It is a relief to turn from the icy north to the tropical climate of Central Africa, where Mungo Park had disappeared in 1805. The mystery of Timbuktu and the Niger remained unsolved, though more than one expedition had left the coast of Africa for the "mystic city" lying "deep in that lion-haunted inland." Notwithstanding disaster, death, and defeat, a new expedition set forth from Tripoli to cross the great Sahara Desert. It was under Major Denham, Lieutenant Clapperton, and Dr. Oudney. They left Tripoli in March 1822. "We were the first English travellers," says Denham, "who had determined to travel in our real character as Britons and Christians, and to wear our English dress: the buttons on our waistcoats and our watches caused the greatest astonishment." It was the end of November before they were ready to leave the frontier on their great desert journey. The long enforced stay in this unhealthy border town had undermined their health; fever had reduced Denham, Dr. Oudney was suffering from cough and pains in his chest, Clapperton was shivering with ague--a state of health "ill-calculated for undertaking a long and tedious journey." A long escort of men and camels accompanied them into the merciless desert, with its burning heat and drifting sands--"the Sea of Sahara" as the old cartographer calls it. December found them still slowly advancing over the billowy sand, deeply impressed and horrified at the number of slave skeletons that lay about the wind-swept desert. The new year brought little relief. "No wood, no water," occurs constantly in Denham's journal. "Desert as yesterday; high sandhills." Still they persevered, until, on 4th February 1823, they were rewarded by seeing a sheet of water, "the great Lake Tchad, glowing with the golden rays of the sun in its strength." Was this, after all, the source of the Niger? Its low shores were surrounded with reedy marshes and clumps of white water-lilies, there were flocks of wild ducks and geese, birds with beautiful plumage were feeding on the margin of the lake, pelicans, cranes, immense white spoonbills, yellow-legged plover--all were dwelling undisturbed in this peaceful spot. And this most remarkable lake lay eight hundred feet above the Atlantic, between the watersheds of Nile, Niger, and Congo. But Lake Tchad was not their goal; they must push on over new country where no European had been before. A fortnight later they reached Kukawa, the capital of Bornu, once a great Mohammedan empire. "We were about to become acquainted with a people who had never seen or scarcely heard of a European," says Denham, "and to tread on ground, the knowledge and true situation of which had hitherto been wholly unknown. We advanced towards the town of Kuka in a most interesting state of uncertainty, whether we should find its chief at the head of thousands, or be received by him under a tree, surrounded by a few naked slaves."