14, COSMOS, 



more irregularly diffused measure eight lunar diameters, Ac 

 cording to William Herschel's earlier estimate, made in 1811, 

 these nebulous spots cover at least 2 7 o^^ P^^^ of the whole 

 visible firmament. As seen through colossal telescopes, the 

 contemplation of these nebulous masses leads us into regions 

 .from w^hence a ray of light, according to an assumption not 

 A^holly improbable, requires millions of years to reach our 

 »5arth, 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 spots 

 be elliptical 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 

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

 crees of their condensation suggest the possibility of a process 

 of gradual star-formation from inglobate matter. No other 

 cosroical 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 

 ima^e 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 oi genetic development.^ 



The historical development of our knowledge of nebulous 

 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 " codi materiam tenuis- 

 simam (the vapor which shines with a mild stellar light in 

 the Milky Way) in unum glohum condensatam, stellam ef- 

 jingere^ and grounded his opinion, not on the process of con- 

 densation operating in defined roundish nebuloUs spots (for 

 those were unknown to him), but on the sudden a,ppearance 

 of new stars on the margin of the galaxy. 

 ♦ Cosmos, vol. i., p. 84. 



