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IV.

In some rainbows may be discovered three arches within the purple of the common bow: 1. yellowish green, darker green, purple; 2. green, purple; 3. green, purple. Rainbows, too, are sometimes seen, when the hoar frost is descending.

Aristotle states, that he was the first, who ever saw a lunar rainbow. He assuredly means, that he was the first, who ever described one ;-since lunar rainbows must have been observed in all ages. That it was unknown to St. Ambrose, however, is evident from his belief, that the bow, which God promised Noah, he would place in the firmament, after the Deluge, " as a witness, that he would never drown the world again," was not to be understood of the rainbow, "which can never appear in the night; but some visible virtue of the Deity." Notwithstanding this assertion of St. Ambrose, I have had the good fortune to see several; two of which were, perhaps, the finest

⚫ ever witnessed in any country. The first formed an arch

'First remarked by Dr. Langwith.-Phil. Trans. No. 375.

2 A lunar rainbow was seen by the Portuguese pilot, near the island of St. Thomas, A. D. 1524. "We observed the constellation of Il Crusero," says he," very high from the island of San Thome, and remarked, that the moon, after rain, forms during the night a rainbow, similar to what the sun produces in the day, except that the colours are nebulous." The original of this passage was written many years before Newton was born.-When M. Labillardiere* was in search of La Perouse, he saw a lunar bow on the coast of Africa; in which, as the bow was between the ship and the moon, the colours were inversely from those of the sun. Lunar rainbows are frequent in St. Domingo.

*Vol. i. 62. Also, i. 230.

over the Vale of Usk. The moon hung over the Blorenge; a dark cloud suspended over Myarth; the river murmured over beds of stones; and a bow, illumined by the moon, stretched from one side of the vale to the other. Had Wouvermanns, or Bassano, at that moment, thrown their mantles over me! For then I recalled to recollection that passage in the Chinese mythology, where the mother of Fo-hi, surnamed the flower-loving," is represented as walking in the evening, on the banks of a rivulet, and finding herself suddenly enveloped in a rainbow. She became pregnant, from that moment; and, after a period of twelve years, gave birth to a son, who was honoured with the title of the Star of the Year."

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The second I saw from the castle, overlooking the bay of Carmarthen, forming a regular semicircle over the Towy. It was in a moment of vicissitude; and fancy willingly reverted to that passage of Ecclesiasticus, where the writer describes Simon, shining " as a morning star," and "as a rainbow," on the temple of the Eternal. The sky soon cleared, and presented a midnight scene like that, which Bloomfield has described so admirably.

Low on the utmost bound'ry of the sight,
The rising vapours catch the silver light;
Thence fancy measures, as they parting fly,
Which first will throw its shadow on the eye,
Passing the source of light; and thence away,
Succeeded quick by brighter still than they.
For yet above these wafted clouds are seen
(In a remoter sky, still more serene),
Others detached, in ranges through the air,
Spotless as snow, and countless as they're fair;

Scatter'd immensely wide from east to west,
The beauteous semblance of a flock at rest.
These, to the raptur'd mind, aloud proclaim
Their mighty Shepherd's everlasting name.

Bloomfield's Winter, l. 249.

CHAPTER VI.

WHAT appearances in nature can be more beautiful, and, at the same time, more awful, than the wild, and mysterious, motions and colours of the aurora borealis? Sometimes covering, with inconceivable magnificence, the concave of the whole hemisphere; changing their positions every moment; now resembling vast pyramids; or stretching into innumerable columns; varying their shapes and colours with astonishing rapidity, and with endless caprice. Now vanishing in a moment, leaving the heavens sombre and black; and now returning, with increased splendour, shedding a matchless glory over all the heavens !

With respect to the cause of this phenomenon, many hypotheses have been started by natural philosophers. Not one, however, will stand the test of rigid examination. St. Pierre imagines it probable, that it may be caused by the coruscations of ice, at the polar circles; since vast islands of ice are frequently signified, some time before they appear in the horizon, by the coruscations they emit'.

'Ice-blinks are visible at a considerable distance*; and by their effulgence may be seen in the deepest fog, and in the darkest night. Ships may, there

* Mem. Wernerian Society, vol. ii. 292.

This hypothesis gains some confirmation from the circumstance, which has been observed by travellers in Lapland and Siberia, of the aurora being attended by a hissing and a cracking noise. One insuperable objection, however, among many others, may be opposed to this theory. If the remarkable phenomenon, alluded to, proceeded from the coruscations of ice at the polar circles, it would appear regularly every year; whereas, it is now scarcely ever to be seen'; and, in more ancient times, it was even still more unfrequent. Some have imagined it to proceed from the ice islands themselves, which float at particular seasons of the year, along the Northern and Southern Oceans: grounding their opinions principally, upon Captain Cook's having observed, that the ice islands, at the South Pole, illuminated half the horizon to a considerable height. This hypothesis is even more improbable than the former. It is liable to the same insurmountable objection, as to the unfrequency, with the addition of the utter impossibility of our imagining, that any coruscations, caused by objects so comparatively low as ice islands, should ascend to an altitude of several thousand miles; a height to which, in the opinion of many philosophers, particularly Euler and Mairan, the

fore, easily avoid them. The rushing of two fields of ice against each other produces a sound like that of thunder, or artillery. They seem like two planets coming in contact.

1 The first recorded in England, I believe, is noticed by William of Malmsbury, p. 177. A very remarkable one was seen at Naples, July 13, 1787. Emanuel Maria, who wrote a letter to Abbé Fontana, at Florence, descriptive of this phenomenon, says, the light appeared, for the most part, to be under the clouds.-Vid. Il Mercurio Italico, Ottobre, 1787.

VOL. I.

2 Cook's Voyages, vol. i. p. 267, 4to.

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illuminations of the aurora borealis undoubtedly aspire. To add to the difficulty, it has been observed by several travellers in Iceland, that the northern lights proceed from the east and south-east', as well as from the north. In Greenland generally from the east. In Lapland frequently from the south. In Hudson's Bay it resembles an umbrella, darting streams of light from every part of its periphery. At the equator they are never seen.

II.

Franklin supposed the Aurora to be owing to a vast quantity of electricity accumulated in the atmosphere, and unable to pass off into the earth, on account of the non-conducting substance of ice, with which the land and seas are incrusted in the polar regions. Some have also supposed, that it associated with the magnetic fluid: but Lieutenant Parry, when he was in the Arctic regions, could not perceive, during the continuance of the aurora borealis, that it affected the magnetic3 needle in any degree. It neither altered its

The result of Captain Ross's voyage proves, that it appears in every direction; and not unfrequently at small distances from the earth.-Vid. Voy. of Disc. to Arctic Regions. 4to. Appendix ccxxi.

2 From an account published of the voyages of Lowenorn, Egede, and Rothe*, it would seem as if the aurora is occasionally seen even in the daytime.

3 Professor Hansteen of Christiana believes the earth to have four magnetic poles; and that the moon and the sun have magnetical poles also. He believes the aurora lights to be magnetical currents, flowing from one magnetical pole to another immediately opposite: and that they have a form of a

* Vid. Barrow's Polar Regions, p. 332.

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