374 Double Stars. 



This is a Persei, and it forms the starting-point of a remarkable 

 sequence of 4 large stars, at nearly equal and considerable dis- 

 tances, ranging in a great curve towards the right beneath 

 Cassiopea, without the intervention of any remarkable object. 

 Beginning with a Persei, the others are <y, /3, and a Andromedce, 

 often called respectively Alamalc, Mirach, and Alpherat. We 

 must look at the first of these three. 



64. 7 Andromedce. 11". 61°"6. 3|and5|-. Deep yellow 

 and sea-green. This, since its discovery by Christian Mayer in 

 1778, has been known as one of the most brilliant and beautiful 

 instances of contrasted colour, as well as one of the easiest pairs 

 in the heavens. There is no evidence of orbital revolution, but 

 a fresh degree of interest has been attached to this object since 

 Struve, senior, discovered with the Dorpat achromatic, twenty 

 years ago, that the smaller star was itself an exceedingly close 

 and difficult pair. The distance is given as under 0""5, and it 

 consequently forms a most severe test of defining power. 

 Cookers (of York) beautiful object-glasses of little more than 

 4 inches will elongate it, and Mr. Lockyer, of Wimbledon, 

 has divided it with 6^ inches by the same hand — a great 

 triumph of optical skill. Secchi at Rome actually measures it, 

 and calls it easy I with the Merz achromatic of 9^ inches, and 

 its division is ' ' a broad dark space" with the new equatorial 

 at Greenwich of 12f inches, also from Munich. One of the 

 new silvered glass specula manufactured by Leon Eoucault (a 

 remarkable invention, of which we shall shortly hear more in 

 England) has accomplished the separation with about the same 

 aperture ; but as much has been done by a metallic mirror of 

 9j inches, figured by Lassell. I have repeatedly elongated it 

 with my 5|-inch object-glass. The little discs are of unequal 

 magnitude, the nearer to the great star being the larger. A 

 difference of hue was noted by Secchi in 1856, who calls them 

 subviridis and violacea. The late Sir W. K. Murray, of Och- 

 tertyre, who had a 9-inch telescope by Cooke, discovered 

 independently, in 1857, that they were yellow and blue. 

 Dawes, with an 8-inch Alvan Clark object-glass, made the same 

 observation ; and Jacob, at Madras, with the Lerebours achro- 

 matic of 6^- inches, though unable to divide them, found the 

 larger end of the ivedge yellowish, the other bluish. Few of 

 our readers may hope to verify these details ; yet it may interest 

 them to know, when they gaze upon that minute speck, what 

 other telescopes exhibit there. 



a Andromeda?-, already mentioned, stands at the left-hand 

 upper corner of a rectangle of large stars, so fairly regular that 

 the bottom line is sensibly horizontal, and the right side nearly 

 vertical, when on the meridian. This is the square of Pegasus, 

 marking the E. portion of that wide-spread constellation. At 



