Dreyer — On Astronomical Transit Observations. 



519 



by Trettenero, with the catalogues of Schjellerup and Bessel. He 

 found by dividing the stars according to the magnitude :"^' — 



Magn. 



Schj.-Tr. 



Stars. 



A'«. 



gm 



+ 0'-023 



14 



- 0^-013 



7 



+ -031 



35 



+ -017 



7-8 



+ -089 



23 



- -022 



8 



+ -084 



68 



+ -002 



8-9 



+ -lOo 



74 



-000 



9 



4- 0-124 



120 



-000 



The increase of the difference with the decrease of the brightness 

 of the stars seems beyond doubt. The last column contains the 

 deviations of the differences from the formula : — 



Schj.-Tr. = + 0^-010 + 0^-038 [Magn. - 6™-0]. 



The comparison between the Padua zones and those of Bessel gave 

 a similar result, which, however, is more uncertain than the above 

 one, owing to constant errors in some of Bessel's zones, uncertainty 

 of proper motions, &c. Argelander informs us also that the third 

 Padua catalogue has been found by himself to contain a similar devia- 

 tion of the faint stars. 



It seems, therefore, that Trettenero really observed faint stars 

 earlier than bright ones, probably because his attention while observ- 

 ing the former was more concentrated in the work of the eye, or 

 because he regularly first heard the beats of the clock, and then 

 saw, while he observed bright stars in the reverse way. Argelander 

 has already, in Yol. YI. of the Bonn Observations (p. 12), suspected 

 that a fault in his own R. A.s might arise in this way, and he has 

 later examined his own observations of variable stars, in order to find 

 whether any certain influence of the magnitude on the R. A. would 

 appear from these. The result was, that Argelander seemed to 

 observe stars down to 9*1 magnitude in the same way, but stars of the 

 magnitude 9*2, and still more those of magnitude 9"3, a little earlier ; 

 but that the en'or for the latter could hardly amount to more than 

 0^-15. Por stars below the 9-3 magnitude, the accidental errors 

 seemed to amount to more than the constant one, so that the latter 

 could not appear distinctly.! 



As observations of variable stars in their different phases of bright- 

 ness are included in the programme of the zone observations, at present 

 undertaken by different observatories, under the direction of the Inter- 

 national Astronomical Association, we shall, probably, soon possess. 



* Vierteljahrsschiift, vii., p. 19. 



t Astron. Naclirichtcn, Ixxiv., p. 268. 



