th of the Pandora was greater than had been supposed. "I have
many large interests," he went on, rather pompously, "and they need
looking after; especially if I undertake anything so extra hazardous as
a submarine trip."

"Yes, there always is some danger," admitted Tom. "But then there is
danger walking along the street."

"Oh, there's no danger with Tom Swift!" exclaimed Mr. Damon. "I've
been under the sea and above the clouds with him, and, bless my
rainbow! he always brought us safe home."

"And I'll try to do the same this time," said the young inventor.

Busy days followed for Tom Swift and his friends. The force at work on
the submarine turned night into day to rush her completion, and in due
season she was set afloat in the dry dock basin and formally
rechristened the M. N. 1.

Mary blushed as she gave the boat her new name, and there was a little
cheer from the group of workmen gathered at the dock. There was no
launching in the real sense of the word, since as the Advance that
ceremony had been gone through with for the undersea craft.

She had been greatly changed interiorly and outwardly. Her skin, or
plates, having been doubled and strengthened. For Tom proposed to go to
a much greater depth than ever before.

In addition to using the submarine herself in a search for the gold on
the Pandora, Tom had installed on board some new kinds of diving
apparatus and also a diving bell. If one would not serve, the other
might, he reasoned.

"Well, Tom," remarked his aged father the night before they were to
start on the trial trip, "I understand you have practically rebuilt the
Advance."

"Yes; and I think she's a much better craft, too, Father."

"Glad to hear that, Tom. Of course you kept the gyroscope rudder
feature?"

"No, I didn't," replied Tom. "If I had left that installed it would
have meant carrying a smaller diving bell, and I think that last will
be more useful than the gyroscope. I put in a set of double-acting
depth rudders instead."

Mr. Swift shook his head.

"I'm sorry for that, Tom," he remarked. "There's nothing like the
gyroscope rudder in a tight pinch--say when there's a storm. And for
holding the boat steady, if you have to make a sudden turn under water,
to avoid an obstruction you come upon unexpectedly, a gyroscope can't
be improved on. It holds you steady and prevents your turning turtle."

"I've put side fin-keels to correct that," Tom explained.

But still his father