VOL, LXXXI.] VHILOSOPHICAL TRANSACTIONS. 21 



naturally to give us the idea of a conjunction in the things that produce it. And 

 a considerable addition to this argument may be derived from a repetition of the 

 same phenomenon, in Q or 10 more of a similar construction. 



When Dr. H. examined the cluster of stars, following the head of the Great 

 Dog, he found on March IQ, 1786, that there was within this cluster a round, 

 resolvable nebula, of about 2' in diameter, and nearly of an equal degree of light 

 throughout. Here, considering that the cluster was free from nebulosity in other 

 parts, and that many such clusters, as well as many such nebulae, exist in divers 

 parts of the heavens, it appeared very probable, that the nebula was unconnected 

 with the cluster; and that a similar reason would as easily account for this appear- 

 ance as it had resolved the phenomenon of the double star near £ Bootis ; that is, 

 a casual situation of our sun and the two other objects nearly in a line. And 

 though it may be rather more remarkable, that this should happen with 2 com- 

 pound systems, which are not by far so numerous as single stars, we have, to 

 make up for this singularity, a much larger space in which it may take place, the 

 cluster being of a very considerable extent. 



On Feb. 15, 1786, Dr. H. discovered that one of his planetary nebulae, had a 

 spot in the centre, which was more luminous than the rest, and with long atten- 

 tion, a very bright, round, well defined centre became visible. He remained 

 not a single moment in doubt, but that the bright centre was connected with the 

 rest of the apparent disc. Oct. 6, 1785, he found a very bright, round nebula, 

 of about 1-1-' in diameter. It has a large, bright nucleus in the middle, which is 

 undoubtedly connected with the luminous parts about it. And though we must 

 confess, that if this phenomenon, and many more of the same nature, recorded 

 in the catalogues of nebulae, consist of clustering stars, we find ourselves involved 

 in some difficulty to account for the extraordinary condensation of them about 

 the centre ; yet the idea of a connection between the outward parts and these 

 very condensed ones within, is by no means lessened on that account. 



There is a telescopic milky way, which Dr. H. has traced out in the heavens in 

 many sweeps made from the year 1783 to 1789. It takes up a space of more 

 than 60 square degrees of the heavens, and there are thousands of stars scattered 

 over it : among others, 4 that form a trapezium, and are situated in the well 

 known nebula of Orion, which is included in the above extent. All these stars, 

 as well as the 4 mentioned, he takes to be entirely unconnected with the nebu- 

 losity which involves them in appearance. Aniong them is also d Ononis, a 

 cloudy star, improperly so called by former astronomers ; but it does not seem to 

 be connected with the milkiness any more than the rest. 



Dr. H. comes now to some other phenomena, that, from their singularity, 

 merit undoubtedly a very full discussion. Among the reasons which induced us 

 to embrace the opinion, that all very faint milky nebulosity ought to be ascribed 



