Falmouth Magnetograms on " Quiet" Days, 1891 to 1902. 323 



"An Analysis of the Eesults from the Falmouth Magnetograms 

 on ' Quiet ' Days during the Twelve Years 1891 to 1902." 

 By CHARLES CHREE, Sc.D., LL.D., F.K.S., Superintendent of 

 the Observatory Department of the National Physical 

 Laboratory. Eeceived November 23, Eead December 15, 

 1904. 



(From the National Physical Laboratory.) 

 (Abstract.) 



The paper contains an analysis and discussion of the results obtained 

 from the declination and horizontal force magnetograms at Falmouth 

 on quiet days from 1891, when the records commenced, until 1902. 

 The discussion proceeds on parallel lines to those followed in dealing 

 with the corresponding Kew* data for 1890 to 1900, and a comparison 

 is instituted in many cases between Kew and Falmouth results. 



The total secular changes of declination from 1891 to 1900 at Kew 

 and Falmouth were identical, and the changes from year to year were 

 closely alike. In horizontal force the annual changes recorded at the 

 two stations did not agree so closely, and on the average the change at 

 Falmouth was somewhat the greater. 



When discussing the " non-cyclic effect " in the diurnal variation of 

 the declination at Kew, it was pointed out that though so small and 

 irregular as to be possibly attributable to accident, it yet presented 

 features suggestive of a true physical origin. Though differences exist 

 between the phenomena at Kew and Falmouth, still the points of 

 agreement are such as to give strong support to the view that the 

 phenomenon is not accidental. 



The data considered being the means from the five selected quiet 

 days a month, out of the 120 months in the 10 years 1891 to 1900 

 common to the two investigations, there is agreement of sign in the 

 non-cyclic effects at Kew and Falmouth in 69 cases and disagreement 

 in only 22, the effect being nil at one or both stations in the remaining 

 29 cases. Also at both places the sign of the non-cyclic effect, though 

 prevailingly positive throughout the year, is distinctly negative near 

 midsummer, and the seasonal variations in the two cases are fairly 

 alike. 



In horizontal force the non-cyclic effects at Kew and Falmouth are 

 large and closely alike. From 1891 to 1900 there were only 5 months 

 in which the non-cyclic effects differed in sign, as against 99 in which 

 they agreed, and the mean values of the effects at the two stations 

 differed by only about 5 per cent, of the mean value at Kew. 



Whilst the mean daily range of temperature at Falmouth a seaside 

 station- is notably less than at Kew, the daily ranges of declination at 



* ' Phil. Trans.,' A, vol. 202, p. 335. 



