142 OUR PHYSICAL WORLD 



Finally, however, a device was found to overcome this. The 

 gun barrel was grooved with spiral grooves. The base of the 

 bullet was hollowed out and a sharp-pointed metal or wooden 

 ping was set in the hollow so that the explosion of the powder 

 drove in this peg, expanding the base of the bullet so the lead 

 was forced into the grooves, thus giving the bullet a twisting 

 motion about its long axis as it sped away from the gun, and it 

 would keep going straight. Moreover, this device made the 

 bullet fit the barrel tightly so no gases escaped around it as had 

 happened when the loosely fitting ball had been used. Now 

 there are added to the gun a magazine to hold a number of shells, 

 a shell ejector, and accurately gauged sights. 



The old muzzle-loading guns could not be fired very rapidly 

 for the loading process was slow and one must stand up to accom- 

 plish it. Loading at the breech was quicker, and it could be 

 done lying flat on the ground, so offering little target for an enemy 

 to shoot at. Added speed in firing was possible with the inven- 

 tion of the magazine gun. Several cartridges are carried in a 

 chamber in the stock. By the movement of a lever the empty 

 shell is ejected and a loaded one is brought up from the magazine 

 and slid into position ready to fire. In some rapid-fire machine 

 guns the force of the recoil is made to eject the old shell and bring 

 the next one into position. The shells are introduced in a long 

 belt, and the gun keeps up a continuous fusillade of shots, a 

 steady roar of discharge. 



When the bullet leaves the gun, gravity at once begins to pull 

 it down to earth at a rate of 16 feet the first second. The bullet 

 fired from the modern high-powered rifle has a velocity when it 

 leaves the muzzle of a half-mile a second. If the gun is aimed 

 at an object only 100 yards distant, the bullet is pulled down by 

 gravity only a few inches before it reaches its mark. But if the 

 object is a half-mile away, then the bullet must be fired several 

 feet above the object in order to hit it. The sights in the modern 

 gun can be set for various distances, and the muzzle is elevated 

 more and more for increasing distances. In recent tests of 



