[plaskett] THE SPECTROSCOPIC BINARY THETA 2 TAURI 



161 



accurate period and more consistent and homogeneous elements to be 

 determined. 



Further, the question of a second spectrum shown by two of the 

 Yerkes, and also possibly on some Ottawa plates, should if possible 

 be settled. 



The first series of additional plates in October 1912 was, through 

 an oversight, unfortunately taken at the wrong time and it was not 

 until January 1914 that plates at the proper epoch were obtained. 



When these measures were combined with the earlier ones it was 

 at once seen that the previous period „of 140-50 days obtained from 

 comparison of the Ottawa and earlier observations was not exact but 

 that it would have to be increased about 0-2 days. Observations 7 

 periods apart at approximately the same place on the very steep de- 

 scending branch enabled the period to be determined quite accurately 

 as 140-70 days. 



With this period all the observations were combined into 18 

 normal places, each plate being arbitrarily weighted according io its 

 general quality and the number of lines measured. The weighted 

 velocities and phases of these normal places are given in the ac- 

 companying table, the initial epoch T being taken as Julian Day 

 2,418,000. 



The number and positions of these normal places were so chosen, 

 and at the same time the extreme range of phase in any one of them 

 was relatively so small, that they satisfactorily represent all the ob- 

 servations. 



Their weights are submultiples of the sums of the weights of the 

 plates therein, so taken for convenience of the least squares solutions 

 that the maximum weight is unity. The residuals are those deter- 

 mined from the final elements. 



Normal Places. 



When the normal places were plotted on cross section paper 

 preliminary elements suiting the velocity curve fairly well were, with 



