Variation of Temperature in the British Ides, &c. 77 



not only in the twenty-five years, the nine years, the five years, and 

 the four years, but also, and to an exaggerated extent, in the 

 typical single year. The higher-order effects vary very much both in 

 magnitude and in position, but the second-order effect is prominent 

 in all the curves, and, except in the very exceptional years whose 

 abnormality t it shares, it has its maxima oscillating over the first ten 

 days of February and August respectively. This oscillation again 

 shows itself in the gradual decrease of the amplitude of the second- 

 order effect as the number of years increases whose mean curve is 

 analysed. Thus for the single year the amplitude is 3'57 F. ; for the 

 five years it is 2 -06 F. ; for the nine years 1'95 F. ; and for the 

 twenty-five years, 1'38 F. Thus Table I is in itself a sufficiently 

 striking demonstration of the existence of a second-order meteoro- 

 logical effect which combines with the primary solar effect to give us 

 our normal periodic variation of atmospheric temperature. 



The gradual diminution of the amplitude of the second-order 

 oscillation with the extension of the time over which the means are 

 calculated, might perhaps be taken to indicate that if the means were 

 sufficiently extended it would disappear altogether ; and the fact that in 

 hundred-year means for Vienna (which will be referred to later), the 

 second-order amplitude is reduced to one degree, whereas the first-order 

 amplitude is 19'8 F., might be regarded as a further indication of the 

 same fact. In the absence of data extending over the whole period it 

 is, of course, impossible to form a definite opinion, but if the arrange- 

 ment were so that the effect which appears in twenty-five-year means 

 is obliterated in a hundred years, it would be very interesting to know 

 how the second -order effect appeared in the other three groups of 

 twenty-five years of which the hundred are made up. Some light 

 might be thrown upon the matter by the analysis of all the com- 

 ponent years of the original twenty-five, but this has not yet been 

 carried out. 



The fact that the maximum of the second order for Vienna comes 

 on March 24 shows that the remaining effect there is different in 

 character from that shown in the curves for the British stations. 



Comparison of the Effect at Kew with that at the otlier Stations. 



Reference has hitherto only been made to the Kew curves, since it is 

 the Kew temperatures which have been studied in detail, but the 

 analysis of the twenty-five-year mean temperature curves for Aberdeen, 

 Valencia, and Falmouth are also given in Table I. The second-order 

 curve is in each case about one-eighth of the first-order curve in ampli- 

 tude, but the third-order curve is not always entirely negligible. At 

 Kew its amplitude is only one-thirtieth of the second-order curve 

 amplitude, and at Falmouth it is only one-seventh, so that in these 



