TiiK fLir^rATi': ok louri^nqo marques. 315 



figure is still C(jni])risc(l in the designation of "" moderate rain- 

 fall," but a]:)proaching very closely to that called " light rainfall." 



Lourenco Alarcjues being situated within the dry zone (20° 

 to 30° latitude), so classified according to the laws of circulation 

 of the atmosphere, which are deduced on the assumption of the 

 earth's surface being homogeneous, and furthermore owing to the 

 fact that in these latitudes the rain is scarce when a comi)onent 

 of the wind is diverted from the pole to the ecjuator, will account 

 for the total rainfall being inferior to the average amount of 

 water falling in the tropical zone. 



The examination of a chart of distriljution of rainfall will 

 show that the dry zone is mostly accentuated in the southern 

 hemisphere, on the west coasts of continents, this being due to 

 various causes, such as : prevailing direction of the wind, exis- 

 tence of mountain ranges, cyclonic conditions, etc. The conditions 

 of Lourenco Alarques coincide with this, when neither the heaviest 

 short downfalls, nor moderate rainfalls lasting continually for 

 many hours, are frequent, as often happens in temperate zones 

 and in some parts of the tropical zone. 



[n the Table No. XTI the average monthly and annual 

 amounts of rainfall collected are showm. also the average number 

 of rain}- da}-s according to the records of 14 years. At the 

 Observatory, all days on which an amount of o\er n.T'"'" is re- 

 corded, are considered as rain\' da\'s. 



The months of most rainfall are Decem])er and lanuarv, and 

 the driest are June, July, and August. 



The chart showing the percentage of rain corresponding to 

 the different directions of the wind gives evidence of its abun- 

 dance wdien the latter blows from SSE to SW, but chiefly from 

 the S and then from the SSW. In relation to the other wind 

 directions the percentage is much lower, especially the directions 

 N and NXW. where it is insignihcant. 



A higher percentage of rainfall corresponds to the direction 

 \V, which is due to thunderstorms being more frequent from 

 that side, although showers from various directions are recorded 

 in the most violent thunderstorms. 



Nearly all the al)Ove-mentioned authorities reject not only the 

 theor}' of the prevailing Sl'^ winds, but further that those winds 

 cause the rain in South Africa.- \\v. C. Stewart adds that rain 

 may be expected at Port Elizabeth and East London whenever 

 the winter northwesterly winds veer from north to south in the 

 Cape Peninsula, indicating the ])assage of a disturbance to the 

 north-east, and records the fact that in Port Elizabeth in the 

 only month when the SE was at all prevalent the rainfall was 

 &6 % below normal. 



In Lourenco Marques the most abundant rainfalls corres- 

 pond likewise to the passing of depressions, also sometimes to 

 the veering of the wind from N to S, but more generally on the 

 next day or the following one. It is also worth noting that the 

 months showing greater percentage of wind from SE do not 



