We know nothing quantitatively of the radiations from a nebulous body; and it is quite possible that the loss of radiant energy in this early stage was very small; but it is at least as certain as any other physical inference that 17,000,000 years ago the earth itself was of its present dimensions, a comparatively old body with sea and living creatures upon it, and it is impossible to believe that the sun's radiations were wholly different; but, if they were not, they have been maintained from some other source than contraction.
Since the reactions occur among gases and liquids in the nebulous state, vast spaces have to be provided in which the process may be carried out as completely as possible before the waste gases are allowed to escape into the outer air.
Little inclined by nature to any but the emotional side of religion, and utterly undisciplined in any other by education, course of life, or the general tendency of public opinion, Rousseau naturally took refuge in the nebulous kind of natural religion° which was at once fashionable and convenient.
Further, he showed that the spectrum of a dense ignited gas resembles that of an incandescent liquid or solid, and he traced a gradual change in the spectrum of an incandescent gas under increasing pressure, the sharp lines observable when it is extremely attenuated broadening out to nebulous bands as the pressure rises, till they merge in the continuous spectrum as the gas approaches a density comparable with that of the liquid state.
When the formula cited is not used, other somewhat nebulous expressions are sometimes employed, as, for example, that.
The collision theory supposes that the outburst is the result of a collision between two stars or between a star and a swarm of meteoric or nebulous matter.
As early as 1860 Newcomb communicated an important memoir to the American Academy, 4 On the Secular Variations and Mutual Relation of the Orbits of the Asteroids, in which he discussed the two principal hypotheses to account for the origin of these bodies - one, that they are the shattered fragments of a single planet (Olbers' hypothesis), the other, that they have been formed by the breaking up of a revolving ring of nebulous matter.
If we are dealing with comparatively recent periods there is no evidence of progressive change, but if we go to remote epochs and suppose the sun to have once been diffused in a nebulous state, it is clear that its shrinkage, in spite of radiation, has left it hotter, so that the shrinkage has outrun what would suffice to maintain its radiation.
We have thus grounds for believing that the original nebula will separate into a series of rings all revolving in the same direction with a central nebulous mass in the interior.
These differ in that comets are visible either in a telescope or to the naked eye, and seem to be either wholly or partially of a nebulous or gaseous character, while meteors are, individually at least, invisible to us except as they become incandescent by striking the atmosphere of the earth.
This tradition, however, is nebulous in the extreme; the whole list of kings, which it gives, is totally unhistorical; only the names of one Balash (=Vologaeses) and of the last Ardewan (=Artabanus) having been preserved.
The transition from an object of this kind to a nebulous star is very natural, while the nebulous stars pass into the ordinary stars by a few graduated stages.
While at the close of the 19th century western Asia (exclusive of Arabia) may be said to have been freed from all geographical perplexity, China, Mongolia and eastern Siberia still include enormous areas of which geographical knowledge is in a primitive stage of nebulous uncertainty.