In 1867, MM. Wolf and Rayet, of Paris, discovered that three yellow stars in the Swan, of about the eighth magnitude possessed the notable peculiarity of a bright-line spectrum. It was found by Raspighi and Le Sueur to be shared by one of the second order of brightness in Argo (γ Argûs), and Professor Pickering, of Harvard, reinforced the species, in 1880-81, with two further specimens. Dr. Copeland’s necessarily discursive operations on the shores of Lake Titicaca raised the number of its members at once from six to eleven or twelve. Now the smaller “planetary” nebulæ—so named by Sir William Herschel from the planet-like discs presented by the first-known and most conspicuous amongst them—are likewise only distinguished from minute stars by their spectra. Their light, when analysed with a prism, instead of running out into a parti-colored line, gathers itself into one or more bright dots. The position on the prismatic scale of those dots, alone serves to mark them off from the Wolf-Rayet family of stars. Hence the obvious inference that both nebulæ and stars (of this type) are bodies similar in character, but dissimilar in constitution—that they agree in the general plan of their structure, but differ in the particular quality of the substances glowing in the vast, incandescent atmospheres which display their characteristic bright lines in our almost infinitely remote spectroscopes. Indeed, the fundamental identity of the two species are virtually demonstrated, by the “migrations” (to use a Baconian phrase) of the “new star” of 1876, which, as its original conflagration died out, passed through the stages, successively, of a Wolf-Rayet or _nebular star_ (if we may be permitted to coin the term), and of a planetary nebula. So that not all the stars in space are suns—at least, not in the sense given to the word by our domestic experience in the solar system.