957 



the catalogues had 1489 stars in common between the above men- 

 tioned declination limits, 1695 obsei-valions of which occur in B. Z. 

 The epochs are 1823.0 and 1895.2, the difference of epoch being 

 therefore 72.2 years. 



2. Reduction of the dijferences KU — B. Z. to a Funilamental 

 system. Determination of the constant zone-errors of B.Z. 



It is well known, that (he separate zones of Bkssei, show in 

 several cases fairly large systematic, usually constant, errors, the 

 determination of which is imperatively necessary in researches 

 as the present one. This determination can be made by comparison 

 of B. Z. with simultaneous observations or with coordinates which 

 have been obtained by interpolation between earlier and later 

 observations. In this case I have used for the purpose coordinates 

 from Auuers-Bradlky, Tobias Maykr's Stern verzeichniss and Argk- 

 lander's Catalogus Aboensis, which between them have almost 

 600 stars in common with B. Z. For tiiese stars the differences 

 Au Br — B. Z., TM — B. Z., and Abo — B.Z. were taken and kept 

 separated according to Bessel's zones. After all differences 

 Abo — B. Z. had been made to correspond to the differences 

 Au Br. - — B. Z. by the addition of the systematic difference 

 Au Br. — Abo (the differences TM — B. Z. do this already), all diffe- 

 rences that were shown to possess the same weight, were simply 

 averaged for each of Bessel's zones, whereby, thus, for each zone a 

 value of the reduction to the system Au Br was found. 



In a numbei' of zones the number of stars that occurred in the 

 catalogues used for comparison proved to be too small for the 

 deduced reduction to Au Br to be regarded as sufficiently accurate. 

 I have compared these zones (by means of stars in common) with as 

 many other zones as possible, the corrections for which had been 

 determined with satisfactory accuracy, in order to find reliable 

 corrections for these zones also. In most cases the result was 

 satisfactory. 



In a few cases it was possible to determine the total zone-errors 

 in ail indirect way, viz. by using the A. G. catalogues Albany and 

 Nicolajew, in such a way that I could make myself free from the 

 systematic changes during the difference of epoch. 



Everything taken together it was possible in almost all cases to 

 deduce a sufficiently reliable final value for the individual zone 

 corrections. In only two cases the .s7/.sA^///^///c reduction A ii Br ^ — B.Z. 

 which I had deduced and calculated for comparison for all zones, 

 had to be taken as total correction. 



67 



[Proceedings Royal Acad. Amsterdam. Vol. XX. 



