and magnify the appearance of objects like a lens. The bending or refracting of rays is a cause of many interesting phenomena

in nature.

When we look at a fish at the bottom of a clear pool of water, it seems to lie at a point straight from the eye; but it does not. It is lying at a point nearer to us than it seems. The appearance of it comes up through the water in a straight line, and then, on entering the air, which is a medium of a different density, it makes a turn at an angle towards the eye, as if it came round a sharp corner. Suppose we were to shoot an arrow directly pointed at the fish, we should inevitably hit a spot beyond it. To prove that this is the case, put a stick partly into the water, when the part beneath the surface will seem bent from a straight line; or perform the following experiment:

THE BASIN AND THE SHILLING.

Place a small basin on the table, and lay in it a shilling, in

Fig. 4.

such a situation that, on retiring backwards, we just lose sight of the farther edge of the coin. Now pour water gently into the basin, and as you pour, the shilling, without being moved, will come into sight. As represented in the annexed cut, fig. 4, the ray from the shilling is bent from

its course in coming out of the water towards the eye, and the vision seems to travel by the straight dotted line from the farther or imaginary coin. Here it is clearly proved, that by refraction we can see round the corner of an opaque object.

THE DRINKING-GLASS.

The principle of magnifying, along with a refraction, may be amusingly illustrated as follows:-Take a tall drinking-glass of a conical figure-that is, small at bottom and wide at top-put into the glass a shilling, and fill the glass about half full of water; next place a plate on the top of it, and turn it quickly over, one hand on the glass, and the other on the plate, so that no water may get out. In the glass, which is now turned upside down, we see at the bottom, on the plate, a coin the size of a halfcrown; and somewhat higher up, another piece the size of a shilling.

This phenomenon arises from seeing the piece through the rounded surface of the water at the side of the glass, and through the flat surface at the top of the water at the same time. The rounded surface of a glass or bottle of water, as formerly stated,

magnifies like a lens, and hence the shilling appears magnified to a half-crown. As seen through the top of the water, the rays towards the eye are refracted, as in the previous case of the basin, and the shilling appears in its proper size, but lifted up seemingly out of its place. Having amused yourself with this remarkable phenomenon, you may give the glass and plate to a servant, and desire her to throw out the water, and take care of the two pieces of money. Her surprise will probably be considerable when she finds that the half-crown has disappeared, and that a shilling only remains.

REFRACTION IN AIR.

If we look through a stratum of air of ordinary density, and a stratum a certain degree thinner or thicker, a result precisely similar to looking through air and water will follow. Thus, any stream of heated or thin air, or stream of damp and comparatively thicker air, coming between us and an object, will refract the rays, and our line of vision will be bent. This may be easily proved. Heat a poker to a red-heat in the fire, then hold it up before you, so as to warm and rarefy the air which is in contact with it. Now look close along the poker at an object ten or twelve feet distant, and it will be seen out of the situation it actually occupies; and not only so, but it will seem to be inverted, or turned upside down. At a distance of more than three-eighths of an inch, the image of the object will appear erect.

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If these explanations be understood, many most interesting, and, to the ignorant, mysterious phenomena in nature will appear simple. When we see the body of the sun or the moon more than usually large, we know that the phenomenon arises from our looking through a moist atmosphere, which, by refraction, acts the part of a magnifying glass. By the same property of refraction the heavenly bodies are never seen in the spot they actually are. The true position of the sun is less or more deceptive, according to the condition of the atmosphere. It is particularly so in the morning and evening. In the morning, when his earliest rays reach our eyes, they have penetrated through a stratum of dense air, and being therefore bent to meet our vision, we actually see the body of the sun before he is above the horizon-like the shilling in the basin, we see him round a corner. In proportion as the sun approaches the zenith, the refraction diminishes, and as he sinks towards evening, it increases. So considerable is it in the hazy atmosphere of the evening, that we retain a sight of the sun's disc after it has sunk. The same phenomena occur in relation to the other heavenly luminaries.

We hope it is now fully understood that the direction of our vision is at all times liable to be disturbed by atmospheric conditions. It may be repeated—as long as the atmosphere betwixt

our person and the object we are looking at is of the same density, we may be said to see in a straight line before us. But if by any cause a portion of that atmosphere is rendered less or more dense, the line of vision is at once bent from its course. thorough comprehension of this simple truth in science has banished a mass of superstition.

FIGURES IN THE AIR.

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In old times, when any unusual phenomenon was considered ominous of disaster, people were thrown into consternation by observing what they believed to be figures in the air. In the west of Scotland, where religious persecution had helped to render the popular mind nervish and suspicious, appearances of this nature gave cause to much needless alarm. In a work now very rare, entitled "An Alarm to a Secure Generation," by John Howie, of Lochgoin, published in 1780, an account is given of certain extraordinary appearances or "visions" seen during the preceding forty years in the moorland districts of Ayrshire and Renfrewshire. We extract the following "declarations" respecting these aerial visitants, for the purpose of showing how easily our ignorant and pious ancestors were discomposed by natural phenomena :—

"John Clark in Croilburn, aged eighty-three years, but fresh in judgment, and ripe of memory, declares that he has seen these visionary appearances several times; but that the following was the most particular: That a good while ago, about the beginning of harvest, on a clear morning about sunrising, as he and his brother went out to gather their flocks, when a little above the house, to their surprise they beheld the appearance of a large body of men, of a dark-bluish colour, standing all in a straight line upon a rising ground. On their left hand, opposite to the rising sun, as they looked upon them with some admiration, they suddenly broke rank, and went off all in detached parties; and marching with great swiftness for some considerable length down a piece of moor ground, until they arrived at a little height, where they were immediately drawn up in a body, and from whence they plainly perceived the appearance of smoke arising to some considerable height above their heads. At last they wheeled to the north, falling in upon a water-side, and then marched up again in parties towards him and his brother (who were now advancing towards the said water-side), until they came within a little distance from them; where, upon a little holm on the water-side, they were immediately drawn up in two parties, and fronted each other, until they came, seemingly, within reach of bayonet; and then made a push with somewhat seemingly across their arms, with such agility, that, as if it had been in a moment, the one party dropt all down to the ground, and the other disappeared: and the said John was so convinced of the reality of what he saw, that he went unto the said piece

of ground where he thought they fell; but there he found nothing. He declares further, that one time he saw them standing in a large body in a clear afternoon, and snow on the ground, and that they shifted ground from one place to another. At another time he saw a party of them standing on a little rising ground, in the evening; and being betwixt him and the wind, he apprehended he felt a breeze of hot wind come in his face from that quarter, which made him a little timid, until he recollected himself: and so he returned home and left them on the place."

A Mr John Howie of Lochend, and a John Boyd, "elder in Collorie," also depone to their having seen the same or similar appearances, which by the credulous collector of these wonderful narratives were considered as having been prognosticatory of the rebellion of 1745, and the war between France and Spain two years later. Modern science, however, informs us that the visions were nothing more than the repeated images of soldiers at drill, also other objects, placed out of the direct view of the spectators-the whole aided, no doubt, by imagination and a wish to tell what was marvellous. It will be observed that the visions were always seen either in the morning or the evening, a time when the refractive power of the atmosphere is greatest.

Many similar stories are related of spectral figures being seen in the mountainous country in the north of England; but these we pass over, to notice a phenomenon which was witnessed a few years ago on Agar, one of the Mendip hills in Wiltshire. It was first observed about five o'clock in the evening, and represented an immense body of troops, mounted and fully accoutred, moving onwards with drawn swords. Their pace and arrangement frequently varied; and the illusion was so complete, that even the bridles could be distinguished, while the horses' feet were seen to move in a perfectly natural manner. The astonished and somewhat terrified cottagers observed the phenomenon for upwards of an hour. These figures, as was afterwards ascer tained, were images of a body of yeomanry who were practising about fifteen miles off, and who were seen over the intervening ground, just as the shilling is seen over the edge of the basin, in consequence of the strata of air at the earth's surface being more dense than the superincumbent strata.

FATA MORGANA.

Analogous to the above mentioned figures, and scarcely less wonderful, is the appearance denominated Fata Morgana, not unfrequently witnessed in the Straits of Messina. At the time of sunrise, on a clear calm day, when the surface of the water is unruffled, a spectator placed on an eminence in the city, with his back to the east, sees towers, churches, and magnificent palaces, with their rows of columns and elaborate ornaments, bodies of men and women, troops in military array, and herds of

cattle feeding in sequestered valleys, pass rapidly along the placid surface of the waters. If the air be much loaded with moisture, the figures are also beheld suspended at some height above the surface. Far from being alarmed at the appearance, the inhabitants seem to consider it a signal of good luck, and rush down to the shore, exclaiming, with joyous accents, “Morgana! Morgana!”

Similar phenomena have been at various times noticed on the shores of England and Ireland, and were formerly attributed by the ignorant peasantry to enchantment, or the fairies. They have likewise been observed at sea; and though well known under the name of fog-banks, yet has their appearance been so imposing as to elude the nicest scrutiny, and to promise refreshment and repose to the fatigued and sea-worn mariner, which a nearer approach is destined to disappoint. In truth, such is the variety of wonders produced in this manner, that to describe them all within ordinary limits would be impossible; we shall therefore content ourselves with mentioning a few of the most remarkable only. The cliffs on the coast of France are fifty miles distant from Hastings in Sussex, and are completely hidden from view by the convexity of the earth's surface; yet, on one particular occasion, the whole line of coast from Calais to Dieppe became distinctly visible to the spectators at Hastings; indeed so clear and perfect was the view thus obtained, that the fishermen could distinguish the places which they had been accustomed to visit, and, with the help of a telescope, could recognise the French boats lying at anchor. The different colours of the land on the heights, and the various buildings, were also perfectly discernible. This remarkable appearance

continued for more than three hours.

SPECTRE OF THE BROCKEN.

Sometimes aërial figures or spectres appear, of vast size, on the top of a hill opposite to the rising sun. The Brocken, the loftiest of the Hartz mountains, a picturesque range lying in the kingdom of Hanover, has long been celebrated on account of an aerial spectral appearance of a gigantic size. This remarkable phenomenon has been witnessed by many travellers, but the best account of it is given by M. Haüy. After having ascended the mountain as many as thirty times, he was at length fortunate enough to witness the interesting spectacle. We subjoin the account of it in his own words :-"The sun rose about four o'clock, and the atmosphere being quite serene towards the east, his rays could pass, without any obstruction, over the Heiwrichshöhe. In the south-west, however, towards Achtermaunshöhe, a brisk west wind carried before it thin transparent vapours, which were not yet condensed into thick heavy clouds. About a quarter past four I went towards the inn, and looked round to see whether the atmosphere would permit me to have