was not satisfied.

"I'd rather you had kept the gyroscope," he said, and the time was to
come when Tom Swift wished that himself.

But it was too late to make the change now, and so, with more than
usual confidence in his own designing abilities, the next day the young
inventor and his friends went aboard the M. N. 1 for the trial trip.

"You don't easily get seasick, do you?" Tom asked Mr. Hardley, as they
descended the hatchway into the interior of the craft.

"No, I'm considered a good sailor."

"Well, you'll need to be," went on Tom, with a smile. "Not that we are
likely to strike any rough water now, though the reports say a stiff
breeze is blowing in the bay. But when we once start for the West
Indies you are likely to experience a new sensation. I've known
sailors who never had any qualms, even in terrible storms, to get ill
in a submarine when she went through only a small blow. The motion is
different from that on a surface boat."

"I can imagine so," returned Mr. Hardley. "But I'll be thinking of the
millions in gold on the Pandora, and that will keep my mind off being
seasick."

"Let us hope so," murmured Tom.

He gave the word, they all descended, the hatch covers were closed
down, and the M. N. 1 was ready to start on a trial trip.

CHAPTER VIII

THE MUD BANK

"What's that noise?" asked Mr. Hardley.

Mr. Hardley, Tom Swift, Mr. Damon, Ned Newton, Koku, and one or two
navigating officers of the craft, were gathered in the operating cabin
of the M. N. 1.

"That's water being pumped into the tanks," explained Tom. "We are now
going down. If you'll watch the depth gauge you can note our progress."

"Going down, are we?" remarked Mr. Hardley. "Well, it's interesting to
say the least," and he observed the gauge, which showed them to be
twenty feet under the surface.

"Bless my hydrometer, but he's got nerve for a first trip in a
submarine! He's all right, isn't he?" whispered Mr. Damon to Tom.

"Well, I'm glad to see he isn't nervous," remarked Tom, honest enough
to give his visitor credit for what was due him. And indeed many a
person is nervous going down in a submarine for the first time. "Still
we can't go more than thirty feet down in this water," went on Tom. "A
better test will be when we get about five hundred feet below the
surface. That's a real test, though as far as knowing it is concerned,
a person can't tell ten feet from ten hundred in a submarine under
water, unless