Diurnal Meteorological Conditions at Kiniberley. 151 



u^ has the usual winter maximum, and also the common equinoctial 

 minima. In the Northern Hemisphere, however, the smaller minimum 

 is in September, and the larger in March. In the Southern Hemi- 

 sphere the smaller minimum is possibly pretty generally in October, 

 and the larger in March. At Kimberley the two are nearly equal. 

 At Melbourne, according to Cole's Tables, the October minimum 

 almost vanishes ; while at Cordoba, on the other hand, the March 

 minimum is relatively very small. 



The angle Y^ backs during upwards of half the year from near 

 360° in February, to near 180° in August ; a sudden change then 

 returning it to 360°, whence it veers rather more than half a right 

 angle. There seems to be a tendency to a maximum in the ampli- 

 tude W4 just before these sudden changes, and a minimum afterwards. 

 The quantities in question are, however, so very small that no great 

 weight should be attached to the results in their case from so small 

 a period of observation as four years. 



Table 29 gives annual values of the harmonic constants deduced 

 after varying certain of the presumably influential factors. The first 

 column of constants is computed from Table 27, the second from 

 Table 26, the third, fourth, and fifth from Tables 17, 20, and 15. 

 In these last three no allowance or correction has been made for the 

 secular variation ; but in the first two, because of the noteworthy 

 constancy of the ranges B, C, and D, above, this correction has 

 been made. This of course introduces some discordance into the 

 comparison. 



If we consider first the differences between clear and cloudy days 

 we see a large difference in the phase-times of the first components. 

 As in the case of the temperature, that of the cloudy days is the 

 earlier, and by fully three times the amount. Nevertheless, while 

 a cloudy day accelerates the phase-time of temperature by half as 

 much again as a clear day retards it, in the case of the pressures the 

 time-ratio is almost exactly the other way about. The phase-times 

 of the second component are practically identical, as are also the 

 nearly equal amplitudes u^ and u^. So far this is in accordance with 

 Hann's rule, i.e., (1) "I have shown that the remarkable difference 

 in the daily march of the barometer with difference in weather is 

 entirely due to a modification of the diurnal pressure curve, and that 

 the corresponding differences in this wave have the same character 

 as the differences between the diurnal curves on land and at sea, 

 and that both are probably due to the same causes." (2) "The 

 double daily oscillation ... is subject to quite simple laws, and is 

 not affected in either amplitude or phase-time by the weather." 

 On the other hand, the third component is an exception. Of this 



