"To lessen the shock to our ear drums," answered Paul. "It is the concussion, that is, the rushing back of air into the vacuum caused by the shot, that does the damage. By opening your mouth you equalize the air pressure on the inside and the outside of your ear drums, just as you do when you go through a river tunnel. When there is a partial vacuum outside your ear, the air inside you presses the drum outward, and by opening your mouth--or by swallowing you make the pressure equal. Sometimes the pressure outside is greater than the pressure inside, and you must also equalize that before you can be comfortable." "But that wasn't why you stood on your toes," Alice said. "No; we did that to have less surface of our bodies on the ground so the vibration would be less. If one could leap up off the earth at the exact moment a shot was fired it would be much better, but it is hard to jump at the right instant, and standing on one's toes is nearly as good. Then you present only a comparatively small point which the vibrations of the earth, caused by the explosion of the gun, can act upon." "That's a good thing to remember," Estelle said. "Are they going to fire again?" "It looks so," observed Russ. "But if they knock away too much of the hill there won't be any left for the pictures to-morrow." "I believe they want to make the top of the hill flat," said Paul. "They are going to have some sort of hand-to-hand fight on it after the Unionists capture it," he went on. "I heard Mr. Pertell speaking of it." "There goes another!" cried Alice, as she saw the same preparations as before and one man standing near the gun to pull the lanyard, which, by means of a friction tube, exploded the charge. Once more the projectile shot out and, burying itself in the soft dirt of the hill, threw it up in a shower. "That'll save me a lot of work!" exclaimed a voice behind the young people, and, turning, they saw Sandy Apgar smiling at them. "That's a new way of plowing," he went on. "It sure does stir up the soil." "Won't it spoil your hill?" asked Alice. "Not so's you could notice it. That hill isn't wuth much as it stands. It's too steep to plow, and only a goat could find a foothold on it to graze. So if you moving picture folks level it for me I may be able to raise some crops on it. Shoot as much as you like. You can't hurt that hill!" The men at the gun signaled that they were going to fire no more that day, and then, as it was safe, the young folks made a trip to see the extent of damage caused by the shells. Great furrows were torn in the earth and the stones, and the top of the hill, that had been rounding, was now quite flat, though far from being smooth.