152 Parallax of 61 2 Cygni, deduced from 



43. From these equations are obtained the following normal 

 equations and values of the unknowns : 



Normal Equations, 

 -f-iio.oooox +129.0300?/ — 19.1300II -(-10.3300 = 

 +215.2083 — 3.9695 +i5-7599 = o 

 +39.4805 — 3.4429=0 



Solution. 



Weights. 

 # = + o // . 0180 ±0^. 0014 25.49 



y = — o .0824 ±0 .0093 54-42 



n = + o .0876 ± o .0123 30.81 



Probable error of one equation = zb o // .o684 

 [vv\ = i // .ioo6 



44. It will be noticed that this difference of parallax between 

 6i x and 61 2 is in very close agreement with the + o' f .o"j2 ± ."028 

 derived from the Rutherfurd measures. Its probable error and 

 the sum of the squares of the residuals when compared with simi- 

 lar quantities* in Wilsing's determination of the parallax of 61 2 

 Cygni would indicate that it has as real an existence in the meas- 

 ures as his own values of the parallax of 61 2 itself; while at the 

 same time bearing testimony to the excellent quality of his meas- 

 ures. 



45. Yet this difference cf parallax does not preclude the possi- 

 bility of orbital motion of either 61 1 or 6i % about a dark com- 

 panion, as has been suggested by Wilsing to account for the sys- 

 tematic irregularity of his measures — a suggestion which the 

 outstanding residuals, after corrections for this difference of paral- 

 lax have been applied to the measures, would in a degree confirm. 

 And yet it is greatly to be regretted that points numbered 1, 2, 3, 

 and 4 of his curvef are determined by only 4, 2, 2, and 2, ex- 

 posures on 2, 1, 1, and 1 plates respectively, in contrast with the 

 other points which are determined by the means of from 11 to 40 

 exposures ; and that the most critical portion of the curve (that 

 from January 15th, 1892, to January 13th, 1893) * s determined by 

 two points only, from 15 and 11 exposures on only 5 and 4 plates 

 respectively. Moreover, for the reasons stated on page 160 of this 

 paper, the testimony of the Pritchard measures, adduced by 



* \yv\ =2.691 ; 2.390 and 1.681 on pages 109, 114 and 120 respectively, 

 Publicationen, etc. 



f Sitzungsberichten, etc., pages 884-5. 



