Abbildungen der Seite

Lucretius found no definite expression in his own language, rather than the nature of wind properly so called. It is an igneous or fiery aura, not indeed in the open act of combustion, but com. posed of the finest and most minute particles of a peculiar species of elementary fire, which, in a more concentrated form, would necessarily become luminous and burning.

“ Gassendi, indeed, contends, that the Epicurean prester is not ao igneous meteor, but a mere vortex of elastic air. But there can be no doubt of his being mistaken; for Lucretius not only employs a term to which fire, in some modification or other, either elementary or combined, is necessarily attached, but refers us, in the opening of the discussion, by way of explanation, to the constituent particles of lightning, which, he expressly declares, con. sist of the very finest and most attenuate fiery atoms.

“ Fiery, too, and of the common essence of lightning is this meteor asserted to be, by the philosophy of the present day. For it is regarded as an electrical phænomenon; as, indeed, is almost every atmospherical meteor, as well as a great variety that are subterraneous. In describing the powers and operation of the thunder-cloud, in note on v. 256 above, I have noticed its wondere ful faculty of attracting, with almost instantaneous speed, the lighter and adscititious clouds in its vicinity, as I have also its submission to the still more strongly attractive power of that part of the earth which lies immediately beneath it, in a state of negative electricity, evidenced by its dipping downwards either in ragged and multiform fragments, or, where the film of the cloud is tenser, in more regular and unbroken protuberances. Retaining then these simple facts in our recollection, it will not be difficult to account for the phænomenon of the prester, or water-spout, upon the principles of the electric theory.

A thunder-cloud, or cloud filled with electric matter, is first uoticed to appear at sea in a sky so serene as to be totally destitute of adscititious clouds, and in an atmosphere so dry, as to be pos. sest of very little and impalpable vapour. Such is the general appearance of the horizon on the commencement of the water-spout. In such a situation, a thunder-storm canoot be the result, for want of the confederate assistance of additional clouds and vapours: but, from the circumstances enumerated above, a very considerable portion of mutual attraction must take place between this isolated cloud, and the portion of the sea immediately beneath it, more especially if the sea be at this time negatively electrified, or destitute of the electric power of which the cloud has a vast surplus. From this mutual attraction, the water directly under the cloud will become protuberant upwards, rising like a hill towards the cloud above, which, in the phænomenon we are now describing, it always does, and the cloud above will become protuberant downwards, elongating itself towards the elevated portion of water beneath. If, in this action of straining, the texture of the cloud be very slight, it will burst into a thousand fragments, and the electric matter contained within it will be quietly dissipated, or attracted to the ocean; but if it be stronger and more viscous, it will continue to stretch without bursting; and, like every other elastic substance, the more it stretches, the narrower will be the projected tube. Such, to the mariner, is the actual appearance of the column of the water-spout, precisely resembling a speaking. trumpet, with its base or broader part uppermost. When the mouth of this projected tube touches the rising hillock of water, if the attraction of the negatively electrified ocean be superior, the electric aura, we may naturally suppose, will be drawn downwards, and the empty cloud be totally dissipated; but, as will generally occur in the case of a positive force applied to a negative, if the attraction of the electric cloud prove victorious, it will continue to suck up the rising hillock of water till it is altogether sated, and can hold no more. At this time the cloud must neces. sarily burst from its own weight and distention, and, in proportion to its size, and the deluge of water and electricity it discharges, will be the mischief produced. It is said, that it may occasionally be rent, at a distance, by making a violent noise, on board the ship in which it is perceived, by files, saws, or other discordant in. struments; and, certainly, whatever will tend to agitate the air, in any considerable degree, affords some prospect of breaking the cloudy film, and thus dispersing the meteor : but the more ordi. nary method of shooting at it from guns of a large calibre, gives a much stronger, and, indeed, almost certain chance of success : for no mechanical power can agitate the surrounding atmosphere by any means so forcibly as the report of a large cannon : and if it be loaded with ball, it will give a double prospect of discharging the contents of this tremendous spectacle."

Upon that part of the description which relates to the mimic prester, Mr. Good observes as follows: “ Lucretius here alludes to meteors of a similar description, but not quite so tremendous in their effect: and is generally supposed to refer to the hurricane, or, as the Greeks termed it, Exvepia ; which is equally an electri. cal phænomenon, and may be regarded as a prester occurring on land, and consequently as an electric cloud filled with elastic air only, or other vapours received from the atmosphere, and not often with water. It is produced in the same manner as the sea. prester, has the same kind of elongated tube reaching towards the negatively electrified portion of the earth by which it is attracted, and is accompanied, previous to its bursting, by a similar tornado of external air. This elongated tube, as well as the substance of the cloud itself, in the time of Shakspeare, was supposed to have its film or fibres condensed and rendered firmer by the operation of the rays of the sun; but there is no necessity for such an idea :

-the dreadful spout Which shipmen do the hurricano call, Constriog'd in mass by the almighty sun.

Troilus and CRESSIDA.

“ We may account for the phenomenon in this manner : that the thirsty cloud, in consequence of a more elevated position than ordinary in the atmosphere, at the time it commences its attraction with the water below, satiates and distends itself, by means of its proboscis, with absorbed air alone, prior to the actual contact of such proboscis with the hillock of rising water; so that, by the time this elongating spout extends to the attracted hillock, it is totally incapable of containing any thing farther."

Cavallo thinks electricity rather a consequence than a cause of water-spouts; and notices that they sometimes vanish and reappear.

Franklin, in his work on electricity, conceives a vacuum is made by the rotatory motion of the ascending air, as when water is run. ning through a tunnel, and that the water of the sea is thus raised. But it is justly observed by Dr. Young, that no such cause as this could do more than produce a slight rarefaction of the air, much less raise the water to above thirty or forty feet. At the same time the

Yol.iii. p. 306.

force of the wind thus excited might carry up much water in de. tached drops, as it is really observed to exist in water-spouts. Dr. Young remarks, moreover, in another passage, that the phenomena of water.spouts, if not of electrical origin, appear to hase some connexion with electrical causes. A water-spout generally consists of large drops, like a dense rain, much agitated, and descending or ascending with a spiral motion, at the same time that the whole spout is carried along horizontally, accompanied in general by a sound like that of the dashing of waves. Spouts are sometimes, although rarely, observed on shore, but generally in the neighbourhood of water. They are commonly largest above; sometimes two cones project, the one from a cloud, the other from the sea below it, to meet each other, the junction being accompanied by a flash of lightoing: and when the whole spout has exhibited a luminous appearance, it has perhaps served to conduct electricity slowly from the clouds to the earth. Some of these circumstances may be explained by consi. dering the spout as a whirlwind, carrying up drops of water, which it has separated from the surface of the waves; and the remainder may perhaps be deduced from the co-operation of electricity, al. ready existing in a neighbouring cloud.



Genuine Presters or Water-spouls.

1. Observed in the Mediterranean.

By Alexander Stuart,

August 27, 1701, being on the coast of Barbary, to the north. ward of the town of Bona, upwards of ten leagues distance at sea, about seven o'clock at night, soon after sunset, there appeared in

the N.E. which was directly up the gulf of Lyons from us, great - and continued flashes of lightning, one after another, with hardly

any intermission, and this, without thunder, it continued till the next morning; the flashes of lightning sometimes representing the sudden appearance of a star, and at other times of a flaming sword, and again of a silver cord stretched along the clouds, or as the irregular rents of a phial from top to bottom. About eight next morn

[graphic][merged small][merged small][merged small]
« ZurückWeiter »