ance over other types of
submarines. Well, another week and we will be ready for the test."

"Have you known Mr. Berg long, dad?"

"Not very. I met him in Washington when I was in the patent office. He
was taking out papers on a submarine for his firm at the same time I
got mine for the Advance. It is rather curious that he should come all
the way here from Philadelphia, merely to see if I was going to
compete. There is something strange about it, something that I can't
understand."

The time was to come when Mr. Swift and his son were to get at the
bottom of Mr. Berg's reasons, and they learned to their sorrow that he
had penetrated some of their secrets.

Before going to bed that night Tom and Mr. Sharp paid a visit to the
shed where the submarine was resting on the ways, ready for launching.
They found Mr. Jackson on guard and the engineer said that no one had
been around. Nor was anything found disturbed.

"It certainly is a great machine," remarked the lad as he looked up at
the cigar-shaped bulk towering over his head. "Dad has outdone himself
this trip."

"It looks all right," commented Mr. Sharp. "Whether it will work is
another question."

"Yes, we can't tell until it's in the water," con ceded Tom. "But I
hope it does. Dad has spent much time and money on it."

The Advance was, as her name indicated, much in advance of previous
submarines. There was not so much difference in outward construction as
there was in the means of propulsion and in the manner in which the
interior and the machinery were arranged.

The submarine planned by Mr. Swift and Tom jointly, and constructed by
them, with the aid of Mr. Sharp and Mr. Jackson, was shaped like a
Cigar, over one hundred feet long and twenty feet in diameter at the
thickest part. It was divided into many compartments, all water-tight,
so that if one or even three were flooded the ship would still be
useable.

Buoyancy was provided for by having several tanks for the introduction
of compressed air, and there was an emergency arrangement so that a
collapsible aluminum container could be distended and filled with a
powerful gas. This was to be used if, by any means, the ship was
disabled on the bottom of the ocean. The container could be expanded
and filled, and would send the Advance to the surface.

Another peculiar feature was that the engine-room, dynamos and other
apparatus were all contained amidships. This gave stability to the
craft, and also e