26 PHILOSOPHICAL TRANSACTIONS. [aNNO IJQl- 



It has been said above, that in nebulous stars the existence of the shining 

 fluid does not seem to be so essentially connected with the central points that it 

 might not also exist without them. For this opinion we may assign several rea- 

 sons. One of" them is the great resemblance between the chevelure of these 

 stars anrl the diffused extensive nebulosity mentioned before, which renders it 

 highly probable that they are of the same nature. Now, if this be admitted, 

 the separate existence of the luminous matter, or its independance on a central 

 star, is fully proved. We may also judge, very confidently, that the light of 

 this shining fluid is no kind of reflection from the star in the centre; for, as we 

 have already observed, reflected light could never reach us at the great distance 

 we are from such objects. Besides, how impenetrable would be an atmosphere 

 of a sufficient density to reflect so great a quantity of light.'' And yet we ob- 

 serve, that the outward parts of the chevelure are nearly as bright as those that 

 are close to the star; so that this supposed atmosphere ought to give no obstruc- 

 tion to the passage of the central rays. If therefore this matter is self-luminous, 

 it seems more fit to produce a star by its condensation than to depend on the star 

 for its existence. 



Many other diffused nebulosities, besides that about the constellation of Orion, 

 have been observed or suspected; but some of them are probably very distant, 

 and run out far into space. For instance, about 5^" in time preceding g Cygni, 

 Dr. H. suspects as much of it as covers near 4 square degrees; and much about 

 the same quantity 44™ preceding the 125 Tauri. A space of almost 8 square 

 degrees, 6"" preceding a. Trianguli, seems to be tinged with milky nebulosity. 

 Three minutes preceding the 40 Eridani, strong, milky nebulosity is expanded 

 over more than 2 square degrees. 54"^ preceding the 13th Canum venaticorum, 

 and again 48"^ preceding the same star, the field of view aftected with whitish 

 nebulosity throughout the whole breadth of the sweep, which was 2° 3Q'. 4™ 

 following the 57 Cygni, a considerable space is filled with faint, milky nebulosity, 

 which is pretty bright in some places, and contains the 37th nebula of the 5th 

 class, in the brightest part of it. In the neighbourhood of the 44th Piscium, 

 very faint nebulosity appears to be diffused over more than Q square degrees of 

 the heavens. Now all these phenomena, as we have already seen, will admit of 

 a much easier explanation by a luminous fluid than by stars at an immense 

 distance. 



The nature of planetary nebulae, which has hitherto been involved in much 

 darkness, may now be explained with some degree of satisfaction, since the uni- 

 form and very considerable brightness of their apparent disc accords remarkably 

 well with a much condensed, luminous fluid; whereas, to suppose them to con- 

 sist of clustering stars, will not so completely account for the milkiness or soft 



