324 Dr. C. Chree. Analysis of Results from Falmouth [Nov. 23, 



the two places are as nearly as possible equal, and the daily range of 

 horizontal force is somewhat larger at Falmouth. 



The annual variation of temperature range is again notably less at 

 Falmouth than at Kew, the winter range at the former station 

 being relatively high, and the summer range low. There is in 

 this case a somewhat analogous state of matters in magnetics, the 

 difference between the diurnal ranges at midsummer and midwinter 

 being relatively less at Falmouth than at Kew, but the phenomenon is 

 less marked than in temperature. 



Analysing the diurnal inequality of temperature into harmonic 

 terms of 24, 12 and 8-hour periods, General Strachey* found that 

 the local time of occurrence of the maxima was distinctly earlier at 

 Kew than at Falmouth, the difference being greatest for the 24-hour 

 term, for which it amounted to nearly an hour. When the declination 

 and horizontal force diurnal inequalities are similarly analysed, the 

 local times of occurrence of the maxima are so nearly alike at the two 

 stations that it is impossible to say with certainty which is the earlier. 

 If a difference exists, it is of the order of only one or two minutes of 

 time. 



This last result applies to the average year of a sun-spot cycle. It 

 has already been found that the time of occurrence of the first maximum 

 in the 24, 12 and 8-hour terms at Kew varies with sun-spot frequency, 

 being later in years when spots are numerous than when they are few. 

 Thus the sun-spot maximum period 1892 to 1895, as compared to the 

 sun-spot minimum period 1890, 1899 and 1900, showed a retardation 

 of 15 J minutes in the time of occurrence of the maximum in the 

 24-hour term. The phenomena at Falmouth are closely similar, the 

 retardation in the 24-hour wave in the period 1892 to 1895, as 

 compared to the sun-spot minimum period 1899 to 1902, amounting to 

 14 minutes. 



When the annual variations in the amplitudes of the daily ranges in 

 declination and horizontal force at Kew, and of the 24, 12 and 8-hour 

 terms in the diurnal inequality, were expressed as Fourier series, with 

 an annual and a semi-annual term, there proved to be a remarkably 

 close agreement between the dates of occurrence of maximum in the 

 annual terms, and also in those of the semi-annual terms for the several 

 elements. The same phenomenon appears at Falmouth, and there 

 proves, moreover, to be a remarkably close agreement between corre- 

 sponding Kew and Falmouth dates. Thus taking for both declination 

 and horizontal force the three most important quantities considered, 

 viz., the amplitudes of the diurnal ranges and of the 24-hour term in 

 the diurnal inequality, and the sum of the 24 hourly differences from 

 the mean for the day, and considering both the annual and semi-annual 

 terms, we have 12 dates for the occurrence of the first maximum at 

 * ' Phil. Trans.' for 1893. 



