Double Stars. — Occultations. 301 



thousands of similar objects, it possesses some interest both as 

 the point of departure from which the parallax of the great star 

 is measured, and as a well-known test for instruments of a 

 moderate size. It is evident that a certain proportion of light 

 is requisite. I believe it might be seen with 3i inches of real 

 excellence. I have caught it, but only in very fine weather, 

 with 3£j ; four inches ought to hold it pretty steadily in a 

 clear atmosphere. Increase of power is serviceable, as tend- 

 ing to draw away that little point from the dazzling blaze, and 

 to place it on a quieter and darker background ; and thus Sir 

 W. Herschel found it invisible with 227, but visible with the 

 same aperture with 460 ; and when Kitchener could not see it 

 in his 5 -feet achromatic with 250, he perceived it easily with 

 350 and 450. In my present instrument I see it with 55. 

 What must be the light-grasping capacity of Sir John HerscheFs 

 18j-inch speculum we may guess from his statement, that he 

 has well seen and measured it in broad twilight, just after 

 sunset, and with a moon ! 



The next star to Wega (at the present season above it) is a 

 peculiarly beautiful and remarkable object, commonly called 

 e Lyrce, though more correctly by a combination of Bayer's 

 alphabetical with Flamsteed's numerical designation — ■ 



47. e ! 4 and e 2 5 Lyrce. This is a quadruple, or more pro_ 

 perly a double-double star. First of all we have a pair 3' 27" 

 apart, just far enough to be separately distinguished by a very 

 keen sight. Herschel I. once mentions having so seen it; 

 Bessel could divide it at thirteen years of age, and I have mot 

 with two modern instances in England ; but to the generality of 

 eyes it will probably appear (as it does to my own) what Smyth 

 calls it, " an irregular looking star." This pair, of course, is 

 widely separated in the telescope, while at the same time it is 

 perceived that each of the components is again closely double — 

 a beautiful combination. The data of e 1 are 3" 2, 20°*6, 5 and Q\, 

 yellow and ruddy : those of e l are 2"'6, 150°*9, 5 and 5|, both 

 white. Each pair is believed to be in slow motion, e 1 the most 

 northerly, with a period of about 2000 years, the other as fast 

 again : while both may possibly revolve round a common centre of 

 gravity in years innumerable by the skill of man. Struve differs 

 from other observers (except Dembowski) in ascribing a bluish 

 tint to the smaller star of e 1 ; this peculiarity attaches to the 

 observations of five years, and is the more remarkable as the 

 colours of this great astronomer are usually accordant with those 

 of other standard authorities. He also suspects variable light 

 in one of the stars of e\ An aperture of 2£ inches, perhaps 

 even a little less, is sufficient, if really good, for these beautiful, 

 pairs. With large instruments three more stars are added to 

 the group; one, which Dawes calls 9*5 mag. is comparatively 



