514 



DR. W. A. CUNNINGTON ON THE 



occasions and at ditlerent places only vary between 74-8^ and 

 74" 1°. Stuppers gives the temperature of the surface water as 

 oscillating between 25° and 28° C. (77°-82-4° F.) (176). Mar- 

 cpiardsen, however, quotes exactly 25*0° 0. (77° F.) as a mean 

 of 70 surface readings made by Jacobs. The latter was also 

 able to carry out deep water observations, to which Marquardsen 

 refers as follows : — " Unter 400 m. bis in die grossten Tiefen 

 liei»t dann eine fast homotherme Wasserschicht von 23' 15° bis 

 23-12° " (73-67°-73-61° F.) (Ill, p. 1)7). A less extended series of 

 water temperature observations was made in Nyasa* and also in 

 Victoria jS'vanza durini^- the Third T a ngaiiy ilva. Expedition, but 

 tlie figures are sufficient to show that there are no important 

 ditt'erences from the results obtained in Tanganyika. It is 

 obvious tliat the amount of water lost by evapoiution must be 

 very great in all these cases. 



As far as 1 am aware, there is lelatively little known con- 

 cerning the nature of the water in these African l[dves. They 

 are considered in general terms to be " fresh " t, but, except in 

 certain instances, no analyses liave been made, and the nature 

 and quantity of the salts dissolved in the water are nid^nown. 

 The information which is to hand legarding Tanganyika and 

 Kivu makes it clear that they difler from normal fresh waters, 

 and this dilference appears to be rellected (as will be shown in 

 due course) in the nature of the organisms they contain. T\ai- 

 ganyika water, while containing a relatively small ainonnt of 

 calcium salts, is unusually rich in salts of magnesium (176). 

 Lake Kivu is an extreme case, where the salinity is very high. 

 In this instance, salts of calcium appear to have been almost 

 entirely replaced by considerable amounts of sodium and 

 magnesium salts, the latter being quite excessive in quantity 

 (103). 



It is possible that the water of Tanganyika has somewhat 

 changed in nature within recent years, for most of the early 

 explorers agree that the water was brackish, or at least pecu- 

 liar " in taste. If the rather vague statements are to be relied 

 upon, this alteration in salinity is probably to be associated with 

 the question of the outflow of the lake. A period during which 

 the lake possessed no outlet would result in an accumulation of 

 salts producing brackish water, while a subsequent period with 

 a, regular outflow would diminish the quantity of saline matter 

 in solution. An examination of the available records suggests 

 that something of this kind has taken place, and it thus becomes 

 necessary to consider the wdiole subject of the outflow of Tan- 

 ganyika. 



This is not the place to discuss in detail all the evidence 



* Certain observations concerning Nyasa were made b}' Fiilleborn (83, p, 334 

 ct seq.). 



f Grogan, referring to Lake Edward, says :■ — ■" Althougli tlie water was salt, it 

 was drinkable" (91, p. 191). In tbe same coiiik ction Briglit remarks: — "The 

 water of Al))ert is drinkable, but not good " (55, ]). 138). 



