Ball — Researches on Annual Parallax. 367 



From these we find the following values : — 

 X =- 0"-3532 ± -133, 

 a;' = + 0"-3222 ± -116, 

 w = + 0"-3196 ± -052, 

 K - - 0"-0422 ± -066. 



The probable error of one observation is + '119. 



The sum of the squares (nn) ~ 2-330. 



The sum of the squares (w) = 1-255. 



These observations are free from the features which appeared to 

 me to be objectionable in the former series. On the other hand, it is 

 to be observed that the corrections to the proper motion and to the an- 

 nual mean distance now attain considerable amounts. This is, I be- 

 lieve, partly due to the choice of an epoch which is more than a year 

 from the mean date of the observations. To examine the plausibility 

 of these corrections I have combined the results of the two series of 

 observations, taking account of their probable errors. I thus find 



X =- 0".1858 + -047, 



a;' = + 0"-1985 ± -060, 



OT = + 0"-3339 ± -036, 



K --0"-1774 ± -044. 



These results do not appear to be at all improbable. A positive 

 correction to the proper motion is indeed indicated by the adopted 

 mean distances at the epochs of 1878 and 1879. These are, respec- 

 tively, 190-7608 and 197-7308. This corresponds to a proper motion 

 in the distance of somewhat over a second per annum, while the 

 assumed proper motion is somewhat less than a second. Nearly half of 

 the value of x' is thus accounted for. 



I believe that these observations render the existence of a parallax 

 of about one-third of a second tolerably certain. It will not, however, 

 be possible to determine the parallax definitively until further investi- 

 gations have been made. Measurements of the position angle of the 

 comparison star from Gr. 1618 are very well adapted for this purpose. 

 Indeed, the parallax has a much larger effect upon the position angle 

 than it has upon the distance. I have made such measurements at the 

 same time as the measurements of distance which are here discussed. 

 These observations are not yet ready for publication. I may, however, 

 say that though some difficulties have been met with, yet the position 

 angle observations, as a whole, tend to confirm the fact that Grr. 1618 

 has a parallax sufficiently large to entitle it to a place among the 

 sun's nearest neighbours. 



