BINARY STAR a CENTAURI. 447 



fessor Henderson's parallax ; for, during the whole year, there was not a single 

 day when, if the larger star was seen at aU, the smaller one was not abundantly 

 visible also ; and during that part of the year when they transited the meridian 

 by daylight, they were even then invariably seen with the mural circle telescope, 

 whatever the state of the atmosphere, unless actual clouds intervened. But that 

 the smaller star was never in ages past as low as the fourth magnitude, the mar- 

 vellous change which has occurred in the case of n Argus in our own times, would 

 render a most hazardous assertion. 



A proper motion of the large amount of 3-58" is participated in by both the 

 stars, a fact which pretty clearly proves a physical connection between them ; for 

 while they are now very nearly in the position they were in 100 years ago, when 

 observed by the Abbe Lacaille, they would have separated by this time upwards 

 of five minutes, if one only was pursuing this anomalous path amongst the rest 

 of the stars. 



The first person to remark on this physical connection was Professor Hender- 

 son, who, in the concluding pai-agraph of his memoir on the parallax, says, 



" The two stars appear to be approaching each other. The earliest observa- 

 tions of a Centauri made with a telescope which I have found, are those of 

 Richer at Cayenne in 1673, but neither he nor H alley, who observed it at St 

 Helena in 1677, mentions it as being double. Their telescopes were of course 

 anachromatic, and probably not of much power. Feulle'e appears to have been 

 the first person who observed the star to be double, as he mentions in the journal 

 of his voyage in South America in July 1709. La Cond amine next observed the 

 star during the scientific expedition to Peru for measuring an arc of the meridian." 

 But neither of them made any observations of real service in determining the na- 

 tm'e of the physical connection of the two stars. " From Lacaille's observations 

 in ] 751-2, the distance of the two stars appears to have been then 22-5 ". Mas- 

 KELYNE, who observed them at St Helena in 1761, says {Philosophical Transactions, 

 1764, p. 383), The bright star in the foot of the Centaur, marked a in the cata- 

 logues, when viewed through a telescope, becomes divided into two stars, one of 

 which is about the second and the other the fourth magnitude. They were both ob- 

 served by the Abbe De Lacaille. I found their distance by the divided object- 

 glass micrometer, fitted to the reflecting telescope, to be 15" or 16". I have not found 

 any observations," continues Professor Henderson, " of the distance of the two 

 stars made between 1761, and the institution of the Paramatta Observatory : there, 

 in the end of 1825 or the beginning of 1826, the distance was observed to be 23" 

 {Memoirs of Astrmwmical Society, Vol. iii., p. 265), since which time it has been 

 decreasing at the rate of more than half a second per armum. The angle of posi- 

 tion scarcely appears to have changed since Lacaille's time, whence it may be 

 inferred, that the relative orbit is seen projected into a straight line or very excen- 

 tric ellipse ; that an apparent maximum of distance was attained in the end of 



