The boys endorsed the statement of previous travellers that rain and humidity are the chronic condition of Central Africa. They found the clouds a relief rather than otherwise, as the rays of the sun are excessively warm, especially in the middle of the day, when they become almost insupportable. The high elevation at which they were travelling made the nights very cold. An abundance of thick clothing prevented their suffering from the chilly nights, but their porters and attendants had no such protection, and were wretchedly miserable all the time the sun was below the horizon.
[Illustration: EFFECT OF A LONG RAIN IN AFRICA.--ANIMALS SEEKING SAFETY.]
While they were at dinner, on the second evening after leaving Foueira, the conversation naturally turned upon the peculiarities of the region they were traversing.
"It is only within the present century," said the Doctor, "that we have definitely ascertained the geography of the interior of Africa. It was formerly supposed to be a mountainous region, sloping steadily away to the sea; and there was a tradition, as I have before told you, of the great rivers of Africa rising near each other and flowing in different directions, as the water is carried from the roof of a house.
"The explorations of Livingstone, Burton, Speke, Du Chaillu, Cameron, Baker, and others have demonstrated that the centre of the continent is a vast plateau, or table-land, elevated from two thousand to four thousand feet above the level of the sea. There are mountains in the centre, and in various parts of this plateau, eight or ten thousand feet high, and there is a rocky rim or edge nearly all the way around it, with occasional openings, through which the rivers find their exit."
Frank was pushing aside his tea-saucer, when the Doctor paused and told him to invert it on the table.
"Now," he continued, "you have in that tea-saucer, bottom upward, a fairly good picture of the interior of Africa. Let the table where it is lying represent the ocean surrounding the continent. The rim on which it rests when right-side up is the mountainous ridge enclosing the central plateau, and the space in the centre is the plateau, or table-land. The slope from the ridge to the edge of the saucer is the strip of land around the coast. It varies greatly, as it is very narrow in some parts of the continent and quite broad in others. If you break a few notches at irregular intervals along the ridge you will indicate the depressions where the rivers pass from the equatorial basin to the great ocean."