immediately behind the pupil, and through which all the light entering the eye must pass. The cavity between this lens and the retina is filled with a transparent fluid, and so also is the smaller cavity between the lens and the

cornea.

The crystalline lens is convex on both sides, and as pure and transparent as a drop of water, though it is formed of concentric folds or layers, like the coats of an onion. Whoever has seen a camera obscura, knows that a glass lens of similar shape will form and throw upon a screen an image of any object placed before it. This the crystalline lens, owing to its peculiar structure, does with much greater perfection. The eye, then, is just a camera obscura, in which this lens forms the image, and the retina is the screen which receives it. When the rays of light from an external object fall upon the eye, they pass readily through the transparent cornea and the fluid within it. The iris adjusts itself so as to admit the necessary quantity. The light then falls on the crystalline lens, whose construction is so marvellously perfect, that a distinct miniature image of the object looked at, though it may be an extensive landscape, is formed upside down on the retina behind. So far the process is similar to that which takes place in a camera, though neither can be fully explained here. But now a new element is introduced. The optic nerve, connected with the retina, conveys the impression to the brain, and the mind sees, not the inverted image, but the object itself in its true erect position. That there is an inverted image, however, may be proved by taking the eye of an ox, paring off the back part of the sclerotic and choroid coats, and placing the eye in a hole of a shutter, so as to look out on a landscape. If the room be sufficiently dark, the image on the retina may then be seen from behind.

We cannot fail to be struck with wonder at the correctness of these minute pictures, which are ever forming, and ever changing, in our eyes as we look around us. A landscape of several miles in extent is brought into a space whose diameter is only about half an inch, yet the multi

tude of objects which it contains are all preserved, all discriminated in their magnitudes, positions, figures, and colours. With good reason was it said by a distinguished philosopher, that the examination of the eye is a cure for atheism. If anything can abate our admiration of the smallness of the visual tablet compared with the extent of vision, it is a reflection which the study of nature constantly forces upon us, that, in the hands of the Creator, great and little are nothing. "One day," an apostle tells us (2 Pet. iii. 8), " is with the Lord as a thousand years;" and we are fully warranted in adding, one inch is as a thousand miles. Time and space vanish in presence of Infinity.

QUESTIONS FOR EXAMINATION.

What are the functions of the nervous system? Of what substance is it composed? What parts of the body form the great nervous centre? Describe the structure of the brain. How many nerves proceed from within the skull? How many from the brain? from the spinal cord? What is peculiar about the roots of the spinal nerves? In what part of the body is the mind supposed to reside? Explain the process of voluntary motion. Give instances of involuntary motion. Where is the seat of sensation? What is the use of the organs of the senses? How large is a man's eye? Describe its structure. What is the use of the iris, the crystalline lens, and the retina? To what optical instrument is the eye similar? How may it be demonstrated that an image is formed at the back of the eye? In what respects is this image wonderful?

THE ISLAND.

Ir the author of the "Irish Melodies" had ever had a little isle so much his own as I have possessed, he might not have found it so sweet as the song anticipates. It has been my fortune, like Robinson Crusoe, to be thrown on such a desolate spot; and I felt so lonely, though I had a follower, that I wish Moore had been there. I had the honour of being in that tremendous action off Finisterre, which proved the end of the earth to many a brave fellow. I was ordered with a boarding party forcibly to enter the Santissima Trinadada; but in the act of climbing into the quartergallery, which, however, gave no quarter, was rebutted by the butt-end of a gun-a marine's, who remained the quarter

master of the place. I fell senseless into the sea, and should no doubt have perished in the waters of oblivion, but for the kindness of John Monday, who picked me up to go adrift with him in one of the ship's boats. All our oars were carried away-that is to say, we did not carry away any oars; and while shot was raining, our feeble hailing was unheeded. As may be supposed, our boat was anything but the jollyboat, for we had no provisions to spare in the middle of an immense waste. We were, in fact, adrift in the cutter, with nothing to cut. We had not even junk for junketing, and nothing but salt water, even if the wind should blow fresh. Famine, indeed, seemed to stare each of us in the face—that is, we stared at one another. We were truly in a disagreeable pickle, with oceans of brine and no beef; and I fancy we would have exchanged a pound of gold for a pound of flesh. No bread rose in the east, and in the opposite point we were equally disappointed. We could not compass a meal any how, but got meally-mouthed, notwithstanding.

Time hung heavy on our hands, for our past days seemed to pass very slowly; and our strength was rapidly sinking, from being so much afloat. Still we nourished Hope, though we had nothing to give her. But at last we lost all prospect of land, if one may say so when no land was in sight. The weather got thicker as we were getting thinner; and though we kept a sharp watch, it was a very bad look-out. We could see nothing before us but nothing to eat and drink. At last the fog cleared off, and we saw something like land right a-head; but, alas! the wind was in our teeth as well as in our stomachs. We could do nothing but "keep her near;" and as we could not keep ourselves full, we luckily suited the course of the boat, so that, after a tedious beating about-for the wind not only gives blows, but takes a great deal of beating—we came to an island. Here we landed, and our first impulse on coming to dry land was to drink. There was a little brook at hand to which we applied ourselves till it seemed actually to murmur at our inordinate thirst. Our next care was to look for some food; for though our hearts

were full at our escape, the neighbouring region was dreadfully empty. We succeeded in getting some natives out of their bed, but with difficulty got them open: a common oyster-knife would have been worth the price of a sceptre. Our next concern was to look out for a lodging, and at last we discovered an empty cave, reminding me of an old inscription at Portsmouth, "The hole of this place to let." We took the precaution of rolling some great stones to the entrance, for fear of last lodgers-lest some bear might come home from business, or a tiger to tea. Here, under the rock, we slept without rocking; and when, through the night's failing, the day broke, we saw, with the first instalment of light, that we were upon a small desert isle, now for the first time an Isle of Man.

HOOD.

THE BROOK.

[ALFRED TENNYSON was born in 1810, and was made Poet Laureate when Wordsworth died in 1850. He first published three successive volumes of miscellaneous poems, and then, latterly, the "Princess," "In Memoriam," "Maud;" and in 1859 appeared "Idylls of the King, or Romances of the Court of King Arthur." He is generally and justly esteemed the truest poet of the day; though his intellectual style of thought and feeling, and his artistic subtlety of composition, not to speak of forced conceit, vague conception, and occasional prolixity, necessarily circumscribe the circle of his readers. He can never be a popular poet: no poet of the highest order could have written his most celebrated work, "In Memoriam," a lament for a college friend (Arthur H. Hallam, the son of Hallam the historian). He sometimes leaps into the heart of a grand subject, as in the "Charge of the Light Brigade," and throughout his compositions there runs a delightful verbal melody, now bursting forth into high dramatic power, now sweetening into some beautiful lyric strain. Careful to fastidiousness in composition, he has yet, in a small compass, given us an unequalled variety of character and theme, and mingling through all we have ever and anon happy glimpses of old England, its scenery, and its life.]

I come from haunts of coot and hern,

I make a sudden sally,

And sparkle out among the fern,

To bicker down a valley.

By thirty hills I hurry down,
Or slip between the ridges,
By twenty thorps, a little town,
And half a hundred bridges.

Till last by Philip's farm I flow
To join the brimming river;

For men may come, and men may go,
But I go on for ever.

I chatter over stony ways,
In little sharps and trebles,
I bubble into eddying bays,
I babble on the pebbles.

With many a curve my banks I fret,
By many a field and fallow,
And many a fairy foreland set
With willow-weed and mallow.

I chatter, chatter, as I flow

To join the brimming river;

For men may come, and men may go,
But I go on for ever.

I wind about, and in and out,
With here a blossom sailing,

And here and there a lusty trout,
And here and there a grayling,

And here and there a foamy flake
Upon me, as I travel,

With many a silvery waterbreak
Above the golden gravel,

And draw them all along, and flow

To join the brimming river;

For men may come, and men may go,

But I go on for ever.

TENNYSON.