m 
Porz.—On the Southern Stars and other Celestial Objects. 173 
a Centauri.—R. A. 14hrs. 80min. 47:07sees. Decl. 60° 17’ 53°93". 
Magnitudes, 1-2. The following table will give the position-angles, and the 
distances of the components of this star, for selected epochs during the 
forty-five years which have elapsed since 1834, when it was first accurately 
measured by the greatest of all astronomers, Sir J. Herschel :— 
OBSERVER. Date. Posrrron. DISTANCE. 
Sir J. Herschel = vs e 1834-7 — 17:43” 
Sir J. Herschel 3 si Ex 1834:8 218? 30' — 
Sir J. Herschel e i» Ex 1835-7 219° 80' — 
Sir J. Herschel & e 4 1837-3 220° 42’ — 
ir J. Hersch us vx 1837:4 — 16°12” 
Powell (from Webb) . eg us 1864 5° T 7°85" 
in F. M. G.C 1870-0 17° 19’ 10:73" 
My recent measures .. e ES 1878:7 156? 19' — 
My recent measures .. Pee s 1879-75 183? 8' 4-55" 
With this table as a basis, it wil be found that the major axis of the 
apparent orbit lies nearly in the direction 261? to 2063?, and that the 
greatest elongation north is about 11”, while the greatest elongation south 
is 27". Mr. Powell makes the period between 76 and 77 years. If the 
places of the two stars given by Lacaille (1750) were correct, however, the 
period would be just about 85 years, for the angle of position computed from 
his places of the stars is 218? 44', which a reference to the above table will 
show, was very nearly Sir John Herschel's micrometrically-determined 
position 84-79 years afterward. As, however, the distance obtained by Sir 
John Herschel disagrees very materially with that deduced from Lacaille's 
places of the stars, but little weight is attached to the observation of 1750. 
This magnificent double star is the finest object of the kind in the 
heavens. Besides being a binary star of very short period, every one 
knows that a Centauri is our next neighbour among the stars, and that it 
was the first to give up the secret of its parallax under direct Transit Circle 
observations. The colour of this star is straw-yellow, or sometimes golden- 
yellow, according to the state of the atmosphere. When there is haze, of 
course the smaller star is somewhat more affected by it than the larger. This 
tends to give it a slight brownish tint when the sky is not clear. a Centauri is 
a star of the second class. Its spectrum is very like that of the sun. Even 
the principal dark lines are fine, and they apparently occupy the same rela- 
tive positions as do the well-known lettered lines in the so 
The resemblance between the two spectra is so striking that any one see- 
ing the two spectra for the first time could hardly fail to notice the similarity. 
More dispersive power, however, and the means of accurately determining 
the position of the lines of a Centauri might show that they are not the 
