she went to four hundred, and
when the hand on the gauge showed four hundred and fifty there was a
tense moment. If anything went wrong now there would be serious trouble.

But Tom Swift and his men had done their work well. The M. N. 1 stood
the strain, and when the gauge showed four hundred and ninety feet Mr.
Damon gave a faint cheer.

"Bless my apple dumpling, Tom!" he replied, "this is wonderful."

"Oh, we've been deeper than this," replied the young inventor, "but
under different conditions. I'm glad to see how well she is standing
it, though."

Suddenly, as the needle pointer on the depth gauge showed five hundred
and two feet, there came a slight jar and vibration that was felt
throughout the craft.

"What's that?" suddenly and nervously cried Mr. Hardley. "Have we
struck something?"

"Yes, the bottom of the ocean," answered Tom quietly. "We are now on
the floor of the Atlantic, though several hundred miles, and perhaps a
thousand, from the treasure ship. We bumped the bottom, that's all,"
and as he spoke he brought the submarine to a stop by a signal to the
engine room.

And there, as calmly and easily as some of the masses of seaweed
growing on the ocean floor around her, rested the M. N. 1. It was a
test of her powers, and well had she stood the test, though harder ones
were in store for her.

And inside the submarine Tom and his party were under scarcely greater
discomfort than they would have been on the surface. True, they were
confined to a restricted space, and the air they breathed came from
compression tanks, and not from the open sky. The lights had to be
kept aglow, of course, for it was pitch dark at that depth. The
sunlight cannot penetrate to more than a hundred feet. But sunlight was
not needed, for the craft carried powerful electric lights that could
illuminate the sea in the immediate vicinity of the submarine.

"Are you going to stay here long?" asked Mr. Hardley, when Tom had
spent some time making accurate readings of the various instruments of
the boat. "Of course, I realize that you are the commander, but if we
don't get to the treasure ship soon some one else may loot her before
we have a chance. She's been given up as a hopeless task more than
once, but the lure of the millions may attract another gang."

"I want to stay here until I make sure that nothing is leaking and that
everything is all right," answered the young inventor. "This is a test
I have not given her sin