NEBULiE. 21 



Compared with the slow progress we have hitherto depicted, 

 the knowledge of nebulous spots received a rich accession of 

 facts by the persevering industry of Messier. His catalogue 

 of 1771 contains, after deducting the older nebulae discovered 

 by Lacaille and Mechain, 66 w'hich had not been previously 

 observed. He had the merit of doubling the number of the 

 nebulous spots hitherto enumerated in both hemispheres, al- 

 though his labors were carried on in the ill-supplied Observa- 

 toire de la Marine (Hotel de Clugny).=* 



To these feeble beginnings succeeded the brilliant epochs 

 of the discoveries of William Herschel and his son. The for- 

 mer began, as early as 1779, a regular exploration of the nu- 

 merous nebulous masses with which the heavens are studded. 

 These observations were made with a seven-feet reflector. 

 His colossal forty-feet telescope was completed in 1787; and 

 in the three catalogues! which he published in 1786, 1789, 

 and 1802, he indicated the positions of 2500 nebulae and 

 cluste-^ of stars. Until 1785, or almost as late as 1791, 

 this great observer appears to have been more disposed, like 

 Michell, Cassini, and the present Lord Rosse, to regard the 

 nebulous spots which he was unable to resolve as very remote 

 clusters of stars ; but a prolonged consideration of the subject 

 between 1799 and 1802 led him to adopt the nebular theory, 

 as Halley and Lacaille had done, and even, with Tycho Brahe 

 and Kepler, the theory of a star-formation through the grad- 

 ual condensation of cosmical vapor. The two hypotheses, 

 however, are not necessarily connected. $ The nebulous and 

 stellar clusters observed by Sir WiUiam Herschel were sub- 

 jected by his son to a renewed investigation from 1825 to 

 1833 ; he also enriched the older catalogues with 500 new 

 objects, and published in the Philosophical Tra7isactions for 

 1833 (p. 365-481) a complete catalogue of 2307 nebulae and 

 clusters of stars. This great work contains all that had been 

 discovered in the heavens of Central Europe ; and in the five 

 succeeding years (from 1834-1838) we find Sir John Her- 



Ivii., for 1767, p. 251), " in which we can discover either none, or only 

 a few stars, even with the assistance of the best telescopes, are probably 

 systems that are still more distant than the rest." 



* Messier, in the Mim. de VAcadimie des Sciences, 1771, p. 435, and 

 in the Connaissance des Temps pour 1783 et 1784. The whole catalogue 

 contains 103 objects. 



t Philos. Transact., vols. lxxvi.,lxxix., and xcii. 



X " The nebular hypothesis, as it has been termed, and the theory of 

 sidereal aggregation, stand, in fact, quite independent of each other. "- 

 Sir John Herschel, Oitiiwes of Astronomy, $ 872, p. 599. 



