THE SUN'S MOTION IN SPACE. 183 



1865, and the result is for the mean of those dates, viz., for the 

 1810-0. 



(87) Stumpe, 1890. — In 1890 Stumpe undertook an investiga- 

 tion of the motion of the solar system having regard to the 

 possibility of some general law in the motus peculiaris of fixed 

 stars, existing. 1 All stars used in the investigation were reduced 

 by Struve's Precession-constant to the equinox of 1855 0, the right 

 ascension upon the Fundamental system of Newcomb, the declina- 

 tions on Boss's system. The material for the determination was 

 fully discussed and carefully corrected. Drawing attention to the 

 fact that in previous determinations it has always been assumed 

 that the motus peculiaris* of the stars is subject to no regular law 

 — such as was contemplated in J. Herschel's hypothesis of a 

 rotation in the plane of the Galaxy — Stumpe introduced into his 

 equations, for the motion of the solar system, which in other 

 respects were identical with Airy's, terms denoting the galacto- 

 centric right ascension, declination, and distance of the sun, and 

 the right ascension of the ascending node of the Milky-way and 

 the inclination of its plane and the equator. The stars were 

 divided into four groups according to the magnitude of the proper 

 motions, with the result shewn in the following table : 



&rou 



p. P.M. No. of Stars. 



R.A. 



D. 



R. 



I. 



0-16 to 0-32 



551 



287-4 



+ 42 ? 



: i40 



II. 



0-32 064 



340 



279-7 



40-5 



0-295 



III. 



0-64 1-28 



105 



287-9 



32-1 



0-608 



IV. 



"I ,OQ and upward 



Total 



58 



285-2 

 i 285-0 



30-4 



2-057 





1054 Meai 



36-2 0] 



r about 39° taking account 

 of number of stars. 



R denoting the ratio of the annual motion to the mean distance 

 of the group. Thus it would appear that the distance of the stars 

 is in general reciprocally proportional to their proper motion. 



1 Untersuchungen uber die Bewegung des Sonnensysteins. — Astr. Nach. 

 Bd. cxxv.j pp. 385 - 426, 1890. See also The Observatory, Vol. xiv., pp. 

 68-69. 



. 2 The motus 'peculiaris is the absolute motion of the star itself, while 

 the ' proper motion ' is the apparent motion arising from the combined 

 effect of the motus peculiaris of the star, and that of the solar system . 



