Part 7

The men aboard the towing vessels that drag the floating targets during gun and mortar practice would seem to be in a dangerous position, since the tow-line is not more than two hundred yards long for guns and five hundred yards long for mortars, and a very slight error in aim or adjustment might cause a deviation of several hundred yards when the range is eight or ten thousand yards. As a matter of fact, such errors do not occur, and a gun-pointer who would make a right or left deviation from the target of ten yards, or at the most fifteen yards at a distance of five miles, would be considered unfit for his job. In one or two rare instances a towing vessel has been struck when a projectile has fallen short and then ricochetted to the right, as it invariably does owing to its rotation in that direction. The rifling of the gun-barrel causes this rotation.

Sometimes these great projectiles ricochet several times, and go bounding over the water as a pebble skips along the surface of a mill-pond, only there may be the distance of a mile or more between these giant leaps.

The Projectile Travels Faster Than the Sound It Makes.

A strange phenomenon is witnessed by the observer on a towing vessel as he looks, rather uneasily perhaps, toward the distant shore battery, that seems to be firing straight at him. First there is a flash and a puff of smoke; then nothing for a period of seconds, while the projectile is on its way; then suddenly a great splash as the mass of iron strikes the water. Up to this moment there has been no sound of the discharge, no sound of the projectile, since it travels faster than the sound-waves; but now, after it has buried itself in the ocean, is heard its own unmistakable voice, a low, buzzing um-m-m-m approaching from the shore. The projectile itself has arrived before the sound that it makes in transit, and the sound arrives afterward. Last of all is heard the boom of the discharge.

In this beautiful picture the hurling projectile was itself the photographer: that is, in passing out of the gun-barrel, it broke a length of piano-wire stretched across the muzzle and thus automatically closed an electrical circuit that actuated the camera mechanism. And so rapid was the shutter that the great shot hurled forth in the discharge photographed here has not yet had time to issue from the smoke-cone, where it is still hidden.]

Owing to the great velocity of gun projectiles, it is almost impossible for an observer near the target to see them as they approach; but a trained eye can discern the slower moving mortar projectiles as they drop out of the sky, shrieking as they come, curving downward from a height of four or five miles, half a ton falling from a height of four or five miles.

This photograph illustrates another important form of coast defense--the submarine mine. A target about 5 by 5 feet, with a red flag at its apex, is towed across the mine-field, the mines being exploded electrically from a shore station several miles away. The methods of laying and exploding these mines are carefully kept secrets. In this case a charge of five hundred pounds of the newest explosive was used. Fragments of the shattered target and mine-buoy are seen at the right of the picture. Tons of water are hurled into the air by these explosions, and hundreds of fish are killed or stunned.]

It is difficult to realize what an enormous force is released when one of these twelve-inch guns is discharged. The pressure inside of the gun behind the projectile is between thirty-five and forty thousand pounds to the square inch. No engine or machine made by man produces anything like this pressure. The boiler pressure in steam-engines, or in big turbines driven by superheated steam, does not exceed two hundred or three hundred pounds to the square inch. The huge hydraulic presses that would crumple up a steel girder do not exert a pressure of more than one thousand pounds to the square inch. The only reason a gun-barrel can resist this pressure (forty thousand pounds to the square inch) is that it is built up in a series of concentric steel hoops or tubes shrunk one over the other until there is a resistance capacity of from seventy thousand to ninety thousand pounds to the square inch. Even at rest, the barrels of these great guns are under such enormous compression, from being thus squeezed within these outer steel coverings, that, if the retaining steel jackets were suddenly cut, the tubes would blow themselves into pieces from the violent reaction of release.

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.

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.

Where Does a Light Go When It Goes Out?

~WHY YOU CAN BLOW OUT A CANDLE~

To understand the answer to this question fully you will first have to learn what light is, and particularly that it is not the flame from the gas jet or of the lamp or candle that is actually the light, but that light consists of rays or waves in the ether, which is constantly in all space and even in our bodies, coming from the something that is burning. This in the instance above mentioned would be the gas burning as it comes out of the gas jet, the oil in the lamp as it comes up through the wick or the flame of the candle. We are apt to call a lighted gas jet a lamp, or a candle, light, because it is steady. Really, however, there is no such thing as keeping light in a room in an actual sense, for rays of light travel from the substance which produces them faster than anything else we know of in the world. The first thing a light wave does when it is once created is to go some place, and it does this at the rate of 186,000 miles per second. If it cannot penetrate the walls of the room it is either reflected back in the direction from which it came or transformed by the objects which it strikes into some other kind of energy.

When you look at the rays coming from a gas jet, you do not see one ray for more than, say the millionth part of a second, but because these rays of light come so fast one after the other from the burning jet and spread in all directions, they seem to be continuous.

So you see that the rays of light are going away as fast as they are coming from the gas jet. They either go on as light or, as said above, are changed into other forms of energy when they strike things they cannot penetrate in the form of light, or rather one thing, which is heat. A large part of it goes into the air in the room in the form of heat, as you well know, now that it is called to your attention. Some of it goes into the furniture and some of it is changed into another form of heat, which, combining with the chemicals in other things it mixes with, changes their appearance and usefulness. As, for instance, the carpets and hangings in the room, the colors of which become faded when exposed to light rays too much. The heat from the light rays is responsible for the fading of colors in our garments as well.

When you “put out the light,” as we say, or turn off the gas, you cut off the source of light. Really, then, our expression that “the light goes out” is only true while the gas is lighted, for from the flaming gas jet the light is going out all the time, whereas when the gas is turned off no light is being produced, and when you turn off the gas you do not turn out the light, but only that which makes light.

Why Does a Fire Go Out?

Fire will go out naturally when there is nothing left to burn, or it will go out if it cannot secure enough oxygen out of the air to keep it going. In the first case it dies what we might call a “natural death,” and in the latter case the fire practically suffocates. The fire in the open fireplace, if it has plenty of air, will burn up everything burnable that it can reach. The stones of the fireplace or other parts of a stove will not burn, because they have already been burned, and you cannot burn anything a second time, if all of the oxygen in it was burned out of it the first time.

Now, then, to burn up a thing, you must first start a fire under it, and then keep a constant draft of air playing on it from beneath, or the fire will die out. The more difficult a thing is to burn, the more important it is that you have plenty of draft. If the ashes accumulate under the fire the air cannot go through them in sufficient quantity and the fire will go out. Other things which prevent the current of air from going up through the fire will cause it to go out. That is why we close the lower door of the furnace, to keep the fire from burning out. When we shut off the draft of air from below, the fire in the furnace burns slowly, i. e., it just hangs on, so to speak.

Why Does a Lamp Give a Better Light With the Chimney On?

When a lamp is burning without a chimney it generally smokes. That is because the oil which is coming up through the wick is being only partially burned. The carbon, which is about one-half of what the oil contains, is not being burned at all, and goes off into the air in little black specks with the gases which are thrown off. The reason the carbon is not burned when the chimney is off is that there is not sufficient oxygen from the air combining with it, as it is separated from the oil in the partial combustion that is going on. To make the carbon in the oil burn you must mix it with plenty of oxygen at a certain temperature, and this can only be done by forcing sufficient oxygen through the flame to bring the heat of the flame to the point where the carbon will combine with it and burn. When you put the chimney on the lamp you create a draft which forces more oxygen through the flame, brings the heat up to the proper temperature and enables the carbon to combine with it and burn. When you take the chimney off again the heat goes down, when the draft is shut off and the lamp smokes again.

The chimney also protects the flame of the lamp from drafts from the sides and above, and helps to make a brighter light, because a steady light is brighter than a flickering one.

The draft created by the chimney also forces the gases produced by the burning oil up and away from the flame. Some of these gases have a tendency to put out a light or a fire.

Does Light Weigh Anything?

To get at the answer to this question we must go back to the definition of light. Light is a wave in the ether and contains no particles of matter. It, therefore, does not weigh anything at all.