238 



Results of Monthly Observations of [Jan. 27, 



Correcting in a similar manner the horizontal force for the same 

 period, we get : — 



Horiz. Force. Dip. 



From the April to September observations \ o.o^qec n% cq.oq 



(reduced to epoch July 1, 1872) J 



And from the October to March observations } CPft r A G ^ c / ao 



\ 3-869o0 67 54-68 

 (reduced to the same epoch) J 



"We have then for the total force derived from the first series 

 3-86965 sec 67° 53'-89 = 10-28463 British units, and for the second 

 series 3-86950 sec 67° 54'-68 = 10-29013, showing thus a difference of 

 0*00550 as the measure of the greater intensity of the terrestrial magnetic 

 force in the October and March period than in the April to September 

 period. 



The amount determined from the first six years' observations by 

 Sir E. Sabine was 0-00317 ; the second six years, 1863 to 1869, gave 

 0-00363. 



Absolute Declination. 



The observations of declination made with the Kew Unifilar during the 

 periods corresponding to those for which the force and dip observations 

 were discussed have not been published, a much more elaborate series 

 of observations being available in the records of the Kew self-recording 

 Declinometer. 



These were fully treated by Sir E. Sabine for the years 1857 to 1862 

 inclusive, in the Philosophical Transactions for 1863, page 290 ; and a 

 paper carrying the investigation up to the end of 1873 is now in course 

 of preparation. 



"We here give the results of the observations made monthly, in a form 

 similar to that in which the force and dip observations are drawn up. 



Table VI. 



The Monthly observations of Absolute Declination at noon, observed 

 with the Declinometer. 



Month. 



1869. 



1870. 



1871. 



1872. 



1873. 



1874. 



Mean of 

 six years. 



April 



May 



June 



July 



August . . . 

 September 



20 31 233 

 20 33 35-8 

 20 33 392 

 20 34 39-8 

 20 30 44-5 

 20 24 51-8 



20 25*49-2 

 20 32" 17-2 

 20 25 5-5 

 20 25 45-7 

 20 23 18-4 

 20 24 24-2 



20 17 59-0 

 20 16 433 

 [20 16 48-8] 

 20 16 54-4 

 20 20 5-8 

 20 15 59-0 



20 8 49-4 

 20 3 219 

 20 10 43-6 

 20 10 11-7 

 20 6 54-3 

 20 7 20-4 



20 2 8-0 

 19 53 19-1 



19 56 45-3 



20 1 43-4 

 19 55 5-7 

 19 59 49-2 



o / /; 



19 51 211 

 19 53 38-8 

 19 49 44-4 

 19 49 35-0 

 19 49 235 

 [19 49 29-8] 



20 12 55-00 

 20 12 9.35 

 20 12 7-80 

 20 13 8-33 

 20 10 5503 

 20 10 1902 





20 31 29-07 



20 26 672 



20 17 24-72 



20 7 53-55 



19 58 8-45 



19 50 32-05 



20 11 5576 



