and certain Electrical Phenomena. 487 



Thunderstorms seem to be much more prevalent along the 

 east of Africa than in other parts, and electrical phenomena 

 are most striking in connexion with winds that have traversed 

 arid sandy regions. This is shown in the Kalahari desert. 

 Mr. Wilson remarks* : — " Towards Basutoland, from Novem- 

 ber to April, the N.E. wind blows from the shores of the Mo- 

 zambique and the delta of the Zambesi immense masses of 

 cloud which sweep heavily over the earth, darkening the sky 

 and preceded in their course by dreadful peals of thunder. 

 In the great Naniaqua-land, as well as in the desert, rain falls 

 only from thunder-clouds. These rise from the N.E. There 

 is something terribly sublirue in a real Kalahari thunder-storm. 

 There are the usual premonitory appearances. At length a 

 cloud of dust approaches, a storm of wind rushes over the 

 plains, a few large spattering drops are heard, and then, with 

 an almost simultaneous blinding glare of lightning and deaf- 

 ening crash of thunder, torrents of mingled hail and rain 

 descend. In a few minutes the country is flooded. In an 

 hour the storm has passed. Moffat states that in this district 

 the lightning is of three kinds : one passing from cloud to 

 cloud ; another, forked, passing through the cloud and striking 

 the earth ; the third, and most common, is stream-, or chain- 

 lightning. It appears to rise from the earth in figures of 

 various shapes — crooked, zigzag, and oblique f, and sometimes 

 like a waterspout at sea ; it continues several seconds, while 

 the observer can distinctly see it dissolve in pieces like a 

 broken chain. The perpetual roar of awful thunder on these 

 occasions may be conceived, since some 20 or more flashes 

 may be counted in a minute. The lightning may also be seen 

 passing upwards through the dense mass of vapour, and 

 branching like the limbs of a naked tree on the blue sky 

 above." 



Mann \ says of Natal, that the thunderstorms are of great 

 intensity, but of short duration ; clouds gather over the hill- 

 tops and then spread rapidly out into the valleys. The storm, 

 for the most part, breaks first in the hills and then moves 

 rapidly off towards the east. The lightning is often extremely 

 beautiful, the path of the discharge not unfrequently being 

 seen upon the background of the clouds as a broad quivering 

 ribbon. Paraboloid and elliptical discharges amidst the clouds, 

 with descending or radiating lines setting off from them, are 



* Journal of the Royal Geographical Society, xxxv., 1865. 



t The form is doubtless dependent on the presence of conducting-par- 

 ticles in the air ; but, whatever the form, it can only be momentarily 

 or intermittently visible. 



X Journ. Roy. Geogr. Soc. xxxvii. pp. 66, 67 (1867). 



2 L2 



