204 G. H. KNIBBS. 



(122) Kapteyn, 1898 (April)— In April 1898 Kapteyn repub- 

 lished a number of his smaller papers previously referred to, 

 contributed to the Royal Academy of Sciences in Amsterdam, 

 concerning the velocity of the solar and stellar motions in space, 

 in a more developed form in the Astronomische Nachrichten. 1 

 This last treatise was divided into four heads : — 



(a) The mean velocity of the stars compared with the velocity 



in space of the solar-system. 



(b) The velocity of the solar-system in space. 



(c) The mean velocity of stars of different magnitudes. 



(d) The influence of an error in the assumed constant of pre- 



cession. 



In (a) Kapteyn developed the fundamental equations of his 

 investigation, and discussed the definitions and assumptions, 

 involved in their application. He criticised the legitimacy of 

 Ristenpart's deduction as to variation of velocity with increase of 

 distance from the sun. Accepting for the position of the apex 

 of solar motion the values for 1875 



R.A. = 276°, D.= +34° 

 and dividing the stars according to their photometric magnitude, 

 and also according to their spectral type, for the determination of 

 which Draper's catalogue was used, he obtained the following 

 results : — 



No. of Stars. 

 60\ 



Phot. Mag. 

 0-3-5 



Spectr. type. 

 II. 



[n]/V 

 1-17) 



0'78 [ 1.35 



72 



285 



0-3-5 



I. and unknown 



153 J 





3-6-45 



II. 



1-69J 



335 





4-6-5-5 



II. 



2-04 



488 





5-6-6-5 



11. 



1-30 



162 





3-6-4-5 



I. and unknown 



1-36 



254 





6-6-7-5 



all 



1-95 



356 





4-6 -5-5 



I. and unknown 



1-41 



705 





5-6-6-5 



I. and unknown 



1-48 



Total 2,585 







Mean 



1-51 



1 Die mittlere Geschwindigkeit der Sterne, die Quantitat der Sonnen- 

 bewegungund die mittlere Parallaxe der Sterne von verschiedener Grosse. 

 — Astr. Naoh., Bd. cxlvi., pp. 97 - 114, 1898. 



