"That's just what we have yet to ascertain," the young inventor replied. "So far our conclusions have been arrived at merely from surface data. Now we've got to go below."
"And play with bits of cork there?" asked Mr. Damon.
"No, we'll have to use something heavier than cork," Tom said. "We'll probably use weights, and see how far they move along the bottom in a given time. But we have established one thing, and I begin to have hopes now that we may locate the Pandora."
The remainder of the day was spent in various ways aboard the submarine, which continued to float idly on the waves.
It was toward evening, when the red, setting sun gave promise of a fair day on the morrow that the submarine's deck lookout approached Tom, and, waiting until he had the attention of the young inventor, reported:
"There is a smudge of smoke dead astern, sir."
"Is there?" exclaimed Tom. "Let me have the glasses."
He took them from the lookout and made a long and careful study of the slight, black smudge which was low down on the horizon.
"A steamer," decided Tom, "and coming on fast. We'll go below!" he added. "Please make ready," he said to the officer in charge.
"What's up, Tom?" asked Ned, as his chum gathered up the papers on which he had been figuring on an improvised table set under an awning on deck.