On the Observed Motions of the Companion of Sirius. 65 



companion, unless, indeed, we might permit ourselves to 

 doubt the universality of the law of gravitation. C. A. F. 

 Peters,* 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 as- 

 cension ; and Schubert f pointed out that there was some 

 reason to believe that the motion in declination a\so was 

 irregular, though he seems to have fallen into the error of 

 supposing that the motions in right ascension and declina- 

 tion were not completed in the same period. 



Afterwards M. Laugier,J of the French Institute, repre- 

 sented 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 CoelestisBritannica," 

 which is known to have been reduced (and probably from 

 a single observation), without regard to aberration or nuta- 

 tion ; so that it cannot be depended upon wdthin 15'', w^hile 

 the real irregularities of Sirius's motion in declination are 

 less than 2". 



Ca]and]'elli5§ Director of the Pontifical Observatory || at 

 Kome, 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 Tf to be 

 contradicted by the several years' work, and I presume most 

 astronomers would agree in considering Calandrelli's argu- 

 ment as irrelevant. 



In No. 28 of Professor Brunnow's valuable " Astrono- 

 mical Notices," I have shown that, in spite of the misap- 

 prehensions to w^hich I have just alluded, the observed 

 motion of Sirius in declination is in fact represented by a 

 formula depending on the previous investigation of Peters, 

 but with four new unknown quantities inserted. The ad- 



* Astronomische Nachrichten, Nos. 745-747. 

 t Astronomical Journal, vol. i. p. 154. 

 X Astronomische Nachrichten, No. 1142. 



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

 and elsewhere. 



II This is not to be confounded with the observatory of the Collegio 

 Romano, 



^ Monthly Notices of the Royal Astronomical Society vol. xx. p. 202. 

 NEW SERIES. VOL. XIX. NO. I. JANUARY 1864. I 



