When seventy dark lines on the spectrum of the star Aldebaran, and eighty on that of α Orionis (Betelgeux) were compared with the bright lines on the spectra of the vapours of a variety of the terrestrial simple elements, it was found that Aldebaran contained nine terrestrial substances and α Orionis five: that is, there were only nine out of seventy of the dark lines of Aldebaran coincident with bright lines, and five out of eighty of those of α Orionis. Yet the seventy and eighty dark lines that were compared represented some of the strongest only of the numerous lines which were seen on the spectra of these stars. Some of those remaining were probably due to the vapours of other terrestrial elements which were not compared with these stars, but Mr. Huggins concludes that many of those dark lines are due to new unknown elements existing in these stars, and that we cannot assume that the sixty-five simple terrestrial elements constitute the entire primary material of the universe. A community of matter, however, exists throughout the visible creation; for the stars contain many of the elements common to the sun and earth. ‘It is remarkable that the elements most widely diffused through the host of stars are some of those most closely connected with the living organism of our globe, including hydrogen, sodium, magnesium and iron. May it not be that, at least, the brighter stars are like our sun, the upholding and energizing centres of systems of worlds adapted to the abode of living beings?’
With regard to the nebulæ Mr. Huggins’s observations show that nine are gaseous, the spectra of six exhibiting three bright lines, one shows an additional faint line also, while the spectra of the dumb-bell nebula and the annular nebula in Lyra show the brightness of three green lines only. The spectra of eight other nebulæ were continuous, showing that their light has not undergone any modification on its way to us.
Mr. Huggins has been able to discriminate between the light of the nucleus of a comet and that of its tail. The nucleus is self-luminous, and its substance is in the form of ignited gas. The coma shines by reflected light as clouds do, and observations of the spectra give reason to believe that comets chiefly consist of nitrogen and another elementary body different from nitrogen combined with it.
The terrestrial elements found in the fixed stars show that, like the sun, they have an intensely luminous nucleus: but if it be taken for granted that highly heated gases are non-luminous internally, the planetary nebula and the great nebula in Orion itself being thus considered to be gaseous, must emit their feeble light from their surfaces alone. All the true clusters of stars which are resolved by the telescope into distinct bright points of light, give a spectrum which does not consist of separate bright lines, but is apparently continuous in its light. The great nebula in Andromeda, which is visible to the naked eye, has an apparently continuous spectrum, but the whole of the red and orange part is wanting, and the brighter parts have a mottled appearance. The easily resolvable cluster in Hercules has a similar spectrum; Lord Rosse discovered dark streaks or lines in both.
There is a striking correspondence between the results of prismatic and telescopic observations; half of the nebulæ which have a continuous spectrum have been resolved into stars, while none of the gaseous nebulæ have been resolved even by Lord Rosse’s telescope. Thus it appears probable that primordial nebulous matter does exist, according to the theories of Sir William Herschel and La Place.
The structure of the sun himself, which forms one amidst the multitude of stars which constitute the Milky Way; and the maintenance of his light and heat without apparent waste, are still in various respects involved in mystery.
The luminous gaseous atmosphere of the sun is of great extent and of lower temperature, at least in its upper regions, than the photosphere on which it rests. Mr. De la Rue’s photographs of the sun show that the light from the border of the solar disc is less intense than that from the equator, on account of the greater depth of solar atmosphere it has to pass through before it reaches the earth, by which a larger portion of the light is absorbed.
The photosphere of the sun has a mottled appearance, exhibiting minute masses, which must be of enormous magnitude to be visible at such a distance. They have been examined with a very high telescopic power by Mr. Nasmyth, who describes them as lens-shaped bodies of wonderful uniformity, and likens them to willow leaves crossing each other in all directions, and moving irregularly among themselves. Mr. De la Rue and Padre Secchi say they have seen something similar, and others liken them to rice grains. Sir John Herschel[[26]] is of opinion that they consist of incandescent matter sustained at a level corresponding to their density in the solar atmosphere, an atmosphere which he considers as varying from a liquid state below to the highest tenuity of a rarefied gas above. In a memoir read at the Institute of Paris,[[27]] by M. Faye, something of the same kind is suggested.
There are comparatively brighter waves of the sun’s disc, called faculæ, which are portions of the sun’s photosphere thrown up into the higher regions of his atmosphere; for Mr. De la Rue took a stereoscopic impression of a solar spot and some faculæ, in which the spot appeared to be a hollow and the faculæ elevated ridges. Being elevated above the photosphere, their light is less absorbed by the sun’s atmosphere, and by contrast they are brighter at the less luminous border of the solar disc than at the equator.
It appears that the red flames and protuberances seen round the edge of the sun during a total eclipse are gaseous or vaporous luminous bodies which certainly belong to the sun; for during the total eclipse in 1860 it was observed, that as the moon moved over the sun’s disc, the red flames and part of the corona discovered themselves at the side which she had left, and were covered by her disc at the side towards which she was approaching. Besides, the illuminating effect of the red light of these flames is so inferior to its photographic power, that Mr. De la Rue photographed one of the protuberances, although it was invisible to the naked eye.