The fantastic variety of nebular forms was long a subject of wonder, scarcely tempered by a speculative effort. Inchoate worlds, disclosed with astonishing profusion by Herschel's telescopes, seemed like mere ‘sports of nature’ in the sidereal spaces. Nebulæ were to be found in the semblance of rings, fans, brushes, spindles; they abounded in planetary, cometary, elliptical, branching varieties; nebulous shields, embossed with stars, or tasselled like the ægis of Athene, displayed themselves, as well as nebulous dises, rays, filaments, triangles, parallelograms, twin and triple spheres. One nebula, thought to resemble the face of an owl, was named accordingly; another suggested a crab; a third a swan; a fourth (the great Orion formation) became known as the Fish Mouth nebula, from its supposed likeness to the gaping jaws of a marine monster. Fancy ranged at large through this wide realm, attempting to familiarise itself with the strange objects contained in it by finding for them terrestrial similitudes.

Within the last few years, however—indeed, it may be said, since the completion of the Rosse reflector in 1845—nebular inquiries have entered upon a new phase. A ‘glimmering of reason’ has begun to hover over what long appeared a scene of hopeless bewilderment. With improved telescopic means—above all, with the aid of photography—structure has become increasingly manifest among all classes of nebulæ; structure, not of a finished kind, but indicating with great probability the advance of formative processes on an enormous scale, both as regards space and time.