379. The Nebula in Argus.—There is a nebula (Fig. 442) surrounding the variable star Eta Argus (355), which is remarkable as exhibiting variations of brightness and of outline.
In many other nebulæ, changes have been suspected; but the indistinctness of outline which characterizes most of these objects, and the very different aspect they present in telescopes of different powers, render it difficult to prove a change beyond a doubt.
380. The Dumb-Bell Nebula.—This nebula was named from its peculiar shape. It is a good illustration of the change in the appearance of a nebula when viewed with different magnifying powers. Fig. 443 shows it as it appeared in Herschel's telescope, and Fig. 444 as it appears in the great Parsonstown reflector (20).
Fig. 443.
Fig. 444.
Spiral Nebulæ.
381. The Spiral Nebula in Canes Venatici.—The great spiral nebula in the constellation Canes Venatici, or the Hunting-Dogs, is one of the most remarkable of its class. Fig. 445 shows this nebula as it appeared in Herschel's telescope, and Fig. 446 shows it as it appears in the Parsonstown reflector.