There is a nest, or rather a cluster of nebulæ in the constellation of Coma Berenices; over a hundred of these objects being here gathered into a space of sky about the size of our full moon.
Plate XXIII. The Great Nebula in the Constellation of Andromeda
From a photograph taken at the Yerkes Observatory.
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The spectroscope informs us that spiral nebulæ are composed of partially-cooled matter. Their colour, as we have seen, is white. Nebulæ of a greenish tint are, on the other hand, found to be entirely in a gaseous condition. Just as the solar corona contains an unknown element, which for the time being has been called "Coronium," so do the gaseous nebulæ give evidence of the presence of another unknown element. To this Sir William Huggins has given the provisional name of "Nebulium."
The Magellanic Clouds are two patches of nebulous-looking light, more or less circular in form, which are situated in the southern hemisphere of the sky. They bear a certain resemblance to portions of the Milky Way, but are, however, not connected with it. They have received their name from the celebrated navigator, Magellan, who seems to have been one of the first persons to draw attention to them. "Nubeculæ" is another name by which they are known, the larger cloud being styled nubecula major and the smaller one nubecula minor. They contain within them stars, clusters, and gaseous nebulæ. No parallax has yet been found for any object which forms part of the nubeculæ, so it is very difficult to estimate at what distance from us they may lie. They are, however, considered to be well within our stellar universe.
Having thus brought to a conclusion our all too brief review of the stars and the nebulæ—of the leading objects in fine which the celestial spaces have revealed to man—we will close this chapter with a recent summation by Sir David Gill of the relations which appear to obtain between these various bodies. "Huggins's spectroscope," he says, "has shown that many nebulæ are not stars at all; that many well-condensed nebulæ, as well as vast patches of nebulous light in the sky, are but inchoate masses of luminous gas. Evidence upon evidence has accumulated to show that such nebulæ consist of the matter out of which stars (i.e. suns) have been and are being evolved. The different types of star spectra form such a complete and gradual sequence (from simple spectra resembling those of nebulæ onwards through types of gradually increasing complexity) as to suggest that we have before us, written in the cryptograms of these spectra, the complete story of the evolution of suns from the inchoate nebula onwards to the most active sun (like our own), and then downward to the almost heatless and invisible ball. The period during which human life has existed upon our globe is probably too short—even if our first parents had begun the work—to afford observational proof of such a cycle of change in any particular star; but the fact of such evolution, with the evidence before us, can hardly be doubted."[34]
