MAGNETIC ELEMENTS AT TORONTO. 115 



aereral months occur in which the absolute declination was not deter- 

 mined. In these cases, the approximate annual means given in the 

 table are the averages of the results for the months wherein observa- 

 tions were made, these results being corrected for annual and secular 

 variation. These corrections were determined as follows : The twelva 

 monthly means on the average of the nine years, 1856 to 1864, being 

 in the first instance corrected for secular change, by the application to 

 them of the several multiples of 0'.2606, from +5.5 x O'.2606 in 

 January, to — 5.5 X 0'.26O6 in December, were then subtracted severally 

 from the mean declination 2° 10'. 04, thus yielding remainders which 

 have been adopted as the monthly corrections for annual variation. 

 They are small, in no instance amounting to 0'.6. Assuming these 

 corrections, as well as those for secular change, to be applicable to 

 the years 1853, 54, and 55, with sufficient accuracy for the purpose in 

 view, the corrections applied to any one of the monthly means, in 

 order to reduce it to the mean of the year, was found by taking the 

 algebraical sum of the correction for annual variation, and that for 

 secular variation, supposing the latter to be +5.5 X 0'.2606 in 

 January, and to diminish each month by 0'.2606 till it becomes 

 — 5.5 X 0' .2606 in December, 



Inclination. — The annual means of inclination for the years 1841 

 to 1856 are reprinted from p. cxix. of the third Toronto volume. The 

 increase of the inclination from the minimum in 1843-44 was arrested 

 in 1855, from which year the inclination has been steadily diminish- 

 ing. 



Horizontal Force. — From 1845 to 1852, the annual means of 

 the absolute horizontal force are reprinted from p. cxvii. of the third 

 Toronto volume. The number given as the annual mean for 1855, is 

 an imperfect approximation, being the average of the determinations 

 in the four months, September to December. The progressive dimi- 

 nution in the horizontal force so apparent in the annual means prior 

 to 1859 — the year of maximum dip, has been converted since 1860 

 into an increase. 



Total Force. — The annual means of the total force for the years 

 1845-52, as well as for 1855, are derived from the annual means of 

 inclination and of horizontal force by the formula 58)= X sec. 6. For 

 the years 1856 to 1864, the annual means are averages of the monthly 

 values of the total force given in Table IV. 



