1887.] Storms of South Africa. 243^ 



Bearing this in mind it will be noticed that, as the air at A is 

 carried up to B, and contains moisture in an invisible state, this 

 moisture will condense and form clouds at that level. As fresh moist 

 air rushes up, fresh clouds will be formed, each one being larger and 

 more complete than the last, till at A the type will be the large 

 cumulus and cumulo-stratus. As the cloud forming moisture is 

 carried up by the ascending current, a portion will be conveyed back 

 by the return overflow above and being precipitated through the 

 atmosphere at N form various sorts of elouds there. According to 

 the amount of moisture carried up, so will the clouds at N accumulate, 

 and ultimately rain will fall. The direction of the clouds will be 

 parallel to G.H.K.L. on Fig. 2. Those at G will be faint horizontal 

 streaks of cirro-stratus, sometimes barely visible to the eye. Follow- 

 ing these at H will come nodules of cirro-cumulus. The pinnacles 

 of these nodules penetrating into the great west upper current above 

 the line B.M. (on Fig. 1) will be blown into thin streaks or threads 

 and form the cirro-filum or thread cirrus. Simultaneous with the 

 dispersion of the upper portions of these nodules, a precipitation will 

 take place into the lower current, the rain being blown towards A 

 on Fig. 1. At K and L (Fig. 2) the clouds will be larger and more 

 perfect in form, till at A, the heavy cumulus, cumulo-stratus and 

 nimbus are formed. Beyond A in the equatorial current, hard 

 rounded cumulus, with intermingled stratus merging into cirro-- 

 cumulus and high mottled cirrus will be found. No cirro-stratus 

 will be found on this side of the centre. All along the line A.B. (Fig. 

 1) the clouds form, and are apt to impinge into the upper current. 

 When this is the case, a precipitation is sure to take place, and if 

 the altitude is not too great, will rsach the ground, hence the area 

 of precipitation (shewn by the dotted lines on Fig. 2) is always 

 more on the polar side than on the equatorial one. This is why we 

 have more rain, with our winter storms, after the centre has passed^ 

 than before. 



And now let us study for a few minutes the movements of the 

 barometer during the passing of the system. E (Fig. 1) is a warm 

 current and consequently light, while D is a cold one and of course 

 heavy, but if the whole system is moving towards the south, the 

 intensity of E must be great enough to overcome the weight of D, 

 and consequently the pressure at N must be greater than at D. From 

 C to A the heavier current is gradually becoming less, the current E 

 being much lighter, hence the barometer will gradually fall from. 



