1887.] Storms of South Africa. 239 



north-east. A portion of the south-east trade flowing from the 

 high pressure area over the South Indian Ocean is deflected and 

 drawn towards this area of low pressure, and intensifies the north 

 wind which flows on to the Colony. How far the geographical 

 distribution of mountains and plains affect this deflection is an open 

 question, but I have no doubt as important a part is played by these 

 in South Africa as in other places. 



When any great disturbance takes place at the equator, a strong 

 current sets in off the tropical bank, towards the point of disturbance, 

 and the portion which mingles with the northerly current before- 

 mentioned, increases its intensity considerably, and forces it further 

 on to the Colony. Here it meets the south-east current of the tradesy 

 and a semi-cyclonic movement is generated, but as the pres.sure of 

 the advancing and opposing currents is greater than the lateral 

 pressure, the area of disturbance formed will be of an oval shape^ 

 an ellipse in fact, the minor axis being along the point of greatest 

 pressure. Various modifications of this form are experienced when 

 the advancing and opposing currents do not meet at an angle of 

 180° but at a smaller one. 



The north wind, having passed over a tropical portion of the earth, 

 is, as a rule, warmer than the south-east one, consequently it flows 

 up and over the latter, while the south-east wind is deflected and 

 flows more easterly, until reaching the edge of the high pressure 

 area to the south-west of us, the combined forces of the winds 

 increase their power to a very great extent. 



So that when an area of low pressure extends across the Colony 

 the winds will flow direct in to it from the north-east, north and 

 north-west, but will flow round it on the south and west sides, as 

 east and south-east winds. 



As the power of the north current increases, it forces its way on to 

 the Colony, the area of low pressure thus advancing, until the 

 constant overflow above on to the area supplying the south wind, 

 and its consequent banking up, causes a return oscillation. At the 

 time when the two currents are stationary (which sometimes lasts 

 for days, when the currents are balanced in intensity) the winds 

 blow strongest, and often independent cyclones form in the low 

 pressure area between them and roll off to the east. This I have 

 noticed over and over again. When the south current has gained 

 the victory, it gradually pushes the north one back again, but as 

 this south current generally comes from the south-west, in the form 



