<;KAPHS ON QUIET" DAYS DURING THE TWELVE YEARS i9i TO 1902. 397 



The amplitude of the 6-hour term at midsummer being of the order O^l in D and ly 

 in H, I was originally disposed to regard irregularities such as the above at Kew as 

 mainly, if not entirely, accidental. It is now clear that whilst the irregularities may 

 be accidental in the sense that they arise from special features in the days selected 

 by the Astronomer Royal, they cannot be wholly, or even mainly, assigned to errors 

 of measurement, or purely local causes. 



A reference to Table XX. of (A) shows that the amplitudes of the several terms 

 in D are closely alike at Kew and Falmouth. In the case of H a reference to 

 Table XXII. of (A) shows that the amplitudes of the 24-hour and 12- hour terms are 

 decidedly larger at Falmouth than at Kew ; but the 8-hour and 6-hour terms have 

 similar amplitudes at the two stations. 



13. Table XIII. expresses the monthly values of the c coefficients in D and H as 

 percentages of their arithmetic means, and the three seasonal values as percentages 



TABLE XIII. Variation of Fourier Coefficients throughout the Year (1891 to 1902). 



of their means. The small figures give the excess of the Falmouth percentages over 

 the corresponding Kew ones ((A), Table XXIV.). 



Except in the case of c 4 , where there are apparent discontinuities, the irregularities 

 in the difference between the Falmouth and Kew percentages are surprisingly small. 



