Note 3 — INTRODUCTION.

A writer of the last century remarks, that "he cannot possibly admit the sun to possess the least manner of heat, but rather to contain the capabilities of fire, like a stick, or a flint, though with a faculty of expressing it, by its own action, which the others have not. I imagine its beams not to be hot, in their rectilineal direction, but productive of this effect, from reflection, only. If the rays of the sun were fire, in the first instance, those consequences would naturally follow, that our friend and correspondent Tria so well describes in his Day of Judgment, 'The rivers were dried up, and liquid ore supplied their burning channels. The clouds were turned to fire, and shot through the astonished sky. The air was flame, and breathing was no more. The firmament was melted down, and rained its sulphur o'er the prostrate globe, &c.' The sun emanates light only, in the direct line, but owes its heat to reflection. We feel it, therefore, more intensely, in a valley, than on a hill. Why are the Alps and Pyrennees crowned with eternal frosts, while the shepherds, with their flocks, are sheltering their scorching heads from the heat of the sun, at the foot of them? Why do the upper regions of the air shower down their hail and snow, to be thawed and melted here below? Why shall a lens of ice receive the rays above, so coldly, and transmit them so intensely hot, beneath? Why is it warmer, in summer, though the sun is farther off, than in winter, when 'tis so much nearer to us? Because of our situation, in regard to it, only. In the first case the rays are vertical, in others lateral; and perpendicular reflections are stronger, than oblique ones. We judge of fire above, from what we feel below, &c."

The summit of Ætna, notwithstanding the fire of the volcano, is covered almost all the year with snow. Fazello, speaking of this says, that "this region extends nearly twelve miles; and, even in summer, is almost perpetually covered with snow, and extremely cold: which is the more wonderful as the summit continually produces, nourishes, and pours forth flames amid the ice and snow with which it is enveloped." Solinus says, "Ætna, in a wonderful manner, exhibits snows mixed with fires; and retains every appearance of the severest winter, amid her vast conflagrations."

Silius Italicus, and Claudian, and Pindar, who lived 500 years before the Christian era, bear testimony to the antiquity of this fact.

Silius Italicus, from the Latin.

Claudian, from the Latin.

Pindar, from the Greek.

The height of Ætna is generally estimated at 11,000 feet above the sea. In 1755, it issued out a torrent, not of mud, as was supposed, but of snow and ice melted by the lava. The same thing happened at the volcano of Cargarossa in South America.

The celebrated Herschel, (Phil. Trans. 1801, and Nich. Jour. 1. 13), in considering the construction of the sun, infers it to be a habitable globe more magnificent than our earth, or other planets, and that its lucid substance is not a liquid nor an elastic fluid; but that it exists in the manner of luminous clouds, swimming in the transparent atmosphere of the sun, or rather of lucid decompositions taking place within that atmosphere. The Philosophical Transactions, 1795, p. 72, also contains remarks on this lucid matter. Having rejected the old terms of spots, nuclei, penumbræ, and luculi, he has substituted those of openings, shallows, ridges, nodules, corrugations, indentations, and pores. The openings are places where the luminous solar clouds are removed, which he thinks are produced by a wind or gas from the sun's body. Shallows are depressions below the luminous clouds, and are caused by the propelling gas, which produces the openings. They are tufted like masses of clouds. Ridges are elevations of the luminous clouds. The length of one of the longest was found to be 75,000 miles. They generally surround the openings. Herschel thinks it probable, from appearances, that the luminous matter is disturbed at top by the transparent elastic fluid, which issues from the openings. Nodules are small elevations of the luminous matter. Corrugations are smaller elevations and depressions of the same matter. Indentations are the dark places of corrugations. That they are not much depressed, is deduced from their visibility near the margin of the sun. They are of the same nature as shallows, and of different sizes. Pores are the low places of indentations. The doctor is of opinion, that the phenomena before described could not appear, if the shining matter were a liquid; because, by the laws of hydrostatics, the openings, shallows, indentations, and pores would be filled up. Still less could these phenomena exist with the supposition of elastic fluidity. The shining matter, he concludes, must exist in the manner of empyreal luminous or phosphoric clouds. The planetary atmosphere of the sun, its great height, its density, as inferred from the power of gravitation, which is known to be twenty-seven times stronger at the sun's surface than with us, and other subjects are also discussed. He supposes the gas to pass from the sun itself upwards to the region of the clouds, so as to generate pores, corrugations, &c. He concludes finally, that if this view of the solar appearances be well founded, there will be no difficulty in ascertaining the actual state of the sun with regard to its energy in giving heat and light.

In a paper on the "Construction of the Heavens," the doctor thinks it probable, that the great stratum called the milky way is that in which the sun is placed, though perhaps not in the centre of its thickness. The celebrated astronomer Lalande supposes the spots before mentioned to be parts of the solid body of the sun, but admits not a luminous atmosphere, but a luminous ocean. For the observations of Dr. Young, see his Natural Philosophy, and of sir Isaac Newton, his Principia, &c. Consult also Biot.

Sir Isaac Newton has asserted, according to Nicholson, (British Encyclopedia) "that the density of the sun's heat, which is proportioned to his light, is seven times as great in Mercury as with us, and that water there would be all carried off in the shape of steam, for, he found, by experiments with the thermometer, that a heat seven times greater than that of the sun's beams in summer will serve to make water boil." That fixed stars are of the same nature as the sun, since they agree with it in several particulars, as in the property of emitting light continually, and in retaining constantly their relative situation with but little variation, is generally admitted. They are supposed also to emit heat as well as light. The sun is, therefore, considered a fixed star comparatively near us, and the fixed stars, which seem as centres to other systems of worlds, as suns at immense distances from us. Taking the distance of the sun from us to be, as is found by calculation, 95,000,000 miles, we may infer, that every thing must be scorched up at its surface; but this question is put at rest, if we consider that the sun's rays act on a calorific medium, as the cause of changing quiescent into distributable heat. May not light itself, by some process unknown to us, produce calorific rays? That heat and light are both material, and possess some properties in common, that for instance, of reflection and refraction, are facts well known; but to account for the peculiar agency of light, if it be admitted, is a problem, which, perhaps, will never be settled?