"Perhaps she has already," suggested Ned, as the crew began clearing the submarine's deck.
"No, we lie too low in the water for that. Well, now we can start our underwater observations of current trends."
It did not take long, once she started, for the M. N. 1 to go down. Just as the sun sank below the horizon, and while the smudge of smoke was becoming more distinct, the waves closed over the steel deck of the submarine. Half an hour later she was nearly a quarter of a mile below the surface, resting on the bottom of the sea again.
On this trip Tom did not go to any such depths as he did on his former voyage in the Advance. Not that the reconstructed submarine was not capable of it, for she was even stronger than when first built. But the wreck they were seeking did not lie in so great a depth of water, and there was no need of running useless risks.
"Well," remarked Ned, when they came to a stop, "I don't believe any one will find us here."
"Not an ordinary diver, at any rate," Tom agreed. "And after supper I'm going to have another go at the currents."
The meal was served as usual, and a very good one it was, considering the fact that not as many supplies could be carried in the rather limited space of a submarine as may be transported in an ocean liner. Then, as it was still early, Tom and Ned, with the help of some of the officers, got ready for a new series of experiments.
The big searchlight was set aglow, and, going out on the ocean bed in diving suits, Tom and his friends dropped on the sand various weighted objects.
These were made in the shape of the hull of a steamer, and in proportion. Once they were on the sand, an iron rod was thrust into the ocean bed near each object.
"Now," remarked Tom, as they all went into the submarine again, "we'll let them drift until morning. Then we'll make new calculations. I think we'll arrive at some results, too."