d not hear well.

But Tom, and those who knew the awful power of the big cannon, wore
specially prepared eardrum protectors, that served to reduce the shock.

"What is it?" called Tom to the wireless operator, who was receiving
the range distance from the marking ship.

"A little less than twenty-nine miles."

"We must do better than that," said Tom. "I'll use more powder, and try
one of the newer shells. I'll elevate the gun a trifle, too."

Again came that terrific report, that trembling of the ground, that
concussion, that blast of air as it rushed in to fill the vacuum
caused, and then the vibrating echoes.

"I think you must have gone the limit this time, Tom!" yelled Ned, as
he turned on the compressed air to blow the powder fumes and unconsumed
bits of explosive from the gun tube.

"Possibly," admitted Tom. "Here comes the report." The wireless
operator waved a slip of paper.

"Thirty-one miles!" he announced.

"Hurray!" cried Mr. Damon. "Bless my telescope! The longest shot on
record!"

"I believe it is," admitted the chief of the ordnance department. "I
congratulate you, Mr. Swift."

"I think I can do better than that," declared Tom, after looking at the
various recording gauges, and noting the elevation of the gun. "I think
I can get a little flatter trajectory, and that will give a greater
distance. I'm going to try."

"Does that mean more powder, Tom?" asked Ned.

"Yes, and the heaviest shell we have--the one with the bursting charge.
I'll fire that, and see what happens. Tell the zone-ship to be on the
lookout," he said to the wireless operator, giving a brief statement of
what he was about to attempt.

"Isn't it a risk, Tom?" his chum asked.

"Well, not so much. I'm sure my cannon will stand it. Come on now, help
me depress the muzzle just a trifle," and by means of the electric
current the big gun was raised at the breech a few inches.

As is well known, cannon shots do not go in straight lines. They leave
the muzzle, curve upward and come down on another curve. It is this
curve described by the projectile that is called the trajectory. The
upward curve, as you all know, is caused by the force of the powder,
and the downward by the force of gravitation acting on the shot as soon
as it reaches its zenith. Were it not for this force the projectiles
could be fired in straight lines. But, as it is, the cannon has to be
elevated to send the shot up a bit, or it would fall short of its mark