[ 373 ] 



X. An AiinJifxiis of the AV.V////.V /;/ tin- r<ilni'Hillt .\/<i</ii<t(> ; /rfi/>/t* on " Quirt" 

 Days (lnriii,j t/ir Tweln- )w/-.s 1H<)1 to 1902. 



By CHARLES CHREE, Sc.D., LL.D., F.lt.S. 

 (Fnn the National Physical 



Received November 23, Read December 15, 1904. 



CONTENTS. 



Sections Pago 



1. Introduction 373 



2. Secular change 375 



3-5. Non-cyclic effect 376 



G-10. Solar diurnal inequality * . 384 



11. Vector diagrams 387 



12-14. Analysis of the diurnal inequality in Fourier series 393 



15-16. Variation throughout the year (Fourier series) 400 



17-20. Relations with meteorological phenomena 402 



1. IN May, 1903, I communicated to the Society a discussion of the results obtained 

 from the Kew magnetographs during the eleven years 1890 to 1900, on the five 

 quiet days a month selected by the Astronomer Royal. That paper will for shortness 

 be referred to as (A). 



When dealing with data from a single station, even when representing many 

 years' observations, one is confronted by the possibility that the results may be 

 appreciably modified by defects peculiar to the apparatus or to the methods of 

 observation employed, or that they may be largely dependent on local conditions, and 

 so of very limited applicability. For these reasons alone, it was desirable to discuss 

 on parallel lines data from a second English observatory. Another reason for such 

 an investigation was the disturbed magnetic conditions introduced at Kew in 1901 

 by electric trams. In consequence of their action, there is unlikely to be any 

 adequate opportunity for comparing simultaneous undisturbed data from Kew and 

 the new magnetic observatory now under construction in Eskdalemuir. Thus the 

 most promising way of securing continuity is a minute comparison of Kew with some 

 observatory IH>\\ existent whieli is likelv t<> <-,>nt inue t'n-f tn.m Ij.un di>t ui i.ani-rs I'm 

 some time. Both sets of considerations pointed to a discussion of the results obtained 

 at Falmouth Observatory. Magnetographs have been in constant operation at 



(381.) 4.5.05 



