After that an hour passed without anything unusual happening. Twice they passed river steamboats, one of them sweeping quite close to the houseboat.
"Why don't you put out more lights—want to be run down?" came the cry.
"Haven't any more lights," answered Tom, and then the two boats swept apart, so no more could be said.
A mile more was passed when Fred set up a cry:
"I see a light ahead, flashing from side to side," he said, and pointed it out.
"It is the acetylene gas lamp," ejaculated Harold Bird, "and it must be aboard of the launch!"
CHAPTER XI
WHAT THE ROCKETS REVEALED
All of those on board of the houseboat watched the flashing light with keen interest. That it came from the gasoline launch none of them doubted.
"If we can only catch up to them," said Tom. "And do it on the sly!"