ts may happen,
and if the Mars can't go on, after a little damage like this, what is
going to happen when she's fired on by a hostile ship? Of course I'm
going on!"

"Bless my necktie!" ejaculated the odd man.

"That's the way to talk!" exclaimed Lieutenant Marbury. "I'm with you."

There really was very little danger in proceeding. The Mars was just as
buoyant as before, for more gas had been automatically made, and forced
into the uninjured compartments of the bag. At the same time enough
sand ballast had been allowed to run out to make the weight to be
lifted less in proportion to the power remaining.

True, the speed would be less, with two propellers instead of three,
and the craft would not steer as well, with the torn ends of the gas
bag floating out behind. But this made a nearer approach to war
conditions, and Tom was always glad to give his inventions the most
severe tests possible.

So, after a little while, during which it was seen that the Mars was
proceeding almost normally, the matter of discharging the guns was
taken up again.

The weapons were all ready to fire, and when Tom had attached the
pressure gauges to note how much energy was expended in the recoil, he
gave the word to fire.

The two big weapons were discharged together, and for a moment after
the report echoed out among the cloud masses every soul on the ship
feared another accident had happened.

For the big craft rolled and twisted, and seemed about to turn turtle.
Her forward progress was halted, momentarily, and a cry of fear came
from several of the members of the crew, who had had only a little
experience in aircraft.

"What's the matter?" cried Ned. "Something go wrong?"

"A little," admitted Tom, with a rueful look on his face. "Those
recoil checks didn't work as well in practice as they did in theory."

"Are you sure they are strong enough?" asked Lieutenant Marbury.

"I thought so," spoke Tom. "I'll put more tension on the spring next
time."

"Bless my watch chain!" cried Mr. Damon. "You aren't going to fire
those guns again; are you, Tom?"

"Why not? We can't tell what's the matter, nor get things right
without experimenting. There's no danger."

"No danger! Don't you call nearly upsetting the ship danger?"

"Oh, well, if she turns over she'll right herself again," Tom said.
"The center of gravity is low, you see. She can't float in any position
but right side up, though she may turn over once or twice."

"