At first sight, it seems strange that Stanley should have selected this lake as the next scene of his explorations. He had previously, with Livingstone, explored thoroughly the upper half of it, and passed part way down the western side; Livingstone had been at the foot of it, and to crown all, Stanley had heard, before leaving Zanzibar, that Cameron had explored the entire southern portion, so that really there was nothing for him to do but follow a path which had been already trodden. To employ an expedition fitted out at so great a cost, and spend so much valuable time in going over old ground, seems an utter waste of both time and labor, especially when such vast unexplored fields spread all around him. But there was a mystery about Tanganika, which Stanley probably suspected Cameron had not solved, and which he meant to clear up. Here was a lake over three hundred miles long, with perhaps a hundred streams, great and small, running into it, and yet with no outlet, unless Cameron had found it, which he thinks he did. To find this was the chief object of the expedition Stanley and Livingstone made together to the north end of the lake. They had heard that the Rusizi River at that extremity was the outlet, but they found it instead a tributary. In fact, they proved conclusively that there was no outlet at the northern end. It therefore must be at the southern, and if so, it was the commencement of a river that would become a mighty stream before it reached the ocean. But no such stream was known to exist. The Caspian Sea has large rivers flowing into it, but no outlet, yet it never fills up. Evaporation, it is supposed, accounts for this. But the Caspian is salt, while the Tanganika is fresh water, and such a large body of fresh water as this was never known to exist without an outlet, and if it could be that evaporation was so great as to equal all the water that runs into it, it would not remain so fresh as it is.