14 COSMOS. 



more irregularly diffused measure eight lunar diameters. Ac 

 cording to William Herschel's earlier estimate, made in 181 1, 

 these nebulous spots cover at least aTo^^ P^^^ ^^ ^^® whola 

 visible firmament. As seen through colossal telescopes, the 

 contemplation of these nebulous masses leads us into regions 

 %om whence a ray of light, according to an assumption not 

 iA'holly improbable, requires millions of years to reach our 

 ^arth, to distances for whose measurement the dimensions 

 <the distances of Sirius, or the calculated distances of the bi- 

 nary stars in Cygnus and the Centaur) of our nearest stra- 

 tum of fixed stars scarcely suffice. If these nebulous spota 

 be ellintical or spherical sidereal groups, their very conglom- 

 eration calls to mind the idea of a mysterious play of gravi 

 tative forces by which they are governed. If they be vapory 

 massns, having one or more nebulous nuclei, the various de- 

 r<rees of their condensation suggest the possibility of a process 

 of gradual star-formation from inglobate matter. No other 

 cosmical structure — no other subject of this branch of astron- 

 omy more contemplative than measuring — is, in like degree, 

 adapted to excite the imagination, not merely as a symbolic 

 imajgre of the infinitude of space, but because the investiga.- 

 tion of the different conditions of existing things, and of their 

 presumed connection of sequences, promises to afford us an in- 

 sight into the laws of genetic develojinient.^ 



The historical development of our knowledge of nebulou.s 

 bodies teaches us that here, as in the progress of almost every 

 other branch of physical science, the same opposite opinions, 

 which still have numerous adherents, were maintained long 

 since, although on weaker grounds. Since the general use 

 of the telescope, we find that Galileo, Dominique Cassini, 

 and the acute John Michell regarded all nebulse as remote 

 clusters of stars ; while Halley, Derham, Lacaille, Kant, and 

 Lambert maintained the existence of starless nebulous mass- 

 es. Kepler (like Tycho Brahe before the invention of the 

 telescope) was a zealous adherent of the theory of star-forma- 

 tion from cosmical vapor — from condensed conglobate celes 

 tial nebulous matter. He believed " cxli materiam tenuis 

 ummn (the vapor which shines with a mild stellar light ir 

 the Milky Way) in unum glohim condensatam, stella7n ef 

 fingere,'' and grounded his opinion, not on the process of con^ 

 densation operating in defined roundish nebulous spots (fox 

 those were unknown to him), but on the sudden appearance 

 0^ new stai 3 on the margin of the galaxy. 



* Cosmos, vol. i., p. 84. 



