86 



The Rev. H. Lloyd on the Results of Observations made at the 



Annual and Secular Variations. 



14. The mean yearly values of the declination, for the seven years from 

 1840 to 1846, inclusive, are given in the following Table ; the deviation of the 

 north pole of the magnet from the astronomical meridian being measured from 

 the north eastward. The third column of the Table contains the differences of 

 the declination in the successive years, or the yearly amounts of the secular 

 change. 



Table VIII. Mean Yearly Valdes of the Declination, for the years 1840-46. 



If n denote the number of years reckoned from any epoch. Do the declina- 

 nation at that epoch, and e the change from year to year, the actual declination, 

 D„, will be given by the formula 



D„- Do + ne, 



on the supposition that the change of declination is proportional to the time. 

 But the middle of the year 1840 being taken as the epoch, the values of i)„, 

 corresponding to 7i = 0, 1, 2 . . . 6, are given in the preceding Table ; so that 

 we have seven equations for the determination of Do and e. Combining these 

 equations by the method of least squares, we obtain 



A = 332" 30'.30 ; e = + 6'-060. 

 Consequently the north end of the magnet moves to the east from year to year, 

 and the westerly dechuation therefore diminishes, by 6'-06 annually, in its mean 

 quantity. The amount (as will be seen from the Table) varies considerably in 

 different years. 



Subducting 3'-03 from the value of Do given above, the mean declination 



