4 M. Arago on Double Stars, 



merous. The catalogue of M. Struve, for example, does not in- 

 clude above 52 triple stars within the limits of the scale of an- 

 gular distances which compose the four classes of double stars 

 of Herschel. Of this number we may cite ? of the Crab, and 

 I of the Balance, in both of which the component stars are all 

 three sufficiently brilliant. 



The two several stars of which the double star is composed, 

 have, in general, very different intensities. It even very often 

 happens that they are remarkable for a distinct difference of co- 

 lour. Often the brightest of the two is of a reddish or yellow- 

 ish colour; and more frequently still, the other is of a greenish 

 or bluish shade. We shall arrange in the following table the 

 names of a certain number of double stars which e?fhibit differ- 

 ences of colour, with the purpose of shewing that this kind 

 of star is by no means rare, and also because they furnish to the 

 curious, one of the most interesting subjects of examination. The 

 observations respecting the stars of the southern hemisphere 

 have been derived from the labours of Mr Dunlop, the astrono- 

 mer at Port-Jackson and New Holland ; the others are derived 

 from the catalogues of Herschel and South. 



The 35th* of the Fishes. Larger star white ; smaller blue. 



... X of Aries. white; ... blue. 



... 13th of the Whale. yellow; ... blue. 



... 26th of the Whale. white; ... greenish blue. 



... y of Andromeda. ...... orange; ... emerald green. 



... 59th of Andromeda. Both are bluish ; nearly equal in size. 



... 32d of Eridanus. Greater star a straw colour ; lesser blue. 



... *i of Perseus. , red; ... dull blue. 



... e of Perseus. white; ... bluish. 



... ^ of the Bull. red; ... bluish. 



... 1 8t of the Camel-leopard. yellow ; .^> -y^^^ .^\ .blue. 



... a; of the Charioteer. ^^ fwv granite colour ; ... blue. 



... 62d of Eridanus. ''^^^' '^±*. .':*'" white ; ... blue. 



... /3 of Orion. .,..«,, white; ... bluish. 



... ^ of Orion. white; ... purple. 



... ^ of Orion. yellowish; ... bluish. 



... 8th of the Unicorn. yellow; ... purple. 



♦ It may be useful to give here the signification of the cyphers and of the letters which are era- 

 ployed in distinguishing the stars. 



When Bayer, in 1603, published his Celestial Charts, he affixed In each constellation a letter to 

 every star. The first letter of the Greek alphabet a was placed near the most brilliant star of the 

 ronntellation i the second, /3, at the next most brilliant ; and so on to the last letter o). The Greek 

 alphabet being thus exhausted, the letters of the Roman alphabet, a, b, c, and always in the same 

 order, were next employed. More lately, the number of the stars of all the constellations having 

 been so prodigiously increased by telescopic observations, we are obliged to place them in the cata- 

 logua with a common numeral. The numbers employed in this article, where nothing to the 

 contrary is specified, are those of the old catalogue of Flamsteed, well known under the name of 

 the British Catalogue. 



