about midnight
Commence operations at once , '' was the order that was flashed back after congratulations had been extended . As it was too late to do anything more that night , the boys decided to commence work on the derelict in the morning . After a hearty supper they retired to bed in the chassis of the aeroplane , all as tired out as it is possible for healthy boys to be . Nevertheless , Frank , who always -- as he put it -- `` slept with one eye open , '' was awakened at about midnight by a repetition of the noise of the mysterious airship . There was no mistaking it . It was the same droning `` burr '' they had heard on the night following their discovery of the flaming mountain . Waking Harry , the two lads peered upward and saw the stars blotted out as the shadowy form of the air-ship passed above them -- between the sky and themselves .