DAILY VARIATION. 



183 



It was also found from observations made in the northern hemisphere that 



b =0-937 cos^.^ 



B=154:° 



c =-137 (sin2 -1) 

 C =105" 

 Thus the amphtude and phase at any place can be obtained at once from the relationship 



02 sin (2a; -I- Aa) =0-937 cos^ </> sin (2x + 154°)+0-137 (sin2 <p -i) sin (2a; + 105°— 2X) 

 ill which (ft and X are the latitude and longitude of the place. 



The necessary calculations have been made for the Antarctic stations and are included 

 in table 103. 



■ Table 103. 

 Twelve-hourly barometer oficiUafion. 



In column 4 the calculated values of b, i.e., the amplitude of the wave travelling round 

 the earth, are given, and in column 5 the calculated values of the amplitud'i of the oscilla- 

 tion outwards from the Pole. In column 6 are given the values of A2 as calculated for each 

 station, while in column 7 are given the observed values. Columns 8 and 9 contain the 

 difference between the observed and calculated values of Ao in angles and time respectively. 

 From column 9 we see that at five of the six stations the observed time is within half an 

 hour of the calculated time. 



The calculated and observed values of r?.2 in columns 10 and 11 do not agree quite so well. 

 The ratio of the calculated to the observed values of ao are given in column 12, from which 

 it will be seen that all the calculated values are too large. It is, however, significant that 

 the two stations which have the best agreement between the calculated and observed values 

 of A2, South Georgia and Gauss Station, have also the best agreement between the calculated 

 and observed values of 02, and roughly speaking the agreement of 02 at the other stations 

 . is in the same order as the agreement of A2. 



Considering the smallness of the amplitudes — all but one less than one-tenth of a 

 millimetre — and the fact that they are obtained in a region where the non-periodic barometer 

 changes are so large, it is amazing that such short periods of observations give values which 



