SIR WILLIAM HERSCHEL 119 



central points that it might not also exist without them. For this 

 opinion we may assign several reasons. One of them is the greater 

 resemblance of the chevelure of these stars and 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 independence of 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. Be- 

 sides, how impenetrable would be an atmosphere of a sufficient density 

 to reflect so great a quantity of light ! And yet we observe, 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 obstruction 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 constella- 

 tion of Orion, have been observed or suspected ; but some of them 

 are probably very distant, and run far out into space. For instance, 

 about 5m in time preceding x Cygni, Dr. H. suspects as much of it 

 as covers near 4 square degrees; and much about the same quantity 

 44m preceding the 125 Tauri. A space of almost 8 square degrees, 

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

 Three minutes preceding the 46 Eridani, strong, milky nebulosity is 

 expanded over more than 2 square degrees. Fifty-four minutes 

 preceding the 13th Caniim venaticomm, and again 48m preceding the 

 same star, the field of view afifected with whitish nebulosity through- 

 out the whole breadth of the sweep, which was 2° 39'. Four minutes 

 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 z}4th Piscium, very faint nebulosity appears 

 to be diffused over more than 9 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 



