But the noise of the shots had evidently frightened the long-eared animal, and he was in no mood for stopping, now that he had once started.  It was not until some of the workmen ran out from the group where they had gathered to watch Tom’s test, and got in front of Boomerang, that they succeeded in bringing him to a halt.

Eradicate climbed slowly down from the seat, and limped around until he stood in front of his pet.

“Yo’—­yo’re a nice one, ain’t yo’?” he demanded in sarcastic tones.  “Yo’ done enough runnin’ in a few minutes fo’ a week ob Sundays, an’ now I won’t be able t’ git a move out ob ye!  I’se ashamed ob yo’, dat’s what I is!  Puffickly ashamed ob yo’.  Go ‘long, now, an’ yo’ won’t git no oats dish yeah day!  No sah!” and, highly indignant, Eradicate led the now slowly-ambling mule off to the stable.

“I won’t shoot again until you have him shut up, Rad!” laughed Tom.  “I didn’t know you were so close when I set off those guns.”

“Dat’s all right, Mass a Tom,” was the reply.  “I done called t’ you t’ wait, but yo’ didn’t heah me, I ’spects.  But it doan’t mattah, now.  Shoot all yo’ laik, Boomerang won’t run any mo’ dis week.  He done runned his laigs off now.  Shoot away!”

But Tom was not quite ready to do this.  He wanted to see what effect the first shots had had on his aerial warship, and to learn whether or not the newly devised recoil check had done what was expected of it.

“No more shooting right away,” called the young inventor.  “I 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.”