midnight
The canvas curtains at the sides of the aeroplane 's body were drawn up , forming a snug tent . The stove was set going and soup and canned meats and vegetables warmed and eaten by the light of a lantern . In the meantime Frank had discovered that the breakdown had been caused by a defect in the ignition apparatus which it would take some time to repair . Both he and Harry went to work on it after supper , however , and by midnight they had it adjusted . They were just preparing to turn in , the professor and Billy having wrapped themselves in their blankets some time before , when a sudden sound , breaking on the stillness of the Antarctic night , made them pause . Both boys strained their ears intently and the sound came once more . This time there was no mistaking it .