an eagle, was unable to discover it'. Indeed, he did not attempt to assign the cause; it not being his intention to engage himself in framing hypotheses, but to explain the phenomena by experiments only, and to raise his noble superstructure on them. And, therefore, although the facts themselves, and the final causes, are evident, I will not presume to say, how it can come to pass, that bodies act at such immense distances from one another; but would rather acquiesce in adoring the wisdom and power of the great Author of all things, who has inspirited the materials of which the universe consists with such an active quality, as not only serves to preserve the planets themselves entire, but to enable them to revolve about That there is, however, such a principle, is not to be doubted. To deny its existence, would be to deny the truth of facts, established by experiment and demonstration. That two distant bodies will approach toward each other, without any visible agent, either attracting or impelling them, may be made manifest by various instances. The loadstone and a piece of iron mutually attract each other two cork balls, swimming in water, approach together, and meet; and in electricity, we have numberless experiments to show, that several other bodies have the like propensity to unite and adhere to each other. These bodies, it is true, act by particular laws, different from that of gravity; but they serve sufficiently well to illustrate the nature of that principle. Bonnycastle's Introduction to Astronomy, page 119. These principles I consider, not as occult qualities supposed to result from the specific forms of things, but a general law of nature, by which the things themselves are formed; their truth appearing to us by phenomena, though their causes be not yet discovered. For these are manifest qualities, and their causes only are occult, &c.—Newt. Opt. p. 374. Besides the beneficial effects of gravity, in causing, by the lunar influence, the diurnal variations of the tides, we shall find, in another respect, how much this great law of nature is subservient to the good, and even to the very existence, of our globe and all the planets; and that is, in the preservation of their integrity against the effects of their diurnal revolutions. For, without such a band as their luminous centres, in orbits at once the most convenient, invariable, and permanent. O Sun! Soul of surrounding worlds! in whom best seen Shines out THY MAKER 'Tis by thy secret, strong attractive force, As with a chain indissoluble bound, Thy system rolls entire; from the far bourne 6 THOMSON. gravity to keep their parts entire, the whirling about of those globes would shatter them to pieces, and scatter them into the circumambient space. Thus (says Dr. Derham) must it needs befal our own globe, which whirls about at the rate of above 1000 miles an hour, and is composed of earth and water, materials of much too loose a texture to prevent the dissipation, which the centrifugal force of such a rotation must necessarily occasion about the equatorial parts: a rotation that would as easily throw off the parts of the earth, especially the waters, as the whirling round of a wheel or a globe would the loose dust and water lodged thereon. But by reason the gravitating power exceeds the centrifugal, as 2174 exceeds 7,54064, that is, above 288 times; therefore all parts lie quiet and secure in their respective places, and enjoy all the benefits which accompany this motion, without any disturbance from it.' Astro-Theology, b. vi. ch. 2.—He adds, that this is far more remarkable in the Sun, which revolves round its axis, at the rate of 4262 miles an hour; and of Jupiter, which, at its equator, revolves round at the hourly rate of 38,159 miles. Gravity, or the weight of bodies, is not any accidental effect of motion, or of any very subtile matter, but an original and general law of all matter, impressed upon it by God, and maintained in it perpetually by some efficient power, which penetrates the solid substance of it; for gravity never is in proportion to the superficies of bodies, or of any corpuscles, but always to the solid quantity of them. Wherefore we ought no more to inquire how bodies gravitate, than how bodies began first to be moved.-Dr. Clarke's Notes on Rohault, part ii. ch. 28. 2 The Georgian planet being then unknown. No. XII. ON THE CLOUDS; Including the Theory of Evaporation. 'Who can number the clouds in wisdom? JOB. Ye mists and exhalations that now rise MILTON. THE radiant orbs which adorn the night are not the only objects above to attract the philosophic eye. The firmament exhibits inexhaustible subjects of contemplation in a vast variety of igneous, aërial, and aqueous meteors. The latter, which are composed of vapours, or watery particles variously separated and condensed by heat and cold, form the clouds, with all the phenomena of rainbows, hail, snow, rain, dew, &c.' The beautiful, and very often fantastic, appearances of the clouds, have not escaped the observation of the poets: Sometime, we see a cloud that's dragonish ; A vapour, sometime, like a bear or lion, A forked mountain, a blue promontory The igneous or fiery meteors are lightning, aurora borealis, ignis fatuus, draco volans, falling stars, and other fiery phenomena; an account of which will be given hereafter. The aerial or airy meteors consist of flatulent and spirituous exhalations; such as winds, whirlwinds, and hurricanes; for an account of which see No. II. With trees upon 't that nod unto the world, That which is now a horse, even with a thought SHAKSPEARE. When first the sun too powerful beams displays, The sun has lost his rage; his downward orb РОРЕ. Lights up the clouds, those beauteous robes of heaven, THOMSON. At the Tropics, the clouds roll themselves into enormous masses, as white as snow, turning their borders into the forms of hills, piling themselves upon each other, and exhibiting the shapes of mountains, caverns, and rocks. There, as we collect from St. Pierre', may be perceived, amid endless ridges, a multitude of valleys, whose openings are distinguished by shades of purple and vermillion. These celestial valleys exhibit, in their various colours, matchless tints of white, melting into shades of different colours. Here and there may be observed torrents of light, issuing from the dark sides of the mountains, and pouring their streams, like ingots of gold and silver, over rocks of coral. These appearances are not more to be admired for their beauty, than for their endless combinations, since they vary every instant. What, a moment before, was luminous, becomes coloured; what was coloured mingles into shade; forming singular and most beautiful representations of islands and hamlets, arched bridges Studies of Nature, stretched over wide rivers, immense ruins, huge rocks and gigantic mountains. The clouds frequently, among the Highlands of Scotland, display the finest outlines and assume the most lovely characters; more especially, when viewed from the cones of their wild and magnificent summits. To these landscapes, sketched with such boldness in the heavens, Dr. Beattie finelly alludes, in his poem of the Minstrel. Oft when the wintry storm had ceased to rave, Bloomfield describes the appearance of clouds, of a fine moonlight night, in a manner worthy the pen of Virgil: Low on the utmost bound'ry of the sight, Bloomfield's Winter, 1. 249. See this subject pursued in the Philosophy of Nature, Vol. I. p. 101. one of the most elegant and interesting works which modern times have produced. |