The colored man prepared a simple supper for Mr. Henderson, and afterward got himself a meal. When the dishes were cleared away the old man, who had noted with smiles the anxious glances Jack and Mark were casting about the strange room, said:
"I suppose you boys would like to ask lots of questions."
"I'd like to know what all this machinery is for," spoke Jack.
"And what is behind that door," Mark went on, indicating the much-locked portal.
"I knew it!" exclaimed the old man. "I knew it! Now if I tell you will you promise to keep it a secret until I give you leave to speak?"
Of course the boys promised eagerly.
"Do you think you have rested enough now to take a look inside?" the inventor asked, nodding toward the locked door.
"Sure!" exclaimed Jack.
"Then put on your coats and trousers and I'll introduce you to my pet."
Wonderingly, the boys followed him. It took nearly a minute to unfasten the various bolts and bars, but at last the portal swung open. The place was dimly lighted by a single big lamp, but in the glare of it the boys caught sight of a strange, weird object. It looked like an immense cigar, and swayed slowly back and forward. It seemed to be covered with a net-work of cords. On the ground beneath it was what seemed to be a good-sized boat, with a large cabin amidships.