76 THE NEBULA IN ANDROMEDA. 



Marius in the Preface to his Mundus Jovialis. It was then visible 

 to the naked eye, and appeared through the telescope to be com- 

 posed of rays of light (radii albicantes), increasing in brightness as 

 they approached the centre, which was marked by a dull, pale 

 light, — " in centro est lumen obtusum et pallidum." Its diameter 

 was a quarter of a degree, and it resembled the light of a candle, 

 at some distance, shining through horn. Its appearance is also 

 compared to that of the comet observed by Tycho Brahe in 1586.* 

 From some of his remarks, it seems that this author regarded the 

 nebula as an object of extraordinary interest ; and he expresses 

 his astonishment at its having been unnoticed by Tycho when ob- 

 serving the stars in its neighbourhood. 



No further intimation of its having been seen is to be found 

 until 1664. In that year, the appearance of a comet having 

 directed the attention of astronomers to the region in the vicinity 

 of the nebula, it was again discovered, and has not since been 

 lost sight of. 



In the treatise of Ismael Bouillaud before referred to, which was 

 published in 1667, the author maintains, from the fact of its not 

 having been recorded either by Hipparchus, Tycho, or Bayer, 

 as well as from what he had himself observed, that this nebula 

 is subject to periodical variations in brightness ; an opinion which 

 was maintained by many during the succeeding century. 



In 1740, Cassini defines its figure as nearly triangular. Mairan, 

 after stating that the description given by Simon Marius con- 

 formed to what he had himself observed in 1754, asserts that it 

 is subject to changes. The same views are supported by Le 

 Gentil in a memoir, Siir les Etoiles Nebuleuses. From a careful 



• As there was no comet ia 1586, that of 1535 is perhaps intended. 



