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in the very middle of the winter, when the weather is very cold, and the ground covered with snow, they are observed more fre. quently than in the hottest summer. Nor does either raia or snow n any wise prevent or hinder their appearance; on the contrary, they are more frequently observed, and cast a stronger light, is rainy and wet weather. But since they do not receive any damage from wet weather, and since, on the other hand, it has never been observed, that any thing was set on fire by them, though they must needs in their moving to and fro, meet with a good many combustible substances, it may from thence be inferred, that they have some resemblance to that sort of phosphorus that shines in the dark, without burning any thing. As to the appearance of this phenomenon in mountainous parts, they differ in nothing else but in size ; these latter being never observed any larger than the flame of an ordinary candle. In general, these lights are great friends to brooks and rivers, being frequently observed along their banks ; perhaps because the air carries them thither more easily than any where else. In all other particulars, as in their motion, the manner of their appearance, their disappearing sometimes very suddenly, their light, the height they rise to, and their not being affected either by rainy or cold weather, they are the very same with the cularsi above described, or the large Will with a Wisp, as observed in the plains.

A young gentleman, a very accurate and skilful observer of Da. tural appearances, travelling sometime in March last, between eight and nine in the evening, in a mountainous road, about ten miles south of Bologna, as he approached a certain river, called Rioverde, he perceived a light, which shone very strongly on some stones that lay on the banks. It seemed to be about two feet above the stones, and not far from the water of the river: in figure and size it had the appearance of a parallelopiped, somewhat above a Bolognese foot in length, and about half a foot high, its longest side lying parallel to the horizon : its light was very strong, insomuch that he could very plainly distinguish by it part of a neigh. bouring hedge, and the water in the river. The gentleman's curi. osity tempted him to examine it a little nearer; in order to which, he advanced gently towards the place, but was surprised to find, that insensibly it changed from a bright red to a yellowish, and then to a pale colour, in proportion as he drew nearer; and that when he came to the place itself, it was quite vanished. On this he stepped back, and not only saw it again, but found that the far. ther he went from it, the stronger and brighter it grew; nor could he, on narrowly viewing the place where this fiery appearance was, perceive the least blackness, or smell, or any mark of an actual fire. The same observation was confirmed by another gentleman, who frequently travels that way, and who asserted, that he had seen the very same light five or six different times, in Spring and Autumn, and that he had always observed it in the very same shape and the same place; which seems very difficult to be accounted for. He said further, that once he took particular notice of its coming out of a neighbouring place, and then settling itself into the figure above described.

[Phil. Trans. Abr. 1729.

SECTION II.

Luminous and Inflammable Exhalation on the Snows of the

Appennines.

We have ventured in the first section of this chapter to ascribe the greater number of luminous exhalations that float over the sur. face of the earth to the extrication and inflammation of hydrogen. gas, similar to that which is so frequently elicited in coal mines, under the name of fire-damp. In the midst of the snows on the summit of the Apennines, was traced in the middle of last century, a luminous and burning exhalation which evidently proceeded from this cause. It is clearly and accurately described by Robert More, Esq. in a letter published in the Philosophical Transactions, vol. xlvii.; in which, among other facts of natural history, he observes that the fire among the snows on the summit of the Apen, nines is of the same sort with that about a little well at Brosely* in Shropshire; of which the Society has had an account; the same as of the foul air sent them from Sir James Lowther'st coal pits ; and the like made by a gentleman with filings of iron and oil of vitriol. The flame, when he saw it, was extremely bright, covered a surface of about three yards by two, and rose about four feet high. After great rains and snows, they said, the whole bare patch, of about niue yards diameter, flames. The gravel, out of which it rises, at a very little depth, is quite cold. There are three of these fires in that neighbourhood ; and there was one they call extinct. He went to the place to light it up again, and left it flaming. The middle of the last place is a little hollowed, and had in it a puddle of water: there were strong ebullitions of air through the water; but that the air would not take fire; yet what rose tbrough the wet and cold gravel flamed brightly. Near either of these fiames, removing the surface of the gravel, that below would take fire from lighted matches.

* See Philos. Trans. No. 482.-Orig. † No. 482, No. 442.-Orig.

[Phil. Trans. 1750.

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1. Fiery Exhalations or Damp, that set on Fire various Hay

Ricks in Pembrokeshire.

In a Letter from Mr. Edward Floyd, to Dr. Leister, F.R.S. dated

Jan. 20, 1693-4. I am wholly intent at present on giving you the best account I can of a most dismal and prodigious accident at Hartech in this county (Pembrokeshire), from the 24th to the 30th of December, 1693. It is of the unaccountable firing of sixteen ricks of hay, and two barns, one full of corn, the other of hay. I call it un. accountable, because it is evident they were not burnt by common fire, but by a kindled exhalation, which was often seen to come from the sea, and lasted at least a fortnight or three weeks; and annoyed the country, both by poisoning the grass and firing the hay, for the space of a mile. It was a weak blue flame, easily extinguished, and did not in the least burn any of the men who in. terposed their endeavours to save the hay, though they ventured not only closeto it, but sometimes into it. All the damage sustained happened constantly in the night. There are three small tenements in the same neighbourhood, where the grass is so infected, that it absolutely kills all manner of cattle that feed on it. The grass has been infectious these three years, but not thoroughly fatal till this last,

2. Continuation of the above Account, from the same, to the

same, dated August 23, 1694. An intelligent person*, who lives near Harlech in Merionethshire, assured me the fire still continues there; that it is observed to come from a place called Morva.bychan in Caernarvonshire, about eight or nine miles off, over part of the sea. That cattle of all sorts, as sheep, goats, hogs, cows, and horses, still die apace; and that for certain, any great noise, as winding horns, drums, &c. repels it from any house, or barn, or stacks of hay: on ac. count of which remedy, they have had few or no losses in that kind since Christmas. That it happened during this summer, at least, one night in a week, and that commonly either Saturday or Sunday ; but that now of late it appears something oftener. The place whence it proceeds is both sandy and marshy.

[Phil. Trans. 1693.4. It is not impossible that the winding of horns, drums and other noises here referred to may have been serviceable in destroying the fiame; if, as there can be little doubt, the inflammable material were hydrogen gas; for whatever would tend to change and ventilate the gas, as all loud sounds must necessarily do, would speedily render it weaker, or in other words more freely combined with the upinflammable air of the atmosphere.

[EDITOR.

CHAP. XLVIII.

ON

ATMOSPHERIC DECEPTIONS.-FATA MORGANA, MIRAGES, GLAMER OR LOOMING; HALOS ; MULTIPLIED RAINBOWS; PARHELIONS, AND PARASELENITES, OR MOCK-SUNS, AND MOCE. MOONS; GLORIES; RETRACTION OF ICELAND CRYSTAL,

SECTION I.

Explanation of the principle of Atmospheric Deceptions. All these curious and interesting phænomená proceed from one common cause, irregularity in the tenuity of the atmospheric fluid. To enter however, very fully into their origin and distinctions, would lead us farther into the laws of optics than the nature of the present work would justify. One of the clearest and most concise explanations that has occurred to us, and at the same time most adapted to popular comprehension, is contained in a note to Mr. Good's Translation of Lucretius, book iv. P. 144, in which the poet enters upon a description of the mirage (or glamer as it is called in the Highlands) à distorted and fantastic representation of the scenery before us--a description which we regret that we have not space to copy.

The note is as follows: These monstrous appearances in the atmosphere are not equally common to all couutries, but depend in a great measure upon lo. cal causes and combinations. According to Pliny, the regions of Scythia within Imaus; and, according to Pomponius Mela, those of Mauritania behind mount Atlas, are peculiarly subject to them; and they are generally regarded by the barbarous inhabitants of such countries as spectres, or aerial demons. Of such grotesque

* It might perbaps be expected, before we thus enter upon a new subject, that we should touch upon the phenomenon of Fairy Rings, or Circles; which have from a very high antiquity, been generally ascribed to the effect of lightning, or fiery meteors of some kind or other. More accurate attention, bor. ever, has proved them to be the production of a fungus, the agaricus orcades, and hence to fall within the range of the curiosities of Botany.

[EDITOR

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