The hypothesis of the original nebular condition of the system, with the consequent explanation of the great phenomena of planetary formations and movements of the satellites and rings, is unquestionably to be assigned to Kant.
In his Naturgeschichte des Himmels, in which he anticipated the nebular theory afterwards more fully developed by Laplace, Kant sought to explain the genesis of the cosmos as a product of physical forces and laws.
NEBULAR THEORY, a theory advanced to account for the origin of the solar system.
Yet the boldness and the splendour of the nebular theory have always given it a dignity not usually attached to a doctrine which from the very nature of the case can have but little direct evidence in its favour.
On these grounds we discuss the nebular theory without much reference to comets.
The nebular theory offers an explanation of this most remarkable uniformity.
Such was the nebular theory as it was originally sketched.
At the present day when the nebulae that are spiral in form have been shown to be so numerous, next to the fixed stars themselves, our view of the nebular theory has been somewhat modified.
The rotation of the planets on their axes is also explained as a consequence of the nebular theory, for at the time of the first formation of the planet it must have participated in the rotation of the whole nebula, and by the subsequent contraction of the planet the speed with which the rotation was performed must have been accelerated.
There is quite a different method of considering the nebular origin of our system, which leads in a very striking manner to conclusions practically identical with those we have just sketched.
The daily outpour of heat from the sun at the present time suggests a profound argument in support of the nebular theory.
The nebular theory is a noble speculation supported by plausible argument, and the verdict of science on the whole subject cannot be better expressed than in the words of S.
Newcomb: "At the present time we can only say that the nebular hypothesis is indicated by the general tendencies of the laws of nature, that it has not been proved to be inconsistent with any fact, that it is almost a necessary consequence of the only theory by which we can account for the origin and conservation of the sun's heat, but that it rests on the assumption that this conservation is to be explained by the laws of nature as we now see them in operation.
The famous "nebular hypothesis" of Laplace made its appearance in the Systeme du monde.
It is curious that Laplace, while bestowing more attention than they deserved on the crude conjectures of Buffon, seems to have been unaware that he had been, to some extent, anticipated by Kant, who had put forward in 1755, in his Allgemeine Naturgeschichte, a true though defective nebular cosmogony.
This is at once connected with the nebular hypothesis, and subsequently deduced "from the ultimate law of the" persistence of force,"and finally supplemented by a counter-process of dissolution, all of which appears to Spencer only as" the addition of Von Baer's law to a number of ideas that were in harmony with it."It is clear, however, that Spencer's ideas as to the nature of evolution were already pretty definite when Darwin's Origin of Species (1859) revolutionized the subject of organic evolution by adding natural selection to the direct adaptation by use and disuse, and so suggesting an intelligible method of producing modifications in the forms of life.
He was also a great physicist and had arrived at the nebular hypothesis theory of the formation of the planets and the sun long before Kant and Laplace.
Thus in 1864 the spectroscope yielded him evidence that planetary and irregular nebulae consist of luminous gas - a conclusion tending to support the nebular hypothesis of the origin of stars and planets by condensation from glowing masses of fluid material.
In this remarkable work Kant, proceeding from the Newtonian conception of the solar system, extends his consideration to the entire sidereal system, points out how the whole may be mechanically regarded, and throws out the important speculation which has since received the title of the nebular hypothesis.
19th century, both the use and the improvement of reflectors were left mainly in British hands; but the gift of the " Crossley " instrument in 1895, to the Lick observatory, and its splendid subsequent performances in nebular photography, brought similar tools of research into extensive use among American astronomers; and they are now, for many of the various purposes of astrophysics, strongly preferred to refractors.
Nebular chemistry was initiated by the same investigator when, on the 29th of August 1864, he observed the bright-line spectrum of a planetary nebula in Draco.
Sions be secured of such faint objects as nebulae, tele scopic comets, and the immense majority of stars, or of the dim ranges of stellar and nebular spectra.
Again by Sir William Huggins, the spectrum of the Orion nebula was photographed on the 7th of March 1882; and the method has gradually become nearly exclusive in the study of nebular emanations.