NATURE 



353 



THURSDAY, AUGUST iS 



THE CENTRAL AFRICAN LAKES 

 To the Cent! al African Lakes and Back : The Narra- 

 Hve of the Royal Geographical Socie/y's East African 

 Expedition, 1S78-80. By Joseph Thomson, F.R.G.S. 

 Two vols. (London : Sampson Low and Co., 1881.) 



OUR readers must be fimiliar with the leading features 

 of the remarkable Expedition which set out at the 

 end of 187S under the leadership of Mr. Keith Johnston, 

 and returned in 1880 under that of Mr. Joseph Thomson. 

 We have already told the story of the E.xpedition pretty 

 fully, and Mr. Thomson himself described in these pages 

 the main points in the geology of the Expedition which he 

 traversed. Mr. Thomson was a very young and inexpe- 

 rienced man when, by the sad death of his accomplished 

 chief, the command of the Expedition devolved upon him, 

 just after it had got over the initial difficulties of the 

 coast region and entered on the great tableland which 

 occupies the greater part of the African area. Mr. 

 Thomson showed himself at once equal to the emergency, 

 and succeeded in winning a reputation that is likely to 

 prove fruitful of good results both for himself and for 

 African geology. He has been equally successful in 

 telling the story of his journey. He writes in quiet and 

 simple, but effective, style, his pages are full of incident 

 and information of great interest, and he has a sense of 

 humour and a love of fun which are not only of service 

 to him under trying conditions, but which render his 

 book light and pleasant reading. After seasoning them- 

 selves by a little trip to Usambarra, Messrs. Johnston and 

 Thomson (the latter geologist to the Expedition), at the 

 head of 150 men, left Dar-es-Salaam in May, 1879, for the 

 north end of Lake Nyassa, A month later Mr. Johnston 

 died at Behobeho, to the north of the Rufiji, just when the 

 mountainsthat bound the plateauhadbeenreached, through 

 the usual difficulties attending African travel, partly arising 

 from the nature of the country, partly from the natives, 

 and partly from the men who formed the Expedition ; but 

 Mr. Thomson overcame them all with more than usual 

 tact, and with unprecedented success. After a short rest 

 at Lake Nyassa the route was resumed over the pre- 

 viously untraversed country between Nyassa and the 

 south end of Lake Tanganyika. Leaving most of his 

 men here, Mr. Thomson, with a small contingent, pro- 

 ceeded up the rugged west side of the lake to the famous 

 river, about whose course Messrs. Cameron and Stanley 

 gave such inconsistent accounts — the Lukuga. Mr. 

 Thomson' s observations on this river are of great value 

 in connection with African hydrography. He found that 

 Cameron and Stanley were both right. At Cameron's 

 visit, what little current existed was towards the lake; 

 Stanley, later on, found a distinct current setting 

 from the lake, and prophesied that in a short time the 

 barrier of vegetation across the river not far from its 

 mouth would be carried away, and the Lukuga would 

 carry the waters of Tanganyika in a full stream to the 

 Lualaba-Congo. j And this, Mr. Thomson found, had 

 actually come to pass ; he saw the Lukuga as a broad, 

 swift effluent from Lake Tanganyika. When, however, 

 he returned two months later, he found that the strength 

 Vol. XXIV. — No. 616 



of the current had considerably decreased, as had also 

 the volume of the river. Mr. Thomson discusses the in- 

 teresting problem of the Tanganyika at some length, and 

 with great intelligence, as well as with the knowledge of 

 a trained and practical geologist. He refers to the facts 

 observed by previous travellers as well as himself, as to 

 the rise and fall of the level of the lake, the hydro- 

 graphy of the neighbouring country, &c., and concludes 

 as follows : — 



"With these facts before us the necessity of Tanganyika 

 having a regular outlet is not so apparent as it seems to 

 have been to Cameron. Neither need we, like Stanley, 

 invoke the aid of great convulsions to account for the in- 

 terruption or intermittency of the outflow. The pheno- 

 mena are sufficiently accounted for by the facts I have 

 enumerated, viz. (first), that since tlie Arabs settled at 

 Ujiji till within the last five years there has been no 

 very marked rise in the level of the lake ; (second), that 

 the rapid rise of the lake after that time was due to un- 

 usually wet seasons ; (third), that the normal rainfall is 

 less than fifty inches in the year ; (fourth), that Tangan- 

 yika drains a remarkably small area of land, and has only 

 a few insignificant rivers, torrents, and streams falling 

 into it ; and (fifth), that the volume of water passing out 

 by the Luluiga is diminishing so rapidly as to be markedly 

 noticeable in two months, even in the course of the rainy 

 season, so that quite possibly the next traveller may arrive 

 to find little or no water leaving the lake. These con- 

 siderations, then, as well as all my inquiries and observa- 

 tions, lead me to conclude (first), that under normal cir- 

 cumstances the rainfall and evaporation nearly balance 

 each other ; (second), that many years ago a series of 

 unusually dry seasons reduced the level of the lake below 

 that of its outlet ; (third), that it remained sufficiently 

 long without circulation to become charged with salts, 

 which have given the water a markedly peculiar and un- 

 pleasant taste, unlike that of ordinary fresh water, and 

 also an exceptional power of corroding metal and leather ; 

 (fourth), that unusually wet seasons set in some five or 

 six years ago, raising the level of the lake ; (fifth), that it 

 rose above its normal level, owing to the formation of a 

 barrier in the bed of the Lukuga by rapid vegetable 

 growth, and the depositing of alluvium by the small 

 streams descending from the slopes on either side ; and 

 (sixth), that the lake having once overflowed the barrier, 

 soon removed it entirely, thus regaining its original 

 channel and level." 



After a short stay with the hospitable and intelligent 

 missionaries at Mtowa, to the north of the Lukuga outlet, 

 and paying a visit to Ujiji, Mr. Thomson set out to make 

 his way back through terrible Urua, where Cameron suf- 

 fered so much. Here he had to undergo the worst recep- 

 tion he met with during his whole journey ; every pos- 

 sible obstacle was placed in his way, every opportunity- 

 was taken to insult him and steal his goods, even the 

 very blanket from beneath him when asleep ; and it was 

 only by the greatest self-restraint and tact that fighting 

 was avoided and he and his men escaped with their lives. 

 This they were only too glad to do, just before they 

 reached the goal of the expedition, the river Lukuga. 

 Returning to Mtowa, a passage was obtained in INIr. 

 Hore's boat to the south end of the lake. Here Mr. 

 Thomson picked up his men and set out on the return 

 journey. He had intended to go east through Usanga 

 and by the upper waters of the Rufiji, but as the natives 

 were at war this would have been dangerous. So he 

 went north by the east side of Tanganyika, taking occa- 

 sion to have a good look at the mysterious Lake Hikwa^ 



