第49章

"Over eight miles!" declared one grizzled officer; "and that with only a practice charge.What will happen when he puts in a full one?'

"I don't know," answered a friend.

Tom soon showed them.Quickly he called for another projectile, and it was inserted in the gun.Then the powder began to come up the hoist.Meanwhile the young inventor had assured himself that the gun was all right.Not a part had been strained.

This time, when Tom pressed the button there was such a tremendous concussion that several, who were not prepared for it, were knocked back against their neighbors or sent toppling off their chairs or benches.And as for the report, it was so deafening that for a long time after it many could 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."Icongratulate 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.

Consequently, the flatter the trajectory the farther it will go.Tom's object, then, was to flatten the trajectory, by lowering the muzzle of the gun, in order to attain greater distance.

"If this doesn't do the trick, we'll try it with the muzzle a bit lower, and with a trifle more powder," he said to Ned, as he was about to fire.