“So you’re going to give the guns a real test this time, is that it, Tom?” asked Ned, as he pushed back his plate, a signal that he had eaten enough.

“That’s about it.”

“But don’t you think it’s a bit risky out over the water this way.  Supposing something should—­should happen?” Ned hesitated.

“You mean we might fall?” asked Tom, with a smile.

“Yes; or turn upside down.”

“Nothing like that could happen.  I’m so sure that I have solved the problem of the recoil of the guns that I’m willing to take chances.  But if any of you want to get off the Mars while the test is being made, I have a small boat I can lower, and let you row about in that until—­”

“No, thank you!” interrupted Mr. Damon, as he looked below.  There was quite a heavy swell on, and the ocean did not appear very attractive.  They would be much more comfortable in the big Mars.

“I think you won’t have any trouble,” asserted Lieutenant Marbury.  “I believe Tom Swift has the right idea about the guns, and there will be so small a shock from the recoil that it will not be noticeable.”

“We’ll soon know,” spoke Tom.  “I’m going to get ready for the test now.”

They were now well out from shore, over the Atlantic, but to make certain no ships would be endangered by the projectiles, Tom and the others searched the waters to the horizon with powerful glasses.  Nothing was seen and the work of loading the guns was begun.  The bomb tubes, in the main cabin, were also to be given a test.

As service charges were to be used, and as the projectiles were filled with explosives, great care was needed in handling them.

“We’ll try dropping bombs first,” Tom suggested.  “We know they will work, and that will be so much out of the way.”

To make the test a severe one, small floating targets were first dropped overboard from the Mars.  Then the aerial warship, circling about, came on toward them.  Tom, seated at the range-finders, pressed the button that released the shells containing the explosives.  One after another they dropped into the sea, exploding as they fell, and sending up a great column of salt water.

“Every one a hit!” reported Lieutenant Marbury, who was keeping “score.”

“That’s good,” responded Tom.  “But the others won’t be so easy.  We have nothing to shoot at.”

They had to fire the other guns without targets at which to aim.  But, after all, it was the absence of recoil they wanted to establish, and this could be done without shooting at any particular object.

One after another the guns were loaded.  As has been explained, they were now made double, one barrel carrying the projectile, and the other a charge of water.

“Are you ready?” asked Tom, when it was time to fire.  Lieutenant Marbury, Ned and Mr. Damon were helping, by being stationed at the pressure gauges to note the results.