126 S.A. CLIMATR AND AVIATION. 



seen a surface wind from the N. at a height of about 2,000 to 

 3,000 feet; this was replaced by a current from the S., whilst 

 higher up still (5.000 to 10,000 feet) the current was from the 

 W. These movements were indicated by the motions of the 

 different layers of clouds. Where these various strata mix, there 

 would probably be turbulent motion, which would be immedi- 

 ately fatal to aviation. A very slight knowledge of the clouds will 

 be sufficient to warn the aviator when these conditions are pre- 

 sent. During summer-time, over the greater part of South 

 Africa thunderstorms are to be ex]:)ected, and these sometimes 

 spring up very suddenly ; in some cases these storms are associ- 

 ated with the line-squalls : in any case, the atmosphere is in a 

 disturbed condition, and full of what the aviators have already 

 pithily named as " holes." All these condition are practically 

 inimical to successful aviation. If, however, these turbulent con- 

 ditions arc absent, the winds at an altitude of anything over 

 100 feet are undoubtedly regular and constant over a very large 

 area, and if taken advantage of, might be rendered of great use 

 in long-distance aviation. Over Rhodesia, the general surface 

 wind is E.-S.-E. ; over the Transvaal N.-E. ; over the Orange 

 Free State N., and over the Western Province of the Cape S. 

 These statements are too general to claim exactitude, and are 

 merely given as a first approximation, and as a peg on wdiich to 

 hang an example; thus if an aviator wished to travel from, say, 

 Pretoria to Capetown and back, taking advantage of the winds, 

 he w^ould pursue an easterly path going and a westerly one re- 

 turning, something like this : IVetoria, Johannesburg, Bloemfon- 

 tein, Port Elizabeth, Capetown, returning by Port Nolloth, thence 

 across the Kalahari Desert to ^lafeking, and then to Pretoria. 

 On two days out of three the winds would be favourable, 

 although now and then a consecutive five to seven days of adverse 

 winds would be met. 



Meteorologists generally record only surface winds, and much 

 work must be initiated and carried out before reliable wind 

 itineraries for aviators can be issued, but the writer feels sure 

 that the conditions in South Africa are peculiarly favourable for 

 such. It is more difficult to state the precision with which the 

 force and direction of the winds could be prognosticated, so that 

 if commercial aviation became possible, predictions could be 

 issued; but there is no doubt that the indications 01 the baro- 

 meter will furnish generalities which the experienced aviator 

 could use with good effect. Even at present it is possible to fore- 

 tell when the conditions indicate the establishment of an anti- 

 cyclonic system (region of high barometric pressure) over South 

 Africa, with its accompaniment of gentle winds ; the breaking up 

 of an anticyclone sometimes takes place very rapidly, for reasons 

 which are at present obscure. During the opposite conditions of 

 affairs (low pressure over the interior of South Africa) fore- 

 casting becomes much more difficult, and one must often be con- 

 tent with the general warning that the atmosphere is ripe for the 

 establishment of disturbed conditions, which may develop into 



