Astronomy for the use of schools and academies (1882) (14784308113)

Identifier: astronomyforuseo00gill (find matches)

Title: Astronomy for the use of schools and academies

Year: 1882 (1880s)

Authors: Gillet, J. A. (Joseph Anthony), 1837-1908 Rolfe, W. J. (William James), 1827-1910

Subjects: Astronomy

Publisher: New York : Potter, Ainsworth, & Co.

Contributing Library: The Library of Congress

Digitizing Sponsor: The Library of Congress

Text Appearing Before Image:

be the case, some portions of thering were much denser than others, the denser portions wouldgradually attract the rarer portions, until, instead of a ring,there would be a single mass composed of a nearly solidcentre, surrounded by an immense atmosphere of fiery vapor.This condensation of the ring of vapor around a single pointwould not change the amount of rotary motion that had existed 394 ASTRONOMY. in the ring. The planet with its atmosphere would there-fore be in rotation; and would be, on a smaller scale, like theoriginal solar mass surrounded by its atmosphere. In thesame way that the latter formed itself first into rings, whichafterwards condensed into planets, so the planetary atmos-pheres, if sufficiently extensive, would form themselves intorings, which would condense into satellites. In the case ofSaturn, however, one of the rings was so uniform throughout,that there was no denser portion to attract the rest around it;and thus the ring of Saturn retained its annular form.

Text Appearing After Image:

Fig. 456. Such is the celebrated nebular hypothesis of Laplace. Itstarts, not with a purely nebulous mass, but with the sun, sur-rounded by an immense atmosphere, out of which the planetswere formed by gradual condensation. Fig. 456 representsthe condensing mass according to this theory. 390. The Modern Nebular Hypothesis. — According to thenebular hypothesis as held at the present time, the sun, plan-ets, and meteoroids originated from a purely nebulous mass.This nebula first condensed into a nebulous star, the star beingthe sun, and its surrounding nebulosity being the fiery atmos-phere of Laplace. The original nebula must have been putinto rotation at the beginning. As it contracted and became ASTRONOMY. 395 condensed through the loss of heat by radiation into space,and under the combined attraction of gravity, cohesion, andaffinity, its speed of rotation increased; and the nebulousenvelop became, by the centrifugal force, flattened into a thindisk, which finally broke up into ri

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1882

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