Not only does this smokeless powder, burning inside these guns, produce enormous pressure, but it generates inconceivably great heat. Water boils at 100° Centigrade; iron melts at 1400°; platinum and the most resistant metals at 2900°; while the hottest thing on earth is the temperature of the electric arc, in which carbon boils. This temperature is between 3000° and 4000° Centigrade, and is believed to be the same as that of these great powder chambers when the gun is fired. Thus a diamond, the hardest substance known, would melt in the barrel of a twelve-inch gun at the moment of discharge. The consequence is that at each discharge of a big gun a thin skin of metal inside the barrel is literally fused, and this leads to rapid erosion of the softened surfaces under the tearing pressure of gases generated. The rifling is worn away; the band over the projectile becomes loose-fitting; and soon the huge gun, that has cost such a great sum, is rendered unfit for service. The life of a twelve-inch gun is only 450 rounds, that is, the gun would be worn out if fired every three minutes for a single day. After that a new life may be given it by boring out the inner tube and putting in a new steel lining. A Secret for Which Foreign Governments Would Pay Millions. A few words may be added about the formidable smokeless powder used in these great guns. This powder, in spite of its terrible power, is of innocent appearance, and a small stick of it may be held safely in the hand while it burns with a vivid yellowish flame. There is no danger of its exploding or detonating like gun-cotton, and yet it is made from gun-cotton, treated by a colloiding process that is one of our jealously guarded military secrets. There are foreign governments that would give millions to know exactly how this powder is made and how it is preserved for years without deterioration. The recent destruction of two ships of the French navy was due, it is believed, to deterioration of their smokeless powder. [Illustration] Why Do Some Eyes In a Picture Seem to Follow Us? If a person’s picture is taken with the eyes of the person looking directly into the lens or opening of the camera, then the eyes in the picture will always be directly on and appear to follow whoever is looking at it. This is also true of paintings. If a subject being painted is posed so as to look directly at the painter, and the artist paints the picture with the eyes so pointed, then the eyes of the picture will follow you. When you are looking at a picture of a person and the eyes do not follow you, you will know at once that he was not looking at the camera or artist when the picture was being taken or painted. [Illustration] Where Does a Light Go When It Goes Out? ~WHY YOU CAN BLOW OUT A CANDLE~