In northern latitudes the effects of atmospheric reflection and refraction are very familiar to the natives. By the term of uphillanger the Icelanders denote the elevation of distant objects, which is regarded as a presage of fine weather. Not only is there an increase in the vertical dimensions of the objects affected, so that low coasts frequently assume a bold and precipitous outline, the objects sunk below the horizon are brought into view, with their natural position changed and distorted. In 1818, Captain Scoresby relates that, when in the polar sea, his ship had been separated for some time from that of his father, which he had been looking out for with great anxiety. At length, one evening, to his astonishment, he beheld the vessel suspended in the air in an inverted position, with the most distinct and perfect representation. Sailing in the direction of this visionary appearance, he met with the real ship by this indication. It was found that the vessel had been thirty miles distant, and seventeen beyond the horizon, when her spectrum was thus elevated into the air by this extraordinary refraction. Sometimes two images of a vessel are seen, the one erect and the other inverted, with their topmasts or their hulls meeting, according as the inverted image is above or below the other. Dr. Wollaston has shown that the production of these images is owing to the refraction of the rays through media of different densities. Looking along a red-hot poker at a distant object, two images of it were seen, one erect and the other inverted, arising from the change produced by the heat in the density of the air. A singular instance of lateral mirage was noticed upon the Lake of Geneva by MM. Jurine and Soret, in the year 1818. A bark near Bellerire was seen approaching to the city by the left bank of the lake; and at the same time an image of the sails was observed above the water, which, instead of following the direction of the bark, separated from it, and appeared approaching by the right bank—the image moving from east to west, and the bark from north to south. When the image separated from the vessel, it was of the same dimensions as the bark; but it diminished as it receded from it, so as to be reduced to one-half when the appearance ceased. This was a striking example of refraction, operating in a lateral as well as a vertical direction.
Ignis Fatuus. This wandering meteor known to the vulgar as the Will-o’-the-Wisp, has given rise to considerable speculation and controversy. Burying-grounds, fields of battle, low meadows, valleys, and marshes, are its ordinary haunts. By some eminent naturalists, particularly Willoughby and Ray, it has been maintained to be only the shining of a great number of the male glow-worms in England, and the pyraustæ in Italy, flying together—an opinion to which Mr. Kirby, the entomologist, inclines. The luminosities observed in several cases may have been due to this cause, but the true meteor of the marshes cannot thus be explained. The following instance is abridged from the Entomological Magazine:—“Two travelers proceeding across the moors between Hexham and Alston, were startled, about ten o’clock at night, by the sudden appearance of a light close to the road-side, about the size of the hand, and of a well-defined oval form. The place was very wet, and the peat-moss had been dug out, leaving what are locally termed ‘peat-pots,’ which soon fill with water, nourishing a number of confervæ, and the various species of sphagnum, which are converted into peat. During the process of decomposition these places give out large quantities of gas. The light was about three feet from the ground, hovering over the peat-pots, and it moved nearly parallel with the road for about fifty yards, when it vanished, probably from the failure of the gas. The manner in which it disappeared was similar to that of a candle being blown out.” We have the best account of it from Mr. Blesson, who examined it abroad with great care and diligence.
Ignis Fatuus.
“The first time,” he states, “I saw the ignis fatuus was in a valley in the forest of Gorbitz, in the New Mark. This valley cuts deeply in compact loam, and is marshy on its lower part. The water of the marsh is ferruginous, and covered with an iridescent crust. During the day bubbles of air were seen rising from it, and in the night blue flames were observed shooting from and playing over its surface. As I suspected that there was some connection between these flames and the bubbles of air, I marked during the day-time the place where the latter rose up most abundantly, and repaired thither during the night; to my great joy I actually observed bluish-purple flames, and did not hesitate to approach them. On reaching the spot they retired, and I pursued them in vain; all attempts to examine them closely were ineffectual. Some days of very rainy weather prevented further investigation, but afforded leisure for reflecting on their nature. I conjectured that the motion of the air, on my approaching the spot, forced forward the burning gas, and remarked that the flame burned darker when it was blown aside; hence I concluded that a continuous thin stream of inflammable air was formed by these bubbles, which, once inflamed, continued to burn, but which, owing to the paleness of the light of the flame, could not be observed during the day.”
The ignis fatuus of the church-yard and the battle-field arise from the phosphuretted hydrogen emitted by animal matter in a state of putrefaction, which always inflames upon contact with the oxygen of the atmosphere; and the flickering meteor of the marsh may be referred to the carburetted hydrogen, formed by the decomposition of vegetable matter in stagnant water, ignited by a discharge of the electric fluid.
CAMPAIGNING STORIES.
NO. II.—THE CAPTIVE RIVALS.[[1]]
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