Nebulous Matter. 315 



no longer present anything which ought to confound our 

 imagination. 



NEBULOUS MATTER. 



Let us pass from nebulae resolvable into stars by the aid of 

 powerful telescopes, to those which have never been sub- 

 jected to such decomposition, and turn our attention to those 

 masses of diffused luminous matter scattered here and there 

 in the firmament. 



The diffused matter occupies very extensive spaces in the 

 heavens. — Herschel published, in 1811, a catalogue of 52 dif- 

 fused nebulae, not resolvable, or at least not resolved, into 

 stars, among which some are to be found extending to 4** 9' 

 in one of their dimensions. The apparent superficial extent 

 of one of them exceeds that of nine circles of a degree in dia- 

 meter. The superficial extent of the whole together amounts 

 to 152 of these circles, which is about the 270th part of the 

 number of such circles which form the entire surface of the fir- 

 mament. 



The great luminous spots have no regular firm. — The forms 

 of the very large diffused nebulse do not appear susceptible of 

 definition ; they possess no regularity. They are found with 

 their contours rectilinear, curvilinear, and mixtilinear. Cer- 

 tain spots terminate distinctly, abruptly, and strongly marked 

 on one side, while on the opposite side they mingle with the 

 light of the sky by an insensible degradation. There are some 

 which throw out very long arms to a distance ; in others, large 

 obscure spaces are to be observed in the interior. All the fan- 

 tastical figures assumed by clouds carried along and agitated 

 by violent and often contrary winds, are found repeated in the 

 firmament of diffused nebulae. 



The diffused nebulae of a rounded form are not of gi'eat di- 

 mensions compared with the others. Sometimes (and this cir- 

 cumstance appears highly deserving of attention) there exists 

 between these rounded, very distinct, and well circumscribed 

 nebulae, a very slender thread of nebulosity attaching them 

 together by their circumferences ; one might call it a kind of 

 index, a visible witness to their common origin. 



