ASTRONOMY. 371 



d = +37° 27'. 1, and p.= 10.85 radii of the earth's orbit, fi is the linear 

 motion of the solar system. 



Dr. Ball's 80 southern proper motions give from the R. A., A = 273° 

 4G'.G; and from the Declinations, A = 244° 4'.1, d = +170 27'.1 and 

 i>. = 4.59 radii. These results differ so much from each other, that the 

 data haveheen combined anew by introducing the parallax of each star 

 in such a way a* to diminish the effect of proper motions much larger than 

 the average. With the new equations the results are from Argelander 

 in E. A., A = 275o 15'.2, in Dccl. A = 2SS° 31'.3, D = +41° 2'.4, and 

 ;j. = 10.61 radii. Ball's 80 stars give in E. A., A = 2S1° 2'.S, and in Decl. 

 A = 240° 24'.5, d = +11° 54'.3, and fi = 7.83 radii. This transformation, 

 then, has produced only a greater accordance in the values of the linear 

 motion of the system. Both solutions show that the solar motion 

 alone is not sufficient to account for the proper motions of the stars 

 employed. 



The next step in the process is to see if there is not some further 

 systematic motion of the stars which will account for their proper 

 motions. 



The first trial is to see if a common motion of all the stars parallel to 

 the plane of the Milky Way will suffice. 



The position and motion of each star have been referred to that great 

 circle which best represents the Milky Way. Those stars between 

 -f- 30° and — 30° galactic latitude whose proper motions are less than 

 0".25 have been separately considered. They are 10G in number. From 

 their proper motions in E. A. it follows A = 294° 2S / .7. From those in 

 Decl. A =275o 47'.9, D = + 31° 52'.1, and ^=9.79 radii of the earth's 

 orbit. 



If die is the systematic motion of the 10G stars paralled to the plane 

 of the Milky Way, there results from the proper motions in E. A., div = 

 + 0.05G45 ± 0.01288, and from those in Decl., dw = + 0-02385 ± 0.01464. 

 These last values of dw have a sufficient agreement to give a great in- 

 terest to this research and to those which Dr. Eancken intends to carry 

 out using a greater number of stars. 



FIXED STAES. 



The constant of aberration. — M. Magnus Nyren has published, in the 

 Memoirs of the St. Petersburg Academy, a valuable paper on the deter- 

 mination of this important astronomical constant. Various determina- 

 tions of the value of the constant of aberration made by different observ- 

 ers, with different instruments and by different methods, have gradually 

 led astronomers to consider that there is a probobility, or, at all events, 

 a possibility, that W. Struve's value, notwithstanding the small prob- 

 able error found for it, and notwithstanding the great care and skill be- 

 stowed on the observations and on their reduction, may be several 

 hundredths of a second too small. M. Nyren points out two possible 



