"Catch the figure, Ned!" Tom cried.

"I have it!" was the answer. "Eighty thousand!"

"Good! And I can build a recoil check that will take up to one
hundred and twenty thousand pounds pressure. That ought to be
margin of safety enough. Now we'll try another shot."

The echoes of the first had hardly died away before the second
gun was ready for the test. That, too, was satisfactory, and then
the smaller ones were operated. These were not quite so
satisfactory, as the recoil developed was larger, in proportion
to their size, than Tom had figured.

"But I can easily put a larger hydrostatic check on them," he
said. "Now, we'll fire by batteries, and see what the total is."

Then began a perfect bombardment of the distant hillside,
service charges being used v, and explosive shells sent out so that
dirt, stones and gravel flew in all directions. Danger signs and
flags had been posted, and a cordon of Tom's men kept spectators
away from the hill, so no one would be in the danger zone.

The young inventor was busy making some calculations after the
last of the firing had been completed. Koku was packing up the
unfired shells, and Mr. Damon was blessing his ear-drums, and the
pieces of cotton he had stuffed in to protect them, when a tall,
erect man was observed strolling over the fields in the direction
of the guns.