SOUTH AFRICAN CLIMATIC CONDITIONS IN 

 RELATION TO AVIATION. 



By Robert T. A. L\nes, F.R.A.S., F.R.S.E. 



The ideal climate for flying-machines is one of high barome- 

 tric pressure and windlessness, or steadiness of wind. It must 

 be confessed that in these two rec[uirements the climate of the 

 South African Plateau is not ideal. Over the greater part of 

 inhal)ited lands the barometer stands at 30 inches, whereas over 

 the Transvaal it is but 25 inches. Winds, although generally 

 moderate in force, are a marked feature of the climate of South 

 Africa; calms are rare, and sudden wind-storms are not u:icom- 

 mon. These features will be enlarged on. 



Without an atmosphere, neither an aeroplane flying-machine 

 nor a balloon could rise from the ground, but the denser or 

 heavier the atmosphere is, the more easily will these machines rise 

 and remain suspended. If we imagine the atmosphere to become as 

 dense as water, flying-machines would tend to float on its surface 

 like a cork on water. The atmosphere is not nearly dense enough 

 to float an aeroplane, but it will float a balloon which has a reser- 

 voir filled with a gas which is lighter than the air. An aeroplane 

 rises because it is propelled through the air ; the propelling-power 

 is derived from fans driven by an engine. The motion of the 

 fans displaces the air and the machine moves forward, the in- 

 clination of the planes of the machine causing it to ascend or 

 descend. 



These simple principles, which are known to every aviator, 

 show us at once that the lower density of the air over the South 

 African Plateau is unfavourable in itself. It is true that, on 

 account of the decreased density of the air, the engine will 

 revolve more freely, which to a great extent compensates for the 

 decreased density, but friction efl:'ects in the engine are increased, 

 and taken altogether, Jhere is a loss. As aeroplames in Europe 

 have not infrequently ascended to altitudes mucdT_ greater than 

 that of the South African Plateau, we learn that the decrease of 

 density is fortunately not sufiicient to interfere materially with 

 the success of aviation. 



The matter of the winds is umloubtedly the most important 

 in either ballooning or aviation. In the highest regions of the 

 atmosphere, say from 20,000 to 30,000 feet, the movement of the 

 air has always a westerly component— that is, the air moves from 

 N.-W..W. or S.-W. to S.-E., E. or N.-E. This wind is too high 

 to have any influence on aviation, but it is important to remember 

 tliat whatever be the surface wind, the wind will veer, as the 

 altitude above the surface is increased towards the west. This 

 is the normal state of afl:'airs, but in disturbed conditions of the 

 atmosphere, especiallv during the summer season on the High 

 Veld, many cross-currents of air may exist ; thus the writer has 



