[jackson] 



MAGNETIC DECLINATION AT AGINCOURT 



111 



of the maximum spot period is to bring the winter and summer values 

 nearer together. The seasonal diurnal inequalities during maximum 

 and minimum spot periods are exhibited graphically in Plate III. 



The diurnal inequalities for these groups of years were also treated 

 by the method of Fourier analysis and the resulting Fourier coefficients 

 are given in Table V. 



Table V. 



Fourier Coefficients. Declination at Agincourt. All Days using 

 75th M.T. 1902-1912. 



Comparing the amplitudes of the different terms we see that 

 during the maximum spot years the seasonal variation is reduced in 

 each term, and that the amplitude is greater in the 24 hour term 

 and the 12 hour term but on the average it is smaller in the 8 hour 

 term and practically the same in the 6 hour term. A comparison 

 of the phase angles shows that the occurrence of maximum in any 

 term is earlier in years of minimum spots, but varies with the season 

 and to a different amount in the different terms. In the twenty-four 

 hour term the average time for the year is 24 minutes and varies from 

 12 at the Equinox to 72 in the winter. In the 12 hour term the average 

 is 26 minutes earlier and varies from 14 in the summer to 56 in the 

 winter. In the 8 hour term the average is 19 minutes earlier and 

 varies from 11 in summer to 47 in winter and in the 6 hour term the 

 average is 1 1 minutes and varies from 6 in summer to 15 at the Equinox 

 These results are tabulated below in Table VI. 



