And now, in passing from Abu-Hammed to Kartoum, we have a grand secret of the Nile. For twelve hundred miles above its mouth that mysterious river receives no tributary on the right hand nor on the left. It may be traced like a ribbon of silver with a narrow fringe of green, winding in great folds through a hot and thirsty desert and under the full blaze of a sun that drinks its waters but returns nothing in the shape of rain. And man also exacts a heavy tribute for purposes of irrigation. Whence its supply? Look for a partial answer to the Atbara, whose mouth is in the east bank of the Nile, half way from Abu-Hammed to Kartoum. Here light begins to break on the exhaustless stores of the Nile. During the greater part of the year the Atbara is dry. Not a hopeful source of supply, you say at once. The sources of the Atbara are away off to the east in the mountains of Abyssinia, whose great buttresses are now visible from the Nile Valley, and whose projections push to the Red Sea and Indian Ocean. There also are a Lake Region and Nile sources, whose discovery by Bruce a century ago gave the scientific world quite a stir. His account of this Abyssinian country, so unique in physical features, social life, history, religion and ancient remains, read so much like romance that it was not believed. But Beke, De Cosson, James Bruce and the great Livingstone, have since verified all and given him his proper place among accurate observers and intrepid travellers. But it was Sir Samuel Baker, on his first journey up the Nile in 1861, who pointed out the importance of the Abyssinian rivers as Nile tributaries. He turned aside from his southward route and followed the dry bed of the Atbara for a double purpose. First, to watch the great annual flooding of this Nile feeder. Second, to enjoy the sport of capturing some of the big game, such as the elephant, rhinoceros, hippopotamus, giraffe and lion, known to abound in the thick jungles covering the lower slopes of the adjacent hills. [Illustration: PORTRAIT OF BAKER.]