236 Praesepe Group; Measurement and Reduction 



Star. 



Epoch. 





Equinox of 1890.0. 



4 



1891.52 



8 h 3i n 



1 28.425, 



+i9°38'59 // -83 



5 



•37 



32 



02.388 



20 35 27 .75 



15 



•55 



33 



23.462 



20 09 55 .52 



40 



.89 



35 



OO.607 



19 39 04 .03 



44 



.89 



35 



33-447 



20 33 03 .40 



Giving these observations the weight ^, and those at Berlin the 

 weight unit} 7 , as was done by Professor Schur, we get finally : 



Star. 



Epoch. 





Equinox of 1890 0. 



4 



1890.58 



8 h 3i J 



"28.440, 



+19 39W.45 



5 



.72 



32 



02.366 



20 35 28 .26 



15 



•53 



33 



23-463 



20 09 55 .42 



40 



.86 



35 



00.582 



19 39 04 .27 



44 



.67 



35 



33-425 



20 33 03 .31 



As the epochs of these observations are from thirteen to twenty 

 years later than the dates of our plates, it is necessary to apply 

 proper motions, for which the following values have been 

 adopted : 



4 



— o. s oo54 



+o // .oo7 



5 



— 0. 0005 



+0 .038 



15 



— 0. 0049 



+0 .017 



40 



— 0. 0040 



+0 .Oil 



44 



— 0. 0044 



+0 .015 



These are the values given by Professor Schur in his catalogue 

 of the group, but they are not derived directly from a comparison 

 of his places with those of Winnecke. Systematic corrections 

 have been added to make the proper motion of the group as a 

 whole conform with observations by Bradley and by Tobias 

 Mayer ; these corrections are : 



— 0/0003 +o // .o39. 



The necessity for such a large correction in declination is ac- 

 counted for by Professor Schur, by assuming that either in the 

 Bonn or in the Gottingen observations, or perhaps in both, the 

 declination of the group as a whole was incorrectly determined ; 

 we shall have occasion to refer to this circumstance later. 



The plates were taken at practically only two dates, 1870.3 and 

 I 877-3 5 a PPtyi n g the corresponding proper motions to the mer- 

 idian observations and reducing them to the equinox of 1875.0, 

 we get : 



