe the spectrum. To what are the colours of natural objects attributable? Show that they are not in the objects themselves. How is the rainbow formed? Wiry is there sometimes a second rainbow? Why do we see an arch of colours, and not simply a spectrum?
BERKARDO DE CAEPIO.
[don Sancho Couht Saldasa of Spain had been imprisoned by King Alphonso of Asturias; and his son, Bernardo de Carpio, on coming of age, took up arms to effect his father's release. A long war ensued, and Alphonso at length promised to release the Count on condition that Bernardo should deliver up to him his castle of Carpio. To this Bernardo consented, and surrendered the castle. But in the meantime the treacherous king had caused Count Saldana to be slain, and his dead body to be placed on horseback, to deceive for a time his dutiful son.]
The warrior bowed his crested head, and tamed his heart of fire,
"Rise! rise! even now thy father comes, a ransomed man this day;
And lo! from far, as on they pressed, there came a glittering band,
His dark eye flashed, his proud breast heaved, his cheek's blood came and went;
He reached that grey-haired chieftain's side, and there dismounting bent;
A lowly knee to earth he bent, his father's hand he took:—
That hand was cold—a frozen thing—it dropped from his like lead,
He met at length his father's eyes, but in them was no sight!
Up from the ground he sprang, and gazed; but who can paint that gaze?
Thev hushed their very hearts who saw its horror and amaze:
"Father!"at length he murmured low, and wept like childhood then—
(Talk not of grief till thou hast seen the tears of warlike men)— He thought on all his glorious hopes, on all his high renown; Then flung the falchion from his side, and in the dust sat down.
And, covering with his steel-gloved hand his darkly mournful brow,
"No more, there is no more," he said, "to lift the sword for now; Aly king is false! my hope betrayed! my father—oh, the worth, The glory, and the loveliness, are passed away from earth!"
TJp from the ground he sprang once more, and seized the monarch's rein.
Amid the pale and wildered looks of all the courtier train;
And with a fierce, o'ermastering grasp, the rearing war-horse led,
And sternly set them face to face, the king before the dead.
"Came I not forth upon thy pledge, my father's hand to kiss? Be still! and gaze thou on, false king! and tell me what is this? The voice, the glance, the heart I sought—give answer, where are they?
If thou wouldst clear thy perjured soul, send life through this cold clay!
Into these glassy eyes put light—be still, keep down thine ireBid these white lips a messing speak—this earth is not my sire! Give me back him for whom I strove, for whom my blood was shed;
Thou canst not—and a king!—his dust be mountains on thy head!"
He loosed the steed—his slack hand fell;—upon the silent face
His hope was crushed—his after-fate untold in martial strain—
A SHIP SINKING.
Her giant form, o'er wrathful surge, through blackening storm, majestically calm, would go 'mid the deep darkness, white as snow! But gently now the small waves glide, like playful lambs o'er a mountain's side. So stately her bearing, so proud her array, the main she will traverse for ever and aye. Many ports will exult at the gleam of her mast;—Hush! hush! thou vain dreamer!—this hour is her last!
Five hundred souls, in one instant of dread, are hurried o'er the deck; and fast the miserable ship becomes a lifeless wreck! Her keel hath struck on a hidden rock, her planks are torn asunder, and down come her masts with a reeling shock, and a hideous crash, like thunder! Her sails are draggled in the brine, that gladdened late the skies; and her pennant, that kissed the fair moonshine, down many a fathom lies. Her beauteous side3, whose rainbow hues gleamed softly from below, and flung a warm and sunny
flush o'er the wreaths of murmuring snow, to the coral rocks are hurrying down, to sleep amid colours as bright as their own.
Oh I many a dream was in the ship an hour before her death; and sights of home with sighs disturbed the sleeper's long-drawn breath. Instead of the murmur of the sea, the sailor heard the humming tree, alive through all its leaves;—the hum of the spreading sycamore that grows before his cottage door, and the swallow's song in the eaves. His arms enclosed a blooming boy, who listened, with tears of sorrow and joy, to the dangers his father had passed; and his wife—by turns she wept and smiled, as she looked on the father of her child returned to her heart at last! He wakes at the vessel's sudden roll, and the rush of waters is in his soul! Astounded, the reeling deck he paces, 'mid hurrying forms and ghastly faces;—the whole Bnip's crew are there! Wailings around and overhead—brave spirits stupified or dead—and madness and despair!
Now is the ocean's bosom bare, unbroken as the floating air; the ship hath melted quite away, like a struggling dream at break of day. No image meets my wandering eye, but the new-risen Bun and the sunny sky. Though the night shades are gone, yet a vapour dull, bedims the wave so beautiful; while a low and melancholy moan mourns for the glory that hath flown!
ON THE DOWNFALL OF POLAND.
Oh! sacred Truthl thy triumph' ceased a while,
Warsaw's last champion, from her height' surveyed,
He said, and on the rampart heights' arrayed
In vain, alas! in vain, ye gallant few!