town below.

But, through great pipes that led to the drinking system, though they
were unseen, thundered immense streams of solid water, reducing by as
much as the engineers were able the pressure on the concrete wall.

Tom and Ned, in the Humming Bird, took a flight out to the dam shortly
after breakfast, when the steel men were putting a few finishing
touches to the gun carriage, ready for the test that was to take place
about noon.

"It doesn't look as though it would burst," observed Ned, as the
aircraft hovered over the big artificial lake.

"No," agreed Tom. "But I suppose the engineers want to be on the safe
side in case of damage suits. I want to take a look at the place where
the other valley comes up to this at right angles."

He steered his powerful little craft in that direction, and circled low
over the spot.

"A bursting projectile, about where that big white stone is, would do
the trick," murmured Tom.

"What trick?" asked Ned, curiously.

"Oh, I guess I was talking to myself," admitted Tom, with a laugh. "I
may not have to do it, Ned."

"Well, you're talking in riddles today, all right, Tom. When you get
ready to put me wise, please do."

"I will. Now we'll get back, and fire our first long shot. I do hope I
make a record."

There was much to be done, in spite of the fact that the foreman of the
steel workers assured Tom that all was in readiness. It was some time
that afternoon when word was given for those who wished to retire to an
improvised bomb-proof. Word had previously been sent down the valley so
that no one, unless he was looking for trouble, need be in the vicinity
of the gun, nor near where the shots were to land.

Through powerful glasses Tom and Ned surveyed the distant mountain that
was to be the target. Several great squares of white cloth had been put
at different bare spots to make the finding of the range easy.

"I guess we're ready now," announced the young inventor, a bit
nervously. "Bring up the powder, Koku."

"Me bring," exclaimed the giant, calmly, as he went to the bomb-proof
where the powerful explosive was kept.

The great projectile was in readiness to be slung into the breech by
means of the hoisting apparatus, for it weighed close to two tons. It
was carefully inserted under Tom's supervision. It carried no bursting
charge, for Tom's first shot was merely to establish the extreme range
that his cannon would shoot.

"Now the powder," called the young