It is well known that trading stations for ivory have been established for about 500 miles up Petherick's branch. We must remember this fact when told that Gondokoro, in lat. 4 degrees N., is 2,000 feet above the sea, and lat. 4 degrees S., where the halt was made, is only a little over 2,000 feet above the sea. That the two rivers said to be 2,000 feet above the sea, separated from each other by 8 degrees of latitude, are one and the same river, may among some men be regarded as a startling statement. But we must restrain mere expressions of surprise, and take into consideration that this mighty and broad Lualaba is a lacustrine river broader than the Mississippi; that at intervals the body of water forms extensive lakes; then, contracting into a broad river, it again forms a lake, and so on, to lat. 4 degrees; and even beyond this point the Doctor hears of a large lake again north. We must wait also until the altitudes of the two rivers, the Lualaba, where the Doctor halted, and the southern point on the Bahr Ghazal, where Petherick has been, are known with perfect accuracy. Now, for the sake of argument, suppose we give this nameless lake a length of 6 degrees of latitude, as it may be the one discovered by Piaggia, the Italian traveller, from which Petherick's branch of the White Nile issues out through reedy marshes, into the Bahr Ghazal, thence into the White Nile, south of Gondokoro. By this method we can suppose the rivers one; for if the lake extends over so many degrees of latitude, the necessity of explaining the differences of altitude that must naturally exist between two points of a river 8 degrees of latitude apart, would be obviated. Also, Livingstone's instruments for observation and taking altitudes may have been in error; and this is very likely to have been the case, subjected as they have been to rough handling during nearly six years of travel. Despite the apparent difficulty of the altitude, there is another strong reason for believing Webb's River, or the Lualaba, to be the Nile. The watershed of this river, 600 miles of which Livingstone has travelled, is drained from a valley which lies north and south between lofty eastern and western ranges. This valley, or line of drainage, while it does not receive the Kassai and the Kwango, receives rivers flowing from a great distance west, for instance, the important tributaries Lufira and Lomami, and large rivers from the east, such as the Lindi and Luamo; and, while the most intelligent Portuguese travellers and traders state that the Kassai, the Kwango, and Lubilash are the head waters of the Congo River, no one has yet started the supposition that the grand river flowing north, and known by the natives as the Lualaba, is the Congo.