Page:Popular Science Monthly Volume 9.djvu/688

660 objects we are gazing at works in process of formation as they lie plastic under the creative hand of the Almighty. Nor is it possible to withhold the inference—thus probably was the world we live in, and the solar system of which we form a part, evolved out of chaos.

The labors of Laplace commenced where Herschel ended. Herschel described what he saw. Laplace showed by mathematics how the known laws of gravitation could form, and probably did form, from such partially-condensed mass of matter an entire planetary system.

It is supposed that a film of vaporous matter filled up the space which is now bounded by the orbit of the outermost planet of our system. To the eye of an observer, if such there were, in a distant star such a vapor would appear like one of the numerous nebulæ which are everywhere visible in the heavens.

Laplace supposed that this nebula, extending beyond what is now the orbit of Neptune, possessed a rotatory motion round its centre of gravity, and that the parts of it which were situated at the limits where the centrifugal force exactly counterbalanced the attractive force of the central nucleus were abandoned by the central mass. Thus, as the nucleus became more and more dense under the action of gravity, were formed a succession of rings concentric with and revolving round the centre of gravity. Each ring would break up into masses which would be endued with motions of rotation, and would in consequence assume a spheroidal form. These masses formed the various planets, which, in their turn condensing, cast off in some instances their outlying rings, as the central mass had done, and thus formed the moons or satellites which accompany the planets. As each planet was in turn cast off, the central mass contracted itself within the orbit of that last formed, till, after casting off Mercury, it gathered with immense energy round its own centre and formed the sun.

Laplace's mechanical explanation does not rest only on theory. It has been experimentally shown that matter under certain conditions would exhibit phenomena similar in many important particulars to those which Laplace was led by mathematical considerations to suppose. Prof. Plateau, several years ago, tried the experiment of pouring olive-oil into alcohol and water, mixed in such proportions as exactly to equal the density of the oil. The oil thus became a liquid mass relieved from the operation of gravity, and free to take any exterior form which might be imposed by such forces as might be brought to bear upon it. The oil instantly took the form of a globe by virtue of molecular attraction. Prof. Plateau then introduced a wire into the globe of oil in such a manner as to form for it a vertical axis. The wire had on it a little disk coincident with the centre of the globular mass, and by turning the axis the oil was made to revolve. The sphere soon flattened at the poles and bulged out at the equator, thus producing on a small scale an effect which is admitted