310 M. Arago on Nebulce. 



state, appeared not less worthy of attention, and presented it- 

 self to minds embued with some philosophy, as a fruitful 

 source of discoveries. 



Historical Sketch of the Discovery of Nebulce. — The first ne- 

 bula of which mention is made in the annals of astronomy, is 

 the nebula oi Andromeda. It was observed by Simon Marius 

 in 1G12. This astronomer compared the light of the nebula 

 of Andromeda to that of a candle seen through a thin plate of 

 horn, and the comparison is not inaccurate. Nearly half a 

 century had elapsed from the time of Marius, when, in the year 

 1656, Huygens observed the large nebula in the constellation 

 Orion. In 1716, Halley, when enumerating the known ne- 

 bulae, found that they amounted only to six : the two already 

 mentioned; one, the discovery of which he ascribes to Abraham 

 Ihle, but which, before 1665, had already been noticed by 

 Hevelius ; it is between the head and the bow of Sagittarius ; 

 the nebula situated in the Centaur, which Halley discovered in 

 the year 1677, while he was working at the catalogue of stars 

 in the southern heavens ; the nebula near the right or northern 

 foot of AntinoiJs, which Kirch observed in 1681 ; finally, a ne- 

 bula, the discovery of which is also due to Halley, situate in 

 the constellation Hercules, on a straight line drawn from ^ to 

 71 of Bayer. 



During his residence at the Cape of Good Hope, Lacaille 

 fixed the position of 14 nebulae, in which his feeble instruments 

 shewed nothing definite ; and that of 14 others, which the 

 same glasses, on the contrary, decomposed into stars. A few 

 years afterwards, the amount of these objects was notably ex- 

 tended. Messier's catalogue, commvmicated to the Academy 

 in 1771, and inserted, with some additions, in the Connaissance 

 des Temps of 1783, contained 68 nebula3, which, with the ad- 

 dition of Lacaille's 28, formed a total of 96. This branch 

 of science made the most rapid progress, as soon as Her- 

 schel brought to its service his powerful instruments, a rare 

 degree of penetration, and indomitable perseverance. In 1786, 

 this learned philosopher published, in the 76th volume of the 

 Philosophical Transactions ^ a catalogue of a thousand nebulae, 

 or masses of stars. Three years afterwards, to the great 

 astonishment of observers, a second catalogue appeai'ed, as ex- 



