(1RAPHS OK "QUIET" DAYS DURING THE TWKLVE YEARS 1891 TO 1902. 405 



winter minimum occurs earlier and is more strongly marked in " magnetics" than in 

 either meteorological element. 



The resemblance lietween the annual variations in the amplitude c, of the 24-hour 

 term in temperature and magnetics was somewhat striking at Kew ((A), 68). This 

 resemblance is also visible in Table XXL, but is decidedly less close. In the case of 

 c, the annual variations in temperature and magnetics are less conspicuously unlike 

 than at Kew, but still wide apart. 



Vapour-pressure and temperature range agree with the several magnetic quantities 

 in showing at Falmouth higher percentages in winter and lower percentages in 

 summer than at Kew. The Falmouth amplitude PI in temperature shows relative to 

 the Kew c, increased percentages at midwinter, but it differs entirely from the 

 magnetic c, in showing still more enhanced percentages at midsummer and largely 

 diminished percentages at the equinoxes. 



The mode of difference between the Kew and Falmouth annual variations in c, is 

 diametrically opposite for temperature and magnetics. 



20. As the existence or non-existence of parallelism between the modes of daily 

 variation of temperature and terrestrial magnetism is of importance in inquiries as to 

 how the diurnal magnetic inequality comes into existence, attention may usefully l>e 

 willed to some further points. 



As remarked in 7 and 8, the mean diurnal ranges of declination at Kew and 

 Falmouth are almost exactly equal, whilst the diurnal range in H is somewhat 

 greatest at Falmouth. The mean difference, however, between the daily maximum 

 and minimum of temperature from 1891 to 1902 was only 9'l at Falmouth as 

 against iy'6 at Kew; whilst taking the mean diurnal inequality for the year from 

 the Meteorological Office's ' Hourly Readings . . ." during the sun-spot maximum 

 period 1892 to 1895, the range was 57 at Falmouth, 10'0 at Kew. 



Again, the amplitudes of the principal Fourier terms in the mean magnetic diurnal 

 inequality at Falmouth are very similar to those at Kew in D and larger on the 

 whole in H. In the case of temperature, however, General STRACHEY obtained the 

 following values for the amplitudes of the three principal terms during a common 

 period 1871 to 1882: 



Further, in 14 we saw that the local times of occurrence of the maxima in the 

 Fourier terms in the diurnal inequalities for D and H were as nearly as possible 

 identical at Kew and Falmouth. General STRACHEY,* on the other hand, al.su 



* ' Phil. Trans.,' loe. at., p. 645. 



