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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 ; wbich 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 IU.

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

See Pbilos. Trans. No. 482.-Orig. + No. 482, No. 442.-Orig.

high. After great rains and snows, they said, the whole bare patch. of about nive 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.

[Phil. Trans. 1750.

SECTION IV.

1. Fiery Exhalations or Damp, that set on Fire rarious 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 bay, and two barns, one full of corn, the other of hay. I call it on. 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 Merionethe shire, 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 Subday; but that now of late it appears sometbing 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 ; is, 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 uninflammable 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 MOC.. MOONS; GLORIES; REFRACTION OF ICELAND CRYSTAL.

SECTION I.

Explanation of the principle of Atmuspheric Deceplions. All these curious and interesting phænomena 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. v. 144, in which the poet enters upon a description of the mirage (or glamer as it is called in the Highlands) å 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 couvtries, 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, bow. 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.

phænomena, Diodorus Siculus makes particular mention in the fiftieth section of his third book, and points out the regions of Africa situate between the Syrtes and Cyrene, as the theatre of their most extraordinary appearance: περι γαρ τινας καιρους, says he, και μαλιστα κατα τας νηνεμιας, συστασεις ορωνται κατα τον αερα, παντοιων ΖΩΩΝ ιδεας εμφαινουσαι· τουτων δ', αι μεν ηρεμουσιν, αι δε κίνησιν λαμβανουσιν και ποτε μεν υποφευγουσι, ποτε δε διωκoυσι. “ Even in the serenest weather, there are sometimes seen in the air certain condensed exhalations, that represent the figures of all kinds of animals; occasionally, they seem to be motionless, and in perfect quietude; and occasionally to be flying; while immediately afterwards, they themselves appear to be the pursuers, and to make other other objects fly before them.” This phenomenon is, in reality, seldom observed, except in serene weather; and it should seem, upon every theory yet offered to account for it, from the ingenious explanation of our own poet to that of M. Monge in the Memoirs relative to Egypt, that such an atmosphere is nearly or altogether necessary to its existence. The illusion has been noticed as frequently by modern as by ancient observers; and M. Crantz, in his History of Greenland, Vol. I. 49. bas given a pic. ture of it, not essentially differing from the above just quoted from Diodorus Siculus. It is not confined to any particular part of the globe, but generally makes its appearance on the coast; the at. mosphere, as I have already observed, being commonly clear ånd tranquil, and the phenomenon usually succeeded by a fall of rain. Our own sailors, from its more general appearance, call it a fog-bank ; by many writers, it is denominated fata Morgana, and by the French, mirage.

For this atmospheric delusion, various causes have been assigned ; and especially by Kircher, Scholt, and Gaspard Monge, who ac. companied Buonaparte in his Egyptian expedition, as one of the French Sçavans, and was a member of the Institute at Cairo : yet no explanation I have hitherto met with, has been given in satisi factory, or at least in popular language.

To illustrate it as clearly as may be, it is necessary, first of all, to call the reader's attention to the variable state of the atmosphere ; which is commonly of an homogenous, or equable tenuity, and consequently suffers the rays of the sun to penetrate it without any obstruction or change; but at times it is irregular, and composed of

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