522 



science:. 



[Vol. IX., No. 335 



they flow slowly towards the west coast, unob- 

 structed by rapids or cataracts until they reach 

 the western rim of the plateau. Here the mighty 

 Kongo and the smaller river rush down its steep 

 side in roaring rapids and cataracts. 



The character of this district depends to a great 

 extent upon the meteorological phenomena, par- 

 ticularly on the amount of rainfall. North and 

 south of the district included between latitudes 

 30'^ north and 30*^ south, the aridity of the 

 climate, , which is due to the trade-winds, pro- 

 duces the vast deserts and steppes of the Sahara 

 and Kalahari. In the iDarts adjoining the equator 

 we find rainy and dry seasons interchanging. On 

 the west coast the climate is influenced by the 

 prevailing south-westerly winds, which tend to 

 lower the temperature, particularly as they blow 

 from the cold Benguela current. The isothermal 

 lines on the west coast approach the equator much 

 nearer than do those on the east coast. There 

 are two seasons, — the cool and foggy one, which 

 has no thunder-storms ; and the hot, rainy 

 season. The dry season begins towards the end 

 of May, and lasts, in the southern parts until 

 August, in Loango until the middle of October. 

 Farther north, at Gabun, the dry season lasts from 

 June until the middle of September, but slight 

 showers of rain occur in all months. During this 

 season a whitish haze obscures the sun : early 

 in the morning thick fogs cover the land, and the 

 dew is very plentiful. The fog produces a driz- 

 zling rain, which is of great importance for the 

 development of the vegetation. While the west 

 coast south of the equator has little rain, the east 

 coast, which is under the influence of the south- 

 easterly trade-winds, is very damp. From May 

 until October south-westerly winds prevail on 

 this coast, while later on the trade- winds are 

 blowing. The latter come from the warm Mo- 

 zambique current, and are saturated with vapor, 

 which is precipitated on the mountain-ranges of 

 the east coast. Throughout the interior, summer 

 rains prevail, but near the tropic of Capricorn the 

 amount of rain is decreasing. Owing to the 

 humidity of the climate, the rivers are very numer- 

 ous, and carry great volumes of water. The 

 water jiheds of the whole district are very indis- 

 tinct ; the head waters of the Welle and Nile, 

 and those of the Sankuru-Kasai and the Zam- 

 bezi systems, being in close proximity, and not 

 separated by elevations. The same is probably 

 the case between the Welle and Shari, and until 

 quite recently we did not know whether the Welle 

 belonged to the Kongo or to the Tsade system. 

 The swamps and' lakes at the head of the 

 Kasai probably form a bifurcation between that 

 river and the Zambezi : according to Livingstone, 



the Dilolo Lake has a northern and a southern 

 outlet. 



The basin of Lake Bangweolo, and its outlet, 

 the Luapula, may be considered the source of the 

 Kongo, but the Lualaba is not inferior to it in 

 size : and after both rivers have joined, above 

 Nyangwe, the Kongo carries a great volume of 

 water. Below Stanley Falls the Lubilash and 

 Ubinji join it, and the river takes a westerly di- 

 rection. It is a characteristic feature of the Kongo 

 basin, west of longitude 35° east, that all rivers 

 take a westerly direction. In the north we have 

 the Welle-Makua, with its mighty tributaries the 

 Werre and Mbomu. This river, which very 

 probably empties into the Obangi, is one of the 

 most important tributaries of the Kongo ; but the 

 Sankuru system, which drains the southern por- 

 tion of the basin from longitude 15° to 35° east, 

 is not inferior to it. During the early time of 

 African travels, news reached us of the enormous 

 Lake Sankuru, which at last proved to be the 

 river system, which is now tolerably well known. 

 The Sankuru has its source near the foot of the 

 western slope of the East African highland, which 

 is indicated by the numerous lakes of the upper 

 Lualaba. As far as latitude 5° south it runs in a 

 northerly direction, and then turns to the west. 

 We are not sufficiently acquainted with the relief 

 and geology of Central Africa to understand why 

 the numerous rivers running south and north very 

 close to each other suddenly take a westerly turn 

 in this latitude. In the most central parts of the 

 Kongo basin, which is situated between the San- 

 kuru and Mbomu, this is the predominating dii-ec- 

 tion. Among the tributaries of the Sankuru, the 

 Lubilash, Kasai-Lulua, and Kuango, with its 

 tributaries, carry the greatest volume of water. 

 It seems that the north and south direction of the 

 western part of the Kongo is caused by its ap- 

 proach to the western watershed. It is doubtful 

 whether the Kadei and Nana, which are known 

 by Flegel's inquiries in Adamaua, belong to the 

 Kongo system. Here is the part of Africa which 

 is least known. The coast tribes, for fear of losing 

 the trade between the interior and the coast, pre- 

 vent explorers entering the continent, and no 

 traveller has reached that district either from the 

 Tsade basin or from the Welle-Nile watershed. 

 Besides this, the country east and west of the 

 Kongo above Stanley Falls is unknown, and so is 

 the territory north-east of the Victoria Nyanza. 



The central depression between the plateaus of 

 Central and North Africa is indicated by the 

 Shari and Bar-el-Arab. The upper part of the 

 former is still unknown, the south and north trib- 

 utaries of the latter having been the field of 

 Schweinfurth's, Junker's, Lupton's, and Emin's 



