156 Notes on the Congo River . 
of the line. Those of the northern hemisphere 
swell with the “ summer rains of Ethiopia,” a fact 
known in the case of the Nile to Democritus of 
Abdera (5th cent, b.c.), to Agatharchidas of Cnidos 
(2nd cent, b.c.) to Pomponius Nida, to Strabo 
(xvii. 1), who traces it through Aristotle up to 
Homers “heaven-descended stream” and to Pliny 
(v. 10). For the same reason the reverse is the 
case with the two southern arteries ; their high 
water, with certain limitations in the case of the 
Congo, is in our winter. 
By the condition of their courses, all the four 
magnates are broken into cataracts and rapids at 
the gates where they burst through the lateral 
chains ; the Mosi-wa-tunya (smoke that thunders) 
of the Zambeze, and the Ripon Falls discovered by 
Captains Speke and Grant upon the higher Nile, 
are the latest acquisitions to geography, whilst the 
“Mai waterfall,” reported to break the Upper 
Congo, still awaits exploration. This accident of 
form suggests a division of navigation on the mari¬ 
time section and on the plateau-bed which, in due 
time, will be connected, like the St. Lawrence, by 
canals and railways. All but the Nzadi, and 
perhaps even this, have deltas, where the divided 
stream, deficient in water-shed, finds its sluggish 
way to the sea. 
The largest delta at present known is the Ni¬ 
gerian, whose base measures 155 direct geogra- 
