Dart from the North on pale electric streams, Or give the Sun's phlogistic orb to roll. 130 135 III. Nymphs! your fine forms with steps impaffive mock Earth's vaulted roofs of adamantine rock; Round her still centre tread the burning foil, 140 And glad with genial warmth the incumbent land. 145 "You from deep cauldrons and unmeasur'd caves Blow flaming airs, or pour vitrefcent waves; O'er fhining oceans ray volcanic light, 150 Or hurl innocuous embers to the night. Alarm with comet-blaze. 1. 133. See additional notes, No. IV. Round her ftill centre. 1. 139. Many philosophers have believed that the central parts of the earth confift of a fluid mafs of burning lava, which they have called a fubterraneous fun; and have supposed that it contributes to the production of metals, and to the growth of vegetables. See additional notes, No. VI. Or Sphere on Sphere. 1. 143. See additional notes, No. VII. Hurl innocuous embers. 1. 152. The immediate cause of volcanic eruptions is believed to be owing to the water of the fea, or from lakes or inundations, finding itself a paffage into the fubterraneous fires, which may lie at great depths. This must first produce, by its coldness, a condensation of the vapour there exifting, or a vacuum, and thus occafion parts of the earth's cruft or shell to be forced down by the preffure of the incumbent atmos phere. Afterwards the water being fuddenly raised into steam, produces all the explofive effeAs of earthquakes. And by new acceffions of water, dur◄ While with loud fhouts to Etna Hecla calls, Thus, when of old, as mystic bards prefume, While frowning Loves the threatening falchion wield, IV. Effulgent Maids! you round deciduous day, Treffed with foft beams, your glittering bands array; On Earth's cold bofom, as the Sun retires, Confine with folds of air the lingering fires; 155 160 165 170 175 ing the intervals of the explofions, the repetition of the fhocks is caused. Thefe circumstances were hourly illustrated by the fountains of boiling water in Iceland, in which the furface of the water in the boiling wells funk down low before every new ebullition. Besides these eruptions occafioned by the fteam of water, there feems to be a perpetual effusion of other vapours, more noxious, and (as far as it is yet known) perhaps greatly more expanfile than water from the Volcanos in various parts of the world. As thefe Volcanos are fuppofed to be fpiracula, or breathing holes to the great fubterraneous fires, it is probable that the efcape of elastic vapours from them is the cause that the earthquakes of modern days are of fuch fmall extent compared to thofe of ancient times, of which veftiges remain in every part of the world, and, on this account, may be faid not only to be innocuous, but useful, Confine with folds of air, 1. 176. The air, like all other bad conductors of electricity, is known to be a bad conductor of heat; and thence prevents the heat acquired from the fun's rays by the earth's furface from being fo foon diffipated, in the fame manner as a blanket, which may be confidered PART I. C O'er Eve's pale forms diffuse phosphoric light, And deck with lambent flames the thrine of Night. So, warm'd and kindled by meridian skies, And view'd in darkness with dilated eyes, 180 as a sponge filled with air, prevents the escape of heat from the person wrap ped in it. This feems to be one caufe of the great degree of cold on the tops of mountains, where the rarity of the air is greater, and it therefore becomes a better conductor both of heat and electricity. See note on Barometz, Vol. II. of this work. There is, however, another caufe to which the great coldness of mountains, and of the higher regions of the atmosphere, is more immediately to be ascribed, explained by Dr. Darwin in the Philos. Trans. Vol. LXXVIII. who has there proved, by experiments with the air-gun and air-pump, that when any portion of the atmosphere becomes mechanically expanded, it abforbs heat from the bodies in its vicinity. And as the air which creeps along the plains expands itself, by a part of the preffure being taken off, when it afcends the fides of mountains, it, at the fame time, attracts heat from the fummits of those mountains, or other bodies which happen to be immerfed in it, and thus produces cold. Hence he concludes, that the hot air at the bottom of the Andes becomes temperate by its own rarefaction when it afcends to the city of Quito; and by its further rarefaction becomes cooled to the freezing point when it afcends to the fnowy regions on the fummits of those mountains. To this also he attributes the great degree of cold experienced by the aëronauts in their balloons; and which produces hail in fummer at the height of only two or three miles in the atmosphere. Diffufe phofphoric light. 1. 177. I have often been induced to believe, from obfervation, that the twilight of the evenings is lighter than that of the mornings at the fame distance from noon. Some may afcribe this to the greater height of the atmosphere in the evenings, having been rarefied by the fun during the day; but as its density muft at the fame time be dimi nifhed, its power of refraction would continue the fame. I fhould rather fuppofe that it may be owing to the phosphorescent quality (as it is called) of almost all bodies; that is, when they have been expofed to the fun, they continue to emit light for a confiderable time afterwards. This is generally believed to arife either from fuch bodies giving out the light which they had previously abforbed, or to the continuance of a flow combuftion which the light they had been previously exposed to had excited. See the next note. "Beccari's fhells. 1. 182. Beccari made many curious experiments on the phofphoric light, as it is called, which becomes visible on bodies brought into a dark room, after having been previously exposed to the sunshine. It appears, from these experiments, that almost all inflammable bodies poffefs this quality in a greater or lefs degree; white paper or linen, thus examined, after having been expofed to the funfhine, is luminous to an extraordinary degree. And if a perfon, fhut up in a dark room, puts one of his hands out into the fun's light for a fhort time, and then retracts it, he will be able to fee that hand diftinctly, and not the other. Thefe experiments feem to countenance the idea of light being absorbed, and again emitted from bodies when they are removed into darknefs. But Beccari further pretended, that So to the facred Sun in MEMNON's fane, "You with light Gas the lamps nocturnal feed, 185 190 fome calcareous compofitions, when expofed to red, yellow, or blue lights, through coloured glaffes, would, on their being brought into a dark room, emit coloured lights. This mistaken fact of Beccari's, Mr. Wilfon decidedly refutes; and, among many other curious experiments, discovered, that if oyfter-fhells were thrown into a common fire, and calcined for about half an hour, and then brought to a person who had previously been fome minutes in a dark room, that many of them would exhibit beautiful irifes of prifmatic colours, from whence, probably, arofe Beccari's mistake. Mr. Wilson from hence contends, that these kinds of phosphori do not emit the light they had previously received, but that they are fet on fire by the fun's rays, and continue for fome time a flow combuftion after they are withdrawn from the light. Wilfon's Experiments on Phosphori. Dodfley, 1775. The Bolognian ftone is a selenite, or gypfum, and has been long celebrated for its phosphorescent quality after having been burnt in a fulphurous fire; and expofed, when cold, to the fun's light. It may be thus well imitated: Calcine oyfter-fhells half an hour, pulverize them when cold, and add one third part of flowers of fulphur, prefs them close into a small crucible, and calcine them for an hour or longer, and keep the powder in a phial clofe ftopped. A part of this powder is to be expofed for minute or two to the funbeams, and then brought into a dark room. The calcined Bolognian ftone becomes a calcareous hepar of fulphur; but the calcined fhells, as they contain the animal acid, may also contain some of the phosphorus of Kunkel. In Memnon's fane. 1. 183. See additional notes, No. VIII. The lamps nocturnal. 1. 189. The ignis fatuus, or Jack a lantern, so frequently alluded to by poets, is fuppofed to originate from the inflammable air, or Hydrogene, given up from moraffes; which being of a heavier kind, From its impurity, than that obtained from iron and water, hovers near the furface of the earth, and, uniting with common air, gives out light by its flow ignition. Perhaps such lights have no existence; and the reflection of a ftar on watery ground may have deceived the travellers, who have been faid to be bewildered by them: if the fact was established, it would much contribute to explain the phenomena of northern lights. I have travelled much in the night, in all feafons of the year, and over all kinds of foil, but never faw one of thefe Will o'wifps. Shine round Calendula. 1. 191. See note on Tropæolum in Vol. II. From leaf to leaf conduct the virgin light, 195 200 The dread Gymnotus. 1. 202. The Gymnotus electricus is a native of the river of Surinam, in South-America; those which were brought over to En gland about eight years ago were about three or four feet long, and gave an electric fhock (as I experienced) by putting one finger on the back, near its head, and another of the opposite hand into the water near its tail. In their native country they are faid to exceed twenty feet in length, and kill any man who approaches them in an hostile manner. It is not only to escape its enemies that this furprizing power of the fish is used, but also to take its prey; which it does by benumbing them, and then devouring them before they have time to recover, or by perfectly killing them; for the quantity of the power feemed to be determined by the will or anger of the animal; as it fometimes ftruck a fish twice before it was fufficiently benumbed to be eafily fwallowed. The organs productive of this wonderful accumulation of electric matter have been accurately diffected and described by Mr. J. Hunter. Philof. Tranf. Vol. LXV. And are fo divided by membranes as to compose a very extensive surface, and are fupplied with many pairs of nerves larger than any other nerves of the body: but how fo large a quantity is fo quickly accumulated as to produce fuch amazing effects in a fluid ill adapted for the purpose, is not yet fatisfactorily explained. The Torpedo poffeffes a similar power in a lefs degree, as was fhewn by Mr. Walch, and another fish lately defcribed by Mr. Paterson. Philof. Tranf. Vol. LXXVI. In the conftruction of the Leyden-Phial, (as it is called) which is coated on both fides, it is known, that above one hundred times the quantity of pofitive electricity can be condenfed on every square inch of the coating on one fide, than could have been accumulated on the fame furface if there had been no oppofite coating communicating with the earth; because the negative electricity, or that part of it which caufed its expanfion, is now drawn off through the glafs. It is alfo well known, that the thinner the glass is (which is thus coated on both fides fo as to make a Leyden-Phial, or plate) the more electricity can be condensed on one of its furfaces, till it becomes fo thin as to break, and thence discharge itself. Now, it is poffible that the quantity of electricity condenfible on one fide of a coated phial may increase in some high ratio in respect to the thinness of the glass, fince the power of attraction is known to decrease as the fquares of the diftances, to which this circumftance of electricity feems to bear fome analogy. Hence, if an animal membrane, as thin as the filk-worm fpins its filk, could be fo fituated as to be charged like the Leyden bottle, without bursting, (as such thin glass would be liable to do,) it would be difficult to calculate the immenfe quantity of electric fluid which might be ac cumulated on its furface. No land animals are yet difcovered which poffefs this power, though the air would have been a much better medium for pro |