KirkwoocJ.J h'iA [April i>, 



H\ f'YGNI. 



The iinnual ])!iriilla.v of 61 Cygni is *o% ths of a second, whicli cor- 

 responds to a distiince 448,000 times that of the earth from the sun. The 

 magnitudes of the components are o^ and (i ; their distance from cacli other 

 is 45 times the radius of tlie eartli's orbit ; tiieir period, about 500 years ; 

 and tl»e sum of their masses, rather more than one tliird of tlie sun's 

 mass. They liave the same color- -a golden yellow. 



The mass of the larger component of Gl Cygni may be taken at one fifth 

 of the sun's mass. According to the estimate of Sir William llerschel thc- 

 light of an average star of the first magnitude is 50 times that of a star of 

 the fifth, or about 75 times that of the larger ctmiponent of (il Cygni. The 

 intrinsic light of the principal member of Alpha ('entauri being twice 

 that of the sun and 75 times that of A, 01 Cygni, we obtain the following 

 relations : 



Sun. .\. 1)1 ( 'ygni. 



Surface, (densities equal?) 3 1 



Mass 5 1 



Intrinsic light 9A 1. • 



These numbers seem to indicate that 61 C'ygni is farther advanced than 

 the sun in its physical history. 



SiRIUS. 



" It has been long acknowledged, "says Humboldt, " that of all the bright- 

 est luminous fixed stars of heaven, Sirius takes the first and most important 

 place, no less in a chronological point of view, than through its historical 

 association with the earliest development of human civilization in the val- 

 ley of the Nile." The recent discovery of its binary character, together 

 with the determination of its parallax, mass, motion, and constituent ele- 

 ments, have greatly enhanced the interest with which this star is I'egarded 

 l)y the scientific public. From the meridian altitudes of Sirius, as observed 

 by Sir Thomas Maclear, at the Cape of Good Hope during the years 1836 

 and 1837, Dr. Gylden, of Pulkowa, has found its annual parallax tobe i'jV,v 

 ths of a second, which corresponds to a distance 1,008,700 times that 

 of the sun from the earth. The light of this star is therefore 16 years in 

 reaching us. 



The orbit of this binary system has Ix-en computed by Dr. Auwers, who 

 finds the period of revolution to be 4'.) years and 146 days ; the semi-axis 

 major, 37 times the distance of the earth from the sun; and the eccentricity, 

 0.6148, — somewhat greater than that of Fays's comet. The mass of the 

 conipanion is half that of the principal star ; or more accurate]}', the mass 

 of Sirius is 13.76, and that of the telescopic star, 6.71, the mass of the sun 

 being unity. According to the photometrical experiments of Sir John 

 Herschel, the light received from Sirius exceeds that of Alpha (-entauri in 

 the ratio of 25 to 6. Comparing, therefore, tlie distances of the two stars. 

 wc find th(> intrinsic light of Sirius to be 1)3 limes that of Al|)ha Centauri. 



