ox “QUIET” DAIS DURIXG THE ELEVEN YEARS 1890 TO 1900, ETC. 431 
analysed into Fourier terms is no proof of the existence of “distinct physical 
influences operating in recurring cycles of 24, 12 . . . (hours).” He has in fact 
shown tliat the simple hypothesis that the heating effect of the sun varies as- the 
sine of his altitude, being nil when the sun is below the horizon, gives rise to 
Fourier series which constitute not at all a bad first approximation to the results 
actually found at certain stations. 
Accepting this contention, we may however get much useful information from the 
Fourier’s analysis. For instance, we know that the consequences of surface heating 
on underground temperature can be most easily arrived at by an analysis which 
treats the Fourier terms as independent entities. Also the examination of differences 
lietween the relative values of c coefficients at different seasons of the year, or in 
different years at the same season, is perhaps the most hopeful way of ascertaining 
community of origin in different phenomena. 
§ 68. Keturning to Table XLVIII. we see that in the case of there is a very 
close resemblance between the annual variations in temperature and magnetics. The 
agreement is just about as good as that Ijetweeu the temperature results for Kew and 
Greenwich, and decidedly lietter than tliat between some of the individual magnetic 
elements at Kew. Tlie difference between December and January is certainly less 
conspicuous in temperature than in magnetics, Imt still at both Kew and Greenwich 
the December temperature mean is the lower. 
In the case of and Cg the temperature results at the different stations differ more 
widely than in the case of Cj, but clearly the law of annual variation is here altogetlier 
different from that appearing in magnetics. The temperature data for seemed too 
small and uncertain to be worth detailed consideration. 
As regards the relative importance of the different Fourier terms in temperature 
and magnetics, the following are the ratios for the yearly means ;— 
g/a- 
(■si Cl. 
g/a- 
Temperature (after Strachey) mean from Greenwich . 
■ill 
•08 
•03 
II >) ,, 7 British stations . 
•23 
•10 
•32 
hlagnetics (at Kew) mean from D, I, H and V. 
•64 
■13 
This shows the much greater relative importance of the 24-hour term in temperature 
than in magnetics. The difference is probably even greater than tlie figures suggest. 
The magnetic values of Cj, &c., refer to mean inecpialities for tlie year; whereas 
General Strachey’s corresponding values represent arithmetic means of 12 monthly 
values, and his phase angles are most variable in the shorter period terms. It v/ill be 
seen in fact that the values obtained tor m/cq, &c., from the mean temperature 
inequalities for 1892 to 1895, or 1889, 1890 and 1899, in § 62, are less than the 
values we have-just derived from General Straohey’s fio-nres 
