695 



The corrections to be apitlied diflfer not much, tiierelbre, from 

 those in the first case. 



As the components of tiie |)arallactic motion are thus found to 

 require appreciable corrections, those found above for tlie precession 

 ai'e no longer Cfuite correct, but tlieir errors are of the same order 

 as other unavoidable inaccuracies in the calculation. 



The result of our research is thus to show tiuit in researclies concern- 

 ing precession and systematic pro|)er motions it is necessary to take 

 into account the dependence of the mean distance upon the galactic 

 latitude: its influence upon both the precessional constant, and the 

 parallactic prop, motion cannot be neglected. 



By taking this influence into account it is possible to bring into 

 fair agreement Newcomb's results for the pi'ecessional constant found 

 from ohservations of R.A. and from those of Decl. For the present, 

 therefore, it is not necessary to follow Hough and Halm, who 

 proceed from a new definition of the precession, by which this is 

 not to be determined with reference to the whole of the stars, but 

 with reference to the mean of the two star streams regarded as 

 of different strength in different parts of the sky: a method wiiich, 

 moreover, as it would appear, involves great difficulties. 



This, of course, does not mean that we can now ixdy u|)on the 

 precession, determined i-elafively to a large complex of stars, giving 

 us the true mechanical precession. To throw more light upon this 

 subject many more extensive researclies will be necessary, in which 

 attention must also be paid to general rotations possif)ly occurring 

 in our system of stars, as first proposed by Sch()NKK,[,d. it seemed 

 prematui'e to include terms of this kind in our present calculations. 



45 



Proceedings Royal Acad. Amsterdam. Vol. XVIII 



