Page:Popular Science Monthly Volume 91.djvu/56

This page needs to be proofread.


��Popular Science Monthly

��90 feet long. Heavy as the mass is, a huge lathe turns it around as easily as a body turns a spool. After the inside has been rifled or scored to form an inside surface that gives the shell a twist before it leaves the muzzle and causes it to fly straight, the lower or muzzle end of the gun is made larger. This may be accomplished in one of two ways. Either additional shorter steel tubes are placed over the main inner tube, or the main tube is wound with wire and finished with an outer tube. The wire-wound guns are usually the heavier and are used on board ship.

Why the Wire-Wound Gun Is So Strong

The gun bound with wire is really stronger than the one built of bands or rings of steel, one on another; for the wire reinforces the gun tube so that it will safely with- stand the tremendous strain which is constantly put on it when it is fired — said to be as much as seven- teen tons pressure on each square inch. This means a pressure on every little space inside the gun as big as a domino of over 38,000 pounds. No wonder that a gun

���The upper portion of a blast furnace in which pig iron is made — the first step in making steel. These men are dumping iron ore, coke and limestone into the large hopper. The materials are allowed to fall at intervals into the inside of the furnace where the intense blasts of hot air cause them to melt, mix and fuse together until they are tapped out at the bottom

���This is a steel ingot. It is the large block of steel resulting from pouring the hot liquid steel into a large mold and allowing it to cool. After it is cold the ingot is taken, in the manner here shown, to the large forge shop for conversion into a big gun. This block weighs something over 111 tons

�� �