STAR-SYSTEMS NEBULA. 181 



divided through a certain extent into two branches. The diagram may help to illustrate 

 this view of the architecture of the visible stellar universe, the small circle indicating the 



place of the solar system in it. It was the idea of Herschel, that the thickness and 

 greatest elongation of this bed of stars might be equal respectively to eight and nine 

 hundred times the distance of the nearest of the fixed stars from our system ; and that our 

 place in it is eccentric in relation both to the surfaces and the extremities. 



We thus pass from the grand idea of an individual sun or star, with attendant planets, 

 forming a solar system, to the incomparably grander conception of a vast mass, cluster, or 

 universe of solar systems, many perhaps surpassing our own in magnitude, and doubtless 

 held together in definite arrangement and unbroken harmony by the bond of gravitation. 

 Yet this stellar scheme, mighty as are its dimensions, is but a sample of the contents of 

 celestial space a single member in a numerous family of similar sidereal assemblages, 

 within hail of the modern telescope. These remote groups, "island universes" as the 

 Germans call them, a few of which may be detected by the naked eye, are generally spoken 

 of collectively as nebulce, from their cloud-like appearance, a denomination applied to them 

 long before their real character was known or suspected. They vary considerably in shape, 

 size, and luminosity ; and occur in numbers, which every improvement of the telescope 

 increases. In Halley's time the whole number known amounted to six ; but he naively 

 remarked, "there are undoubtedly more which have not yet come to our knowledge.** 

 Messier, the " comet-ferret," was the first who paid particular attention to these objects. 

 While looking for Halley's comet, in 1758, whose return was then expected, he observed 

 in the neighbourhood of ? Tauri a whitish light, elongated like the flame of a taper. This 

 led to the production of his list of these objects, containing a hundred and three, the result 

 of his own personal observation. It appeared in the Connaissance des Temps, for the year 

 1784, an astronomical almanac published by the French Board of Longitude. Herschel 

 discovered upwards of two thousand more, whose places were determined and catalogued 

 by his sister. Sir John Herschel commenced in 1825 and finished in 1833 the most 

 complete catalogue of nebulae, containing his father's results, and five hundred additional 

 objects, the fruits of his own observation. " I have already determined," he remarks, 

 " with as much accuracy as the nature of such observations permits, the places ; and 

 obtained sufficient descriptions of the physical peculiarities, of between two and three 

 thousand of these wonderful objects a great part of them by many repeated observations, 

 and made careful drawings of the most remarkable for their shape, size, or structure. 



