22 



Dr. C. Chree. An Analysis of the Results from [May 1, 



"An Analysis of the Results from the Kew Magnetographs on 

 Quiet Days during the Eleven Years 1890-1900 W1 th a 

 Discussion of certain Phenomena in the Absolute ^Observa- 

 tions." By CHAELES CHREE, Sc.D, LL.D, F.R.S Super- 

 intendent of the Observatory Department. Received May 1, 

 Read May 28, 1903. 



(From the .National Physical Laboratory.) 



(Abstract.) 



The late Kew Observatory Committee joined in 1890 in a scheme, 

 whereby five days each month were to be selected as magnetically 

 quiet days by the Astronomer Royal, with a view to the curves on 

 these days being tabulated by observatories which did not care 1 

 undertake the tabulation of every day's curves. That scheme has 

 been persisted in, and the present paper deals with the results it 

 has led to during the eleven years 18901900. The paper treats of 

 the secular change in the several elements, of the annual inequality, 

 of the diurnal inequality, and the non-cyclic effect in the diurnal 

 variation. Attention is more particularly given to the declination, 

 inclination, and the horizontal and vertical components, but some 

 consideration is also given to the northerly and westerly components 

 of the horizontal force and to the total force. 



Diurnal inequalities are got out for each month of the year in the 

 principal elements. These inequalities are analysed into Fourier's 

 series, and the variation of the Fourier coefficients is traced throughout 

 the year. Attention is also given to the variation throughout the 

 year in the ranges of the diurnal inequalities and in the sum of the 

 twenty-four hourly differences from the mean for the day. The 

 diurnal inequalities are shown graphically in various ways, serving 

 to illustrate different features. 



As explained in a " Preliminary Note," the relations between 

 magnetic phenomena and sun-spot frequencies have been investigated. 

 The present paper treats of this investigation in detail. Attention 

 is given to the ranges, and the sum of the twenty-four hourly 

 differences from the mean of the day in the diurnal inequalities, 

 and to the amplitudes and phase angles of the terms in the Fourier 

 series representing these inequalities. Some of the results obtained 

 for Kew are compared with corresponding results for Wilhelmshaven 

 and Pare St. Maur, based on data given by Borgen and Moureaux. 

 The results from the stations compared showed a very good 

 agreement. 



It is found that the non-cyclic effect in the diurnal variation, 

 and the variability in the declination recently discussed by the 



