26 COSMOS. 



from 1786 to 1802, and the above-named great exploration 

 of the heavens published by his son in the Philos. Transact. 

 of 1833 ; and b. to the portion of the southern heavens visi- 

 ble at the Cape of Good Hope, according to Sir John Her- 

 schel's African Catalogues, nebulae and clusters of stars are 

 set down indiscriminately together. I have, however, deemed 

 it best, notwithstanding the natural affinity of these objects, 

 to enumerate them separately, in order to indicate a definite 

 epoch in the history of their discovery. I find that the North- 

 ern Catalogue* contains 2299 nebulae ana 1 152 clusters of 

 stars ; the Southern or Cape Catalogue, 1239 nebulas and 

 236 clusters of stars. We have, therefore, 3538 for the num- 

 ber of the neLulce throughout the firmament which were given 

 in these catalogues as not yet resolved into clusters. This 

 number may, perhaps, be increased to 4000, if we take into 

 account 300 or 400 seen by Sir William HerscheLf but not 

 again determined, and the 629 observed by Dunlop at Para- 



* The data on which these numbers are based require some expla- 

 nation. The three catalogues of the elder Herschel contain 2500 objects, 

 viz., 2303 nebulae and 197 clusters of stars. (Macller, Astr., p. 448.) 

 These numbers were altered in the subsequent and far more exact ex- 

 ploration made by Sir John Herschel (Observations of Nebulae and Clus- 

 ters of Stars made at Slough with a twenty-feet reflector, between the 

 years 1825 and 1833, in the Philosophical Transactions of the Royal 

 Society of London for the year 1833, p. 365-481). About 1800 objects 

 were identical with those of the three earlier catalogues; but 300 or 400 

 were temporarily excluded, and more than 500 newly discovered were 

 determined according to Right Ascension and Declination. (Struve, 

 Astr. Stellaire, p. 48.) The Northern Catalogue contains 152 clusters 

 of stars, consequently 2307 152=2155 nebula; but, in reference to 

 the Southern Catalogue (Observations at the Cape, p. 3, 6, 7), we have 

 to subtract from the 4015 2307 = 1708 objects, among which there are 

 236 clusters of stars (see Op. cit., p. 3. 6, 7, p. 128), 233, viz., 89-}- 

 135-J-9, as belonging to the Northern Catalogue, and observed by Sir 

 William and Sir John Herschel at Slough, and by Messier in Paris. 

 There remain, therefore, for the Cape observations, 1708 233=1475 

 nebulae and clusters of stars, or 1239 nebulae alone. We have, how- 

 ever, to add 135-|-9=144 to the 2307 objects of the Northern Slough 

 Catalogue, which increase its numbers to 2451 objects, in which, after 

 subtracting 152 clusters, there remain 2299 nebula;, a number which 

 is not, however, very strictly limited to the latitude of Slough. When 

 numerical relations are to be given in the topography of the firmament 

 of both hemispheres, the author feels that although Ihch data are from 

 their nature variable, owing to the differences in the epochs and the 

 advances of observation, he is bound to have regard to their accuracy. 

 In a sketch of the Cosmos, it must be endeavored to delineate the con- 

 dition of science appertaining to a definite epoch. 



t Sir John Herschel says, in his Observations at the Cape, p. 134, 

 " There are between 300 and 400 nebula of Sir William Herschel's Cat- 

 alogue still unobserved by me ; for the most part, very faint objects." 



