OF ARTS AND SCIENCES: MAY 26, 1863. 143 



Mr. SafFord presented the following paper : — 



On the Observed Motions of the Companion of Sirins. By 

 T. H. Safford, Assistant at the Observatory of Harvard 

 College. 



It is well known to astronomers that the motions of the bright star 

 Sirius indicated the presence of a disturbing body, before the discovery 

 of a companion by Mr. Alvan Clark. It was shown by Bessel,* that 

 there were irregularities in the motion of this star in right ascension 

 which were only to be explained by the presence of an unseen com- 

 panion, unless, indeed, we might permit ourselves to doubt the univer- 

 sality of the law of gravitation. C. A. F. Peters,t some years later, 

 computed such of the elements of the motion of Sirius around the 

 centre of gravity of the system as could be deduced from the motions 

 in right ascension ; and Schubert % pointed out that there was some 

 reason to believe that the motion in declination also was irregular, 

 though he seems to have fallen into the error of supposing that the 

 motions in right ascension and declination were not completed in the 

 same period. 



Afterwards M. Laugier,§ of the French Institute, represented the 

 observations of Sirius in declination from 1690 to 1852 by a formula of 

 interpolation which I fear we must consider erroneous. Laugier gives 

 a certain weight to Flamsteed's position from the Historia Gcelestis 

 Britannica, which is known to have been reduced (and probably from 

 a single observation), without regard to aberration or nutation ; so that 

 it cannot be depended upon within 15", while the real irregularities 

 of Sirius's motion in declination are less than 2". 



Calandrelli,'! Director of the Pontifical Observatory ** at Eome, has 

 in several places insisted that the Greenwich Twelve-Year Catalogue 

 was in error by about 3" for the date 1845. This, however, was shown 

 by Main ft to be contradicted by the several years' work ; and I pre- 



* Astronoraische Nachrichten, Nos. 514, 515, 516. 

 t Ibid., Nos. 745, 746, 747. 

 X Astronomical Journal, Vol. I. p. 1 54. 

 § Astronomische Nachrichten, No. 1142. 



\ Atti deir Accademia Pontificia de' Nuovi Lincei, 5 Aprile, 1853, p. 316, and 

 elsewhere. 



** This is not to be confounded with the observatory of the Collegio Eomano. 

 ft Monthly Notices of the Royal Astronomical Society, Vol. XX. p 202. 



