midnight
The two boys , with Captain Wiltsey , had made their way to a position near the spillway , below the great Gatun Dam . It was an intensely dark night , though off to the west were distant flashes of lightning now and then , telling of an approaching storm . In the darkness the boys moved cautiously about , planting their cameras and flashlight batteries to give the best results . They had had to work quickly to get matters in shape before midnight . Fortunately they were not delayed by lack of magnesium powder , a large quantity having been found in one of the laboratories . This was quickly made up into flashlight cartridges , to be exploded at once , or in a series , by means of a high voltage storage battery . The moving picture cameras had been put in place , Blake to work one and Joe the other , while the automatic , which was operated by clockwork , once the trigger-string was broken , also setting off the continuous flashlight , was set between the two boys , to command a good view of the dam , and of whoever should approach to blow it up .