66 



Mr T. H. Safford on the Observed Motions 



dition of these four q"uantities, whicli I have determined 

 by least squares, enables us to state with a certain degree of 

 accuracy the angle of position of the centre of gravity with 

 respect to the visible mass, and thus the angle of position 

 of the supposed invisible companion. 



Closely following the actual publication * of this memoir, 

 came the discovery f of the companion by Mr Clark. The 

 question at once arose, whether this were the disturbing 

 body ; the evidence bearing upon this appeared very note- 

 worthy. In the first place, the angle of position agreed 

 (within the uncertainty of observation) with that computed 

 for the disturbing body, assuming my investigation % as the 

 basis. The following table shows the relation for 1862 

 between computation and observation. To my own com- 

 putation I have added the similar one of Auwers, published 

 afterwards. § 



Computed by Auwers, 1862-1 97-3 



Safford, 1862-1 83-8 f (^^'f^ 



" ' \ tion 1-4) 



Observed by Boiicl,|| 1862-2 84-6 



„ Chacornac5 1862-2 84-6 



Lassell,** 1862-3 83 8 



Kutherfurd,ttl862-2 85*0 



The difference between Dr Auwers's theoretical investi- 

 gation and my own is perhaps not larger than the uncer- 

 tainty of all the series of observations on Sirius would ex- 

 plain ; as I have before stated, the amount of deviation from 

 which the angle of position was computed is very small. 



But that the companion of Sirius may produce the dis- 

 turbances, it — the faint object barely visible in the largest 

 class of telescopes — must have a mass nearly tivo-thirdsihdX 



* The number bears date Dec. 20, 1861 ; my own communication, Sept. 

 20th. 



t Jan. 31, 1862. First announced by Professor Bond, in No. 1353 of the 

 Astronomische Nachrichten. 



X This fact was stated by Professor Bond (American Journal of Science for 

 March 1862, p, 287). 



§ Astronomische Nachrichten, No. 1371. It is proper for me here to ex- 

 press my sense of the courtesy with which Dr Auwers admitted my priority 

 in the matter. 



II Astr. Nachr., No. 1374. ^ Ibid. No. 1355. ** Ibid. No. 1360. 



tt American Journal of Science, May 1863, p. 407. 



