EBB AND FLOW IN THE LAKE. 



143 



defined. The periodical winds over the Lake — regular, 

 but not permanent — are the south-east and the south- 

 west, which also bring up the foulest weather. The 

 land and sea breezes are felt almost as distinctly as upon 

 the shores of the Indian Ocean. The breath of the 

 morning, called by the Arabs El Barad, or the zephyr, 

 sets in from the north. During the day are light va- 

 riable breezes, which often subside, when the weather is 

 not stormy, into calms. In the evenings a gentle afflatus 

 comes up from the waters. Throughout the dry season 

 the Lake becomes a wind-trap, and a heavy ground sea 

 rolls towards the shore. In the rains there is less sea, 

 but accidents occur from sudden and violent storms. 

 The mountainous breakers of Arab and African in- 

 formants were not seen ; in fact, with a depth of three 

 feet from ridge to dell, a wave would swamp the largest 

 laden canoe. Wind- currents are common. Within a 

 few hours a stream will be traversed, setting strongly 

 to the east, and crossed by a southerly or south-westerly 

 current. High gales, in certain localities where the 

 waves set upon a Hush, flat shore, drive the waters 

 fifteen to twenty feet beyond the usual mark. This 

 circumstance may partly explain the Arab's belief in a 

 regular Madd wa Jarr — ebb and flow — which Eastern 

 travellers always declare to have observed upon the 

 Tanganyika and Nyassa Lakes, and which Mr. Ander- 

 son believes to exist in the little Ngami. A mass of 

 water so large must be, to a certain extent, subject to 

 tidal influences ; but the narrowness of the bed from 

 east to west would render their effect almost unob- 

 servable. Mr. Francis Galton referred me for the ex- 

 planation of this phenomenon to a paper 1 On the 

 Seiches of Lakes,' by Colonel J. R. Jackson, F.R.G.S., 

 published in the 4 Journal of the R. G. S./ vol. iii. of 



