154 



.EIGHTH REPORT — 1838. 



termined by horizontal vibrations, — namely, eighteen stations 

 by Captain Ross, exclusive of those which have served to ex- 

 amine the magnetism of the cylinder; two stations by Mr. 

 Lloyd; and seven by Major Sabine, — we obtain the follow- 

 ing values : 0;= +'000064; y = --000069; M = -47°14^; 

 r =-000094. The mean geographical position is 52° 43' N., 

 and ^^ 18' W. 



If we now collect in one view the several values of u and r 

 which have been obtained from the intensity observations in 

 England, we have as follows : 



Table LIV. 



If we regarded the several values of u and r in Table 

 LIV., as entitled to weight proportioned to the number of 

 stations of which each is the representative, we should assign 

 a prepondei'ance to the values obtained by the horizontal vi- 

 brations, which the circumstances of the observations from 

 which they are derived would scarcely justify. To give them 

 exactly their just weight, would require a lengthened investiga- 

 tion of the respective probable errors, not only of the two me- 

 thods, but of the horizontal method under some disadvantages, 

 as shown in page 143. The occasion would not justify the ex- 

 penditure of the necessary time and labour ; and I have assign- 

 ed the arbitrary value of 18 to the horizontal deductions from 

 the twenty-seven stations ; making, in this particular instance, 

 three horizontal determinations equivalent to two statical. Thus 

 weighted, we obtain — 50° 48' and -000086 as the mean values 

 of u and r derived from the English series, corresponding to 

 the central geographical position in 52° 48' N. lat., and 2° 07 

 W. long. 



