nine o'clock in
the evening
All day Monday , Roger and his two helpers sweated to prepare for the plant 's first trial . Roger would let no one touch the engine but himself , but Ernest and Gustav puttered with the condenser and the pump and at dawn started the oil circulating through the absorber . All day long the burning desert sun poured its heat through the glass into the oil which caught and imprisoned it for Roger 's purpose , until the storage pit was full . Roger had set the time of trial as nine o'clock in the evening in order to prove the night as well as the day power of his plant . The Prebles appeared shortly before the hour . `` Everything O. K. ? '' asked Dick , with a creditable effort at being off-hand .