John Hanning Speke questions about the height and extent of the lake could not be answered easily. Speke's eyes were still bothering him and he only saw a small part of the southern end of the lake and his view was blocked by islands in the lake so he could not judge the size of the lake well. However, Speke did estimate the elevation of Lake Victoria at 4000 feet by observing the temperature at which water boiled at that level. (This lake's being substantially higher than Lake Tanganyika did make it a more likely candidate for the source of the Nile.) From
John Hanning Speke tried to remove it with a knife. Unable to rent the larger vessel from the Arab, Speke returned. The pair were unable to explore Lake Tanganyika properly and they initially misunderstood that a river flowed out of it from the north side. A few weeks later Sidi Mubarak Bombay confirmed via locals that the river flowed into the lake; however, since neither man actually saw this river, this remained a source of speculation. They had also heard of a second lake to the north-east, and in May 1858, they decided to explore it on the way back to the coast.