The Climate of East London, Cape Colony. 225 



at Durban, East London, and Kimberley, while a hot wind is blow- 

 ing at either of the former places, and the fact that the direction is 

 always off-shore, there surely can be no reasonable doubt remaining 

 that they are true Foehn winds, strongly resembling those of the 

 lower slopes of the Alps described by Hann.* Nevertheless this is 

 not to say that a South African hot wind is wholly explained. There 

 seems to be a probability that some subsidiary process is involved 

 in generating these high temperatures in addition to the adiabatic 

 heating of a downcast current of air. We have seen that there are 

 occasional temperatures during April of 90° at 8 a.m. at East 

 London. Now the April mean temperature of the air at Queens- 

 town, 100 miles north-west from East London, at 8 a.m., is 57°'6. 

 If this air could flow at once to East London it would acquire a 

 temperature, due to compression in falling 3,500 feet, of about 18 0, 7 

 more, making it 76°'3. We shall have, therefore, to account in some 

 way for another 14° to get the observed temperatures. But air 

 from inland must necessarily take time to reach the coast, so that 

 Queenstown air would have to start some hours before 8 a.m. to get 

 to East London at that time. If we assume that it starts before 

 sunrise while at its mean minimum temperature of about 49°, it 

 would acquire an additional 18° - 7 in its descent and a small rise on 

 account of diurnal temperature variation. This last would be less 

 than it would have experienced if it had remained at Queenstown, 

 because the coast variation is much less. It seems, then, that we have 

 nearly 20° to account for if we assume the air to start from Queens- 

 town at its normal temperature. Of course the temperature at 

 Queenstown may be higher than usual to begin with, as it is at 

 Kimberley at the same time ; but it is not likely to be 20° above the 

 normal. And if it were we should still have to account for it at 

 Queenstown instead of at East London, and so only have shifted the 

 incidence of our difficulty. At King William's Town, 30 miles from 

 East London and 1,300 feet above the sea, the April mean tempera- 

 ture of the air at 8 a.m. is 63°-6. Adding 7° for adiabatic increase 

 of temperature due to compression, and we have, as before, nearly 

 20° of rise still to explain, assuming the air to start from King 

 William's Town at its normal temperature. Of course, if the rise of 

 temperature is all adiabatic, then we must conclude that the air has 

 started from higher levels, above the surface, say from an altitude of 

 7,000 feet at a temperature of about 53°. But it seems more likely 



* See, inter alia, J. Hann, Met. Zeit., January, 1904, p. 42. C. Stewart, 

 Science in South Africa, p. 40. Also for comparison, Bartholomew's Atlas of 

 Meteorology, p. 33 and Plate 32, 1899. J. Hann, Lehrbuch der Met., p. 595, 

 1901. Handbook of Climatology, ch. xix., 1903. 



