Nebular Hypothesis
2 of the 7 encyclopedias on this shelf carry an entry for Nebular Hypothesis. Both are reproduced below, so you can see where they agree and where they differ.
Collier's New Encyclopedia (1921)
in astronomy, a hypothesis nesis first suggested by Sir William Herschel, though the germs of it may be found in Kant's "General Natural History and Theory of the Heavens," printed in 1755. It was de. veloped by La Place, with whose name it came to be associated. The hypothesis assumes that originally all suns were in a nebulous or ultra-gaseous state. The nebulous matter from which they were originally formed was at first scattered pretty uniformly through all space, but ultimately began to gravitate toward certain centers. Further contraction producing increased velocity, ring after ring would be cast off, till the central body or sun generated a whole system of planets revolving around it. They, in turn, might in the same way produce satellites. La Place believed that the sun thus produced our earth and the other attendant planets. On this hypothesis the rings of Saturn were produced by Saturn himself, and have remained in the annular form instead of condensing into nearly spherical satellites. Many people supposed that the resolution of various nebulæ into stars (see NEBULA) was necessarily fatal to the nebular hypothesis, but the discovery that some are not only irresolvable, but can be actually proved by spectrum a analysis to consist of glowing gas, has re-established it on a firmer basis than ever, though the original the ory may need revision in points of detail.
Aiton's Encyclopedia (1910)
in astronomy, a theory of the formation of the solar system . It was propounded originally by Swedenborg and was passed on by Kant to La Place, "the French Newton," who elaborated the theory and gave it currency. It is associated usually with the name of La Place. According to this theory the material of which the present solar system--sun, planets, moons, and asteroids--is composed was distributed in a vast gaseous mass extending beyond the orbit of Neptune. Under the influence of gravitation and motion the mass contracted, throwing off planet after planet, the remotest planet first. The sun, at the center, is what was left after the mass became reduced sufficiently to hang together. La Place was of the opinion that each planet disengaged itself from the central mass in the form of a ring, such as now surrounds the planet Saturn. The moons of each planet are supposed to have been thrown off from the planets around which they revolve. The entire theory is undergoing study at the present time. It has been suggested, for instance, that our moon and the other moons are captured planets, or comets, that is to say, that they formerly described orbits about the sun, but that they came so near the planets they now attend, that they were captured, drawn within the influence of their respective planets, and thus became satellites.