nine o'clock
Several miles beyond was a point which projected out to sea ; they could see this plainly from Observation Hill , and during the last long trip inland they reached the sea beyond this cape . The shore line beyond was absolutely unknown to them , but it extended to the west as far as they could see , and when night set in the faint mist prevented them from judging how much farther it ran in that direction . Without proper instruments at sea , distance is always a difficult matter to judge , and the boys were constantly venturing guesses as to the distance traveled . The start was made shortly after nine o'clock , and it was now past six in the evening . `` How far do you think we have gone during the day ? '' was George 's question . The Professor made a mental calculation before replying .