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.
The young inventor was not a little nervous as he prepared to press the button this time. It was a heavier charge than any used that day, though the same quantity had been fired on other occasions with safety. But he was not going to hesitate.
Coincident with the pressure of Tom's fingers there seemed to be a veritable earthquake. The ground swayed and rocked, and a number of the spectators staggered back. It was like the blast of a hundred thunderbolts. The gun shook as it recoiled from the shock, but the wonderful disap-
