want to
see how we made out with the first round. How did she check up, Ned?"

"Fine, as far as I can tell."

"Yes, indeed," added Lieutenant Marbury. "The recoil was hardly
noticeable, though, of course, with the full battery of guns in use, it
might be more so."

"I hope not," answered Tom. "I haven't used the full strength of the
recoil check yet. I can tune it up more, and when I do, and when I have
it attached to all the guns, big and little, I think we'll do the
trick. But now for a harder test."

The rest of that day was spent in trying out the guns, firing them with
practice and service charges, though none of the shells used contained
projectiles. It would not have been possible to shoot these, with the
Mars held in place in the midst of Tom's factory buildings.

"Well, is she a success, Tom?" asked Ned, when the experimenting was
over for the time being.

"I think I can say so--yes," was the answer, with a questioning look at
the officer.

"Indeed it is--a great success! We must give the Newton shock absorber
due credit."

Ned blushed with pleasure.

"It was only my suggestion," he said. "Tom worked it all out."

"But I needed the Suggestion to start with," the young inventor replied.

"Of course something may develop when you take your craft high in the
air, and discharge the guns there," said the lieutenant. "In a
rarefied atmosphere the recoil check may not be as effective as at the
earth's surface. But, in such case doubtless, you can increase the
strength of the springs and the hydrostatic valves."

"Yes, I counted on that," Tom explained. "I shall have to work out that
formula, though, and be ready for it. But, on the whole, I am pretty
well satisfied."

"And indeed you may well feel that way," commented the government
official.

The Mars was hauled back into the shed, and the roof slid shut over the
craft. Much yet remained to do on it, but now that Tom was sure the
important item of armament was taken care of, he could devote his
entire time to the finishing touches.

As his plant was working on several other pieces of machinery, some of
it for the United States Government, and some designed for his own use,
Tom found himself obliged to hire several new hands. An advertisement
in a New York newspaper brought a large number of replies, and for a
day or two Tom was kept busy sifting out the least desirable, and
arranging to see those whose answers showed they knew something of the
b