Diurnal Meteorological Conditions at Kimherlcy. 163 



characteristics in the unresolved and unreduced curve of wind 

 velocity. 



Now the curve of wind velocity is to a very large extent a curve of 

 temperature, and so also is the curve of east component direction. 

 But the north component is not. If we consider separately each 

 hourly meridian in the latitude of Kimberley we find that the 

 numerical values of the north component of velocity moving along 

 them are different for each ; and at some small distance, say a few 

 miles, north or south of Kimberley we should still, probably, obtain 

 the same values for the same meridians — or even if the values were 

 different, their ratios, between north and south stations, of the same 

 meridian, could not differ largely. Hence there should be no 

 inherent likelihood of discovering any underlying diurnal tem- 

 perature or pressure affinities in the north component variation, for 

 ' this reason. But the east component, moving very nearly along 

 the Kimberley parallel, reveals quite a different state of things. 

 Its numerical value varies, so that no two adjacent hourly arcs 

 contain the same amount of surface wind-movement. There 

 must, then, be local compression and exhaustion of air, according 

 to circumstances, at the different meridians. Suppose the time 

 to be noon, for example. Along the hour-arc to the east, i.e., 

 from noon to XIII., the annual average value of the east 

 component is minus 1,095, or, otherwise, there are 1,095 miles 

 of wind from the west. xVlong the hour-arc to the west, i.e., from 

 XI. to noon, there are 865 miles from the west. That is to say, 

 230 more miles of wind are moving from the meridian than to it. 

 Therefore there is an exhaust which the north component cannot 

 altogether fill, because much the same exhaust will be found for 

 some distance north and south along the same meridian. Here, then, 

 is a remarkable circumstance : an actual variation in the quantity of 

 air due to the veering of the surface wind current. Does it stand as 

 a link in some probable sequence of cause and effect ? 



The magnitude of the increase, positive or negative, at each 

 meridian will be found in the last column of Table 43. The first 

 fourteen meridians show an outflow, the other ten an influx. The 

 IX. meridiail has the greatest deficit ; that of XVIII. the greatest 

 surplus. The actual minimum is some time after IX. ; the actual 

 maximum some little time before XVIII. Thus they seem to 

 follow, and depend upon, the principal maximum and minimum of 

 the barometer. The first effect of the thermal expansion of the air 

 after sunrise, and of the contraction before sunset, respectively, is 

 an increase and decrease of pressure. The second effect is an air 

 movement, outwards or inwards, to relieve the disturbed tensions. 



