SOfi 



1,1;. s. CHAI'MAX ON THE DIURNAL VARIATIONS OF THE 



second; for X we take the mean value of cos S in our equations, and neglect the 

 seasonal changes ; for Y and Z the terms in cos 6 and sin S are taken separately. 

 The values of the amplitudes of the second component in the several cases are 

 also given. It should be remarked that our calculations have not been carried 

 sufficiently far to give the seasonal variation of the fourth component, but it is less 

 important than the term in cos 6, for such stations as Bombay. We thus obtain the 

 following table : 



From SCHUSTER'S calculations, taking pjpo = 1+cos w, the following table of values 

 of C/C,, in which the seasonal changes are disregarded, is obtained : 



Our observational data only allow us to make the roughest possible comparison 

 with these calculations, and the following table is enough to give an idea of what 

 agreement is present. It is got by taking the mean amplitudes at Bombay, Batavia, 

 and Trevandrum (as many as afford data in each case) for the whole year, combining 

 the columns April to September and October to March together by simply averaging 

 the amplitudes regardless of phase. 



The size of the fourth harmonic shows that the term cos 3 a> in p/p^ has distinct 

 importance, for without the presence of such a term, as the second of the above 

 tables show, there should be no appreciable fourth harmonic at all. As regards the 

 other harmonics, there is little to chose between the two expressions for p/p , though 





