VOL. LXXXI.J PHILOSOPHICAL TRANSACTIONS. 25 



that are the occasion of the nebulosity which surrounds the central one? As, 

 by the former supposition, the luminous central point must far exceed the standard 

 of what we call a star, so, in the latter, the shining matter about the centre will 

 be rfiuch too small to come under the same denomination; we therefore either 

 have a central body which is not a star, or have a star which is involved in a 

 shining fluid, of a nature totally unknown to us. Dr. H. can adopt no other 

 sentiment than the latter, since the probability is certainly not for the existence 

 of so enormous a body as would be required to shine like a star of the 8th mag- 

 nitude, at a distance sufficiently great to cause a vast system of stars to put on 

 the appearance of a very diluted, milky nebulosity. 



But what a field of novelty is here opened to our conceptions! A shining 

 fluid, of a brightness sufficient to reach us from the remote regions of a star of 

 the 8th, gth, 10th, 1 1th, or 12th magnitude, and of an extent so considerable 

 as to take up 3, 4, 5, or 6 minutes in diameter! Can we compare it to the co- 

 ruscation of the electrical fluid in the aurora borealis? Or to the more magni- 

 ficent cone of the zodiacal light as we see it in spring or autumn? The latter, 

 notwithstanding Dr. H. has observed it to reach at least Q0° from the sun, is yet 

 of so little extent and brightness, as probably not to be perceived even by the 

 inhabitants of Saturn or the Georgian planet, and must be utterly invisible at the 

 remoteness of the nearest fixed star. 



More extensive views may be derived from this proof of the existence of a 

 shining matter. Perhaps it has been too hastily surmised that all milky nebulo- 

 sity, of which there is so much in the heavens, is owing to starlight only. 

 These nebulous stars may serve as a clue to unravel other mysterious phenomena. 

 If the shining fluid that surrounds them is not so essentially connected with these 

 nebulous stars but that it can also exist without them, which seems to be suffici- 

 ently probable, and will be examined hereafter, we may with great facility explain 

 that very extensive, telescopic nebulosity, which, as before-mentioned, is ex- 

 panded over more than 6o° of the heavens, about the constellation of Orion; a 

 luminous matter accounting much better for it than clustering stars at a distance. 

 In this case we may also pretty nearly guess at its situation, which must com- 

 mence somewhere about the range of the stars of the 7th magnitude, or a little 

 farther from us, and extend unequally in some places perhaps to the regions of 

 those of the gth, loth, nth, and 12th. The foundation for this surmise is, 

 that not unlikely some of the stars that happen to be situated in a more condensed 

 part of it, or that perhaps by their own attraction draw together some quantity 

 of this fluid greater than what they are entitled to by their situation in it, will of 

 course assume the appearance of cloudy stars; and many of those named are 

 either in this stratum of luminous matter, or very near it. 



VOL. XVII. E 



