LONGITUDE OF McGILL OBSEEVATORY. 



171 



It will be seen that the final values of AT have been derived from a combination of 

 results (6) and (9). Unless the value of c can be found by the mechanical method, these 

 forms of solution are probably as likely to give the true values of A2' as any that can 

 be chosen. This selection, however, must always be to a certain extent a question of 

 individual judgment. It will not escape attention that the gain in the introduction 

 of weights is very slight. It can only be said that their use seems to jjroduce a little 

 better accordance of the residuals. 



Personal Equation between W. A. Rogers and C. H. McLeod. 



The following values of the personal equation between Professor McLeod and my- 

 self were derived from observations on two nights at Cambridge and on two nights at 

 Montreal. The plan of observation adopted was for one observer to get three sym- 

 metrical tallies, and for the other observer to get the remaining tallies, reversing the 

 order of the tallies for alternate stars. 



The results derived from each star observed are given in the following table : — 



