Ball — Researches on Annual Parallax. 363 



observation are, " snow and severe frost; low and hazy, but tolerably 

 steady." On the next night of observation, December 6th, the number 

 of observations was complete, and they were fairly accordant : the 

 notes at the time record, " good definition; thaw; occasional clouds :" 

 the residual on this occasion is - 0""895. It will be noticed that these 

 observations occur at dates Avhen the parallax produces but very little 

 effect, the coefficient being + -2536 on the first occasion, and + "2801 

 on the second. From these we obtain 



x = + 0"-0185 ± 0"-14, 

 a;'= + 0"-0076 ± 0"-27, 

 OT = -0"-1371 ± 0"-ll, 

 K = + 0"-1420 ± 0"-18. 



The sum of the squares of the absolute terms of the equations is 

 + 4"3105, and the sum of the squares of the residuals is + 4"1077, from 

 whence the probable error in an arc of one complete observation of the 

 position angle is 



± 0"-263 



If we combine the two values of the parallax, making due allow- 

 ance for the weights, we obtain, as the final result of this series of 

 observations, 



77 = - 0"-045 ± 0-070. 



If this result were to be strictly interpreted, it would mean that 

 the comparison star was actually the more distant of the two. Observ- 

 ing, however, that the probable error is greater than the parallax 

 itself, it would seem unsafe to draw any conclusion from these obser- 

 vations, save that the difference between the parallaxes of P in 242 

 and BD + 37° 877 is too small to be measured with accuracy. 



Geoombeidge 1618. 



This star is No. 89 of Argelander's list of stars, with large proper mo- 

 tion (Bonn, Ohs., vol. vii. p. 69). It is + 50°, 1725 in ih.Qj)uchnuste- 

 rung, where its magnitude is given as 6'8. The position of the star 

 at the epoch 1878-0 is found from meridian observations at Washington 

 in 1871, andEadcliffe observations in 1859, to beE. A. = lO'^ 3-" 53^-73, 

 8 = 50° 4' 13"- 9, allowance having been made for the proper motions. 



According to Argelander {I. c. p. 110) the proper motion in E. A. is 

 - 0'-1390, and in Decl. - 0"-501. This corresponds to an arcual proper 

 motion of l"-429 per annum, the position angle being 249° 29', i. e., 

 this is the position angle of the place of the star next year from the 

 present place. 



The distance and position of the adjacent star + 50°, 1724 (8-8 

 mag.) has been measured with the view of ascertaining the parallax 



R. I. A. PROC, SEE. II. VOL. III. — SCIENCE. 2 G 



