 Speke went on a 47-day side trip that was 452 miles up and down in which he took 34 men with Bombay and Mabruki as his captains and on 30 July 1858 became the first European to see Lake Victoria and the first to map it.It was this lake that eventually proved to be the source of the River Nile.However, much of the expedition's survey equipment had been lost at this point and thus vital questions about the height and extent of the lake could not be answered easily.