There also exist nebulæ of _irregular_ form, the most notable being the Great Nebula in the constellation of Orion (see Plate XXIV., p. 318). It is situated in the centre of the "Sword" of Orion (see Plate XX., p. 296). In large telescopes it appears as a magnificent object, and in actual dimensions it must be much on the same scale as the Andromeda Nebula. The spectroscope tells us that it is a mass of glowing gas. The Trifid Nebula, situated in the constellation of Sagittarius, is an object of very strange shape. Three dark clefts radiate from its centre, giving it an appearance as if it had been torn into shreds. The Dumb-bell Nebula, a celebrated object, so called from its likeness to a dumb-bell, turns out, from recent photographs taken by Professor Schaeberle, which bring additional detail into view, to be after all a great spiral. 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. [Illustration: PLATE XXIII. THE GREAT NEBULA IN THE CONSTELLATION OF ANDROMEDA From a photograph taken at the Yerkes Observatory. (Page 314)] 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.