DAILY VARIATION. 



179 



Fourier Coefficients. 

 The Fourier coefficients have been obtained as foilowa. The coefficients have been cal- 

 culated from the actual departures from the mean for 



(a) each month and season in 1911 and 1912 separately, using 24-hourly values ; 

 (&) each month and season in 1911 and 1912 combined, using 24-hourly values ; 

 (c) each month and season in 1902 and 1903 combined, using 12-hourly values. 

 In order to combine the two periods 1902-03 and 1911-12, one of which has 24-hourly 

 values and the other only 12, two methods were adopted. First, the actual departures for 

 every two hours were combined from the four years' observations giving twelve values in 

 the day (those plotted in figure 59) which were then analysed in the usual way; and secondly, 

 the coefficients obtained by (&) and (c) were combined algebraically. The latter method is 

 preferable, as it uses all the observations made, while the former discards all alternate hours 

 in the 1911 and 1912 period. As a matter of fact the results of the two methods varied 

 very little, but the double calculation was a useful check. The results for the four years 

 combined, published and discussed here, are those obtained by the second method. 

 The series used is the ordinary one : 



dB = «i sin (Ai-t-x) -f- a2 sin (A2 + ix) -f as sin (As-j-Sa;). 



Table 100. 



Fourier coefficients of the d%ilij v.iriation of the baroinster at McMurdo Souiul based on the 



-periods February 1902 to January 1904 and February 1911 to December 1912. 



