GRAVITATION.
The Forms of Matter—Shape of the Earth—Probability of the Mass forming this Planet having existed in a Nebulous State—Zodiacal Lights—Comets—Volatilization of Solid Matter by Artificial means—The principle of Gravitation—Its Influence through Space and within the smallest Limits—Gravitating powers of the Planets—Density of the Earth—Certainty of Newton’s Law of the Inverse Square—Discovery of Neptune—State of a Body relieved from Gravitation—Experiment explaining Saturn’s Ring, &c.—General inference.
Let us suppose the earth—consisting of three conditions of matter; the solid, the fluid, and the aëriform—to be set free from that power by which it is retained in its present form of a spheroid flattened at the poles, but still subject to the influences of its diurnal and annual rotations. Agreeably to the law which regulates the conditions of all bodies moving at high velocities, the consequence of such a state of things would be, that our planet would instantly spread itself over an enormous area. The waters and even the solid masses of this globe would, in all probability, present themselves amidst the other phenomena of space in a highly attenuated state, revolving in an orbit around the sun, as a band of nebulous matter, which might sometimes be rendered sensible to sight by still reflecting solar light, or by condensation in the form of flights of shooting stars.[13]
This may be illustrated by experiment. If upon a rapidly revolving disc we place a ball of dust, it will be almost immediately spread out, and its particles will arrange themselves in a series of regular curves, varying with the velocity of the motion. In addition to the disintegration which would arise from the tendency of the atoms to fly from the centre, the motion, in space, of the planetary mass would naturally occasion a trailing out, and the only degree of uniformity which this orb could, under these imaginary conditions, possibly present, would be derived from the combined effects of motions in different directions.
Amid the remoter stars, some remarkable cloud-like appearances are discovered. These nebulæ, presenting to the eye of the observer only a gleaming light, as from some phosphorescent vapour, were long regarded as indications of such a condition as that which we have just been considering. Astronomers saw, in those mysterious nebulæ, a confirmation of their views, which regarded all the orbs of the firmament as having once been thin sheets of vapour, which had gradually, from irregular bodies traversing space, been slowly condensed about a centre, and brought within the limits of aggregating agencies, until, after the lapse of ages, they become sphered stars, moving in harmony amid the bright host of heaven.[14] Geologists seized on those views with eagerness, as confirming theoretical conclusions deduced from an examination of the structure of the earth itself, and explained by them the gradual accretion of atoms into crystalline rocks from a cooling mass.
The researches of modern astronomers, aided by the magnificent instruments of Lord Rosse,[15] have, however, shown that many of the most remarkable nebulæ are only clusters of stars; so remote from us, that the light from them appears blended into one diffused sheet or luminous film. There are, however, the Magellanic clouds, and other singular patches of light, exhibiting changes which can only be explained on the theory of their slow condensation. There is no evidence to disprove the position that world-formation may still be going on; that a slow and gradual aggregation of particles, under the influence of laws with which we are acquainted, may be constantly in progress, to end, eventually, in the formation of a sphere.
May we not regard the zodiacal light as the remains of a solar luminiferous atmosphere, which once embraced the entire system of which it is the centre?[16] Will not the strange changes which have been seen to take place in cometary bodies, even whilst they were passing near the earth,—as the division of Biela’s comet and the ultimate formation of a second nucleus from the detached portion,—strongly tend to support the probability of the idea that attenuated matter has, in the progress of time, been condensed into solid masses, and that nebulous clouds must still exist in every state of tenuity in the regions of infinite space,[17] which, in the mysterious processes of world-formation, will, eventually, become stars, and reflect across the blue immensity of heaven, in brightness, that light which is the necessary agent of organisation and all manifestations of beauty?
The inferences drawn from a careful study of the condition of our own globe are in favour of the assumption of the existence of nebulous matter. By the processes of art and manufacture, by the operation of those powers on which organisation and life depend, solid matter is constantly poured off in such a state that it cannot be detected, as matter, by any of the human senses. Yet a thousand results, daily and hourly accumulating as truths around us, prove that the solid metals, the gross earths, and the constituents of animal and vegetable life, all pass away invisible to us, and become “thin air.” We know that, floating around us, these volatilized bodies exist in some material form, and numerous experiments in chemistry are calculated to convince us, that the most attenuated air is capable, with a slight change of circumstances, of being converted into the condition of solid masses. Hydrogen gas, the lightest, the most ethereal of the chemical elements, dissolves iron and zinc, arsenic, sulphur, and carbon; and from the transparent combinations thus formed, we can with facility separate those ponderous bodies. Such substances must exist in our own atmosphere; why not in the regions of space? Whether this planet ever floated a mass of nebulous matter, only known by its dim and filmy light, or comet-like rushed through space with widely eccentric orbit, are questions which can only receive the reply of speculative minds. Whether the earth and the other members of the Solar System were ever parts of a Central Sun,[18] and thrown from it by some mighty convulsion, though now revolving with all the other masses around that orb, chained in their circuits by some infinite power, is beyond the utmost refinements of science to discover. This hypothesis is, however, in its sublime conception, worthy of the master-mind that gave it birth.