introduction of water, either into the blood, the stomach or the large

intestine, without having touched either the tongue or throat, which proves that it is not our tongue or throat that is thirsty, but the body itself. What Is Pain and Why Does It Hurt? Pain is the result of an injury to some part of our bodies, or a disturbed condition--a change from the normal condition. Pain is caused by nerves in the body. The network of nerves coming in big nerves from the back bone or spinal chord branches out in all directions, and near the surface of the skin they spread out like the tiny twigs of a tree, covering every point of the body. Some parts of our bodies are more sensitive than others. That is because the nerves are then nearer the surface or else there are more nerves in that part. The heel is perhaps the least sensitive part of the body, as the nerves do not lie so near the surface there. Pain is not a thing which you can make a picture of or describe in words. Pain is a sensation of the brain caused by a disturbance of conditions in some part of the body. If you cut your finger, you cut certain veins or arteries and also the tiny nerves in the finger. The nerves immediately let the brain know that they are injured, and the brain sets to work to have the damage repaired. But there is a congestion right where the cut is. The veins being cut, the blood which would ordinarily flow through them back to the heart, pours out into the cut and the inside of your finger is thus exposed to the oxygen of the air, and the action of the air on the exposed part helps to make the pain. It is not your finger, however, that hurts. It is the shock that your brain gets when you cut your finger that hurts. A pain in your stomach is a pain caused by something else than a cut. If the stomach could always digest everything or any amount of stuff you put in it, you would not have a stomach pain. But sometimes you put things into your stomach through your mouth, of course, that the stomach cannot handle. Or, it may be a combination of a number of things that cause this unusual condition in your stomach. The stomach makes a special effort to get rid of this troublesome substance and generally succeeds eventually, but while the fight is going on, it pains or hurts you. Pain is the result of a disturbance of the nerves. It is just the opposite of gladness. We sometimes are so glad we feel good all over. Pain is just the opposite. You can prove that pain is not a real thing but only a sensation. Perhaps you have had toothache. You go to the dentist and he kills the nerve or takes it out. After that you cannot have the toothache in that tooth again, because there is no nerve there to telegraph to the brain, even though the cause of the hurt still exists. You cannot feel pain unless the brain knows about the injury. What Is the Horizon? Of course you know what the horizon is. It is easiest to see the horizon at sea when out of sight of land. There, when you look in any direction from the ship to the place where the sea and the sky meet you see a line which, if you follow with your eye as you turn completely around, makes a perfect circle. It looks as though it marked the boundary of the earth. On land it is not easy to see as much of the horizon at one time, because of buildings and trees and hills in the woods and elsewhere, but if the land were perfectly smooth like the sea and there were no trees or buildings or hills in the way, you could see just as perfect a circle on land as on sea. This proves that the horizon is a movable circle. On land it is where the earth and sky appear to meet, and on water it is where sky and water appear to meet. How Far Away Is the Horizon? The actual distance of the horizon away from us depends altogether upon the height above the sea level from which we are looking as far as we can. The horizon is always as far away as we can see. At the seashore, where we are practically on a level with the water, we cannot see so far as when we are up on a bluff or hill overlooking the sea. The higher we go up straight from a given point the greater the distance we can see up to a certain point and the farther away the horizon will appear. The height of the person looking, of course, figures in this, because when you are at sea level it is only your feet really that are at sea level (if you are standing up straight) and the distance of the horizon is measured from the eye of the person looking. A boy or girl of ten would be, say, a little over four feet high, and the eyes of such a person would be about four feet above the level of the sea. At that height the horizon would be about two and a half miles away. If the eyes are six feet above sea level the distance of the horizon will be about three miles, so that practically every one sees a different horizon, that is, one that appears at a different distance. A hundred feet above the level of the sea the horizon will be more than thirteen miles away, while at 1000 feet altitude it would be 42 miles away, and if you could go a mile into the air the horizon would appear 96 miles from where you are. The higher you go the farther away the circle which apparently marks the joining of the earth and sky appears. Why Can We See Farther When We Are Up High? Remember that the earth is round and you will probably be able to answer the question yourself. This one, like most questions boys and girls ask, only requires a little thought. The earth, of course, as we have learned long ago, is a globe. When you look out on the land or the sea from a high place you can see more of the earth’s round surface before the curve of the earth’s surface takes things beyond the range of vision. If you are on a bluff 100 feet high at the seashore and looking toward a point where a ship is coming toward shore, you will be able to see the ship much sooner than if you were at the sea level. In exact words, you actually see more of the earth’s surface the higher up you are, because, as you go up your position in relation to the curvature of the earth’s surface changes. What Makes Lobsters Turn Red? When a lobster is taken out of the lobster trap with which the fisherman traps him, he is green, but when he comes to the table as a choice morsel of food his shell is red. We know that he has been boiled and we know that he goes into the boiling water green and comes out red. This change in the color of the shell of the lobster is the result of the effect of boiling water on the coloring material in the shell. When the lobster is put in the boiling water the process of boiling produces a chemical change in the color material in the lobster’s shell. There is no particular reason why the lobster should turn red, excepting that that is the effect boiling water has on the coloring matter in the shell. Why Do We Have to Die? Death must come to all things that have life. All matter in the world is either living (animate) or dead (inanimate). Inanimate things do not change. They remain always the same. We can change the form and size of inanimate things, and particles of them even help to make up the bodies of the living things, but what they are made of always remains what it was. Death is one of the things that must occur if we are to continue to have more life. The whole plan of living things includes the ability to reproduce themselves. Every kind of life has the power to produce life like itself and this process of reproduction is continuous. If there were no death, then the world would soon be crowded with living things to the point where there would be neither room nor food. [Illustration: WHERE WINDOW GLASS COMES FROM] Pictures herewith by courtesy of Pittsburgh Plate Glass Co. Making Plate Glass What Is the Difference Between Plate Glass and Window Glass? How is plate glass made? These questions are asked very frequently. The two products are wholly unlike each other; and we wish to show wherein lies the difference. We shall tell how plate glass is made; and we hope to make it clear that great care, time and expense are involved in its manufacture. The raw materials may be said to be virtually the same in plate glass as in window glass; the main difference being that in plate glass greater care is exercised in selecting and purifying the ingredients. Window glass is made with a blow-pipe. The work requires skill on the part of the operator; but the process is quite simple and rapid. And the result is, naturally, a comparatively ordinary and indifferent product. On the other hand, the superb quality of plate glass is owing to the elaborate method of producing it. Commercial plate glass was first made in France somewhat more than two hundred years ago; although glass in one form or another has been in use for many centuries. Apparently glass was known in Egypt fully four thousand years ago. [Illustration: MINING SILICA] The materials used are silica (white sand), carbonate of soda (soda ash), and lime. Other materials, as arsenic and charcoal, are used in small proportions, but the main ingredients are the first three named. Probably it is little imagined that in the production of plate glass, mining is involved in two or more forms (namely silica and coal), also the quarrying of limestone, the chemical manufacture of soda ash on a large scale, the reduction and treatment of fire clay to its right consistency, an elaborate and expensive system of pot making; and the melting, casting, rolling, annealing, grinding and polishing of the glass. In special uses, as in beveled plates and mirrors, two more elaborate processes must be added--beveling and silvering--all of which are performed under the direction of experts aided by a large amount of labor and expensive machinery. Pots of fire clay take so important a part in the successful manufacture of plate glass that the subject deserves especial notice. The different clays after being mined are exposed to the weather for some time to bring about disintegration. ~THE CLAY MUST BE TRAMPLED WITH BARE FEET~ At the proper stage finely sifted raw clay is mixed with coarse, burned clay and water. This reduces liability of shrinkage and cracking. It is then “pugged,” or kneaded in a mill; kept a long time (sometimes a year) in storage bins to ripen; and afterwards goes through the laborious process of “treading.” Nothing has thus far been found in machinery by which the right kind of plasticity can be developed as does this primitive treading by the bare feet of men. The clay must be treaded, not once or twice, but many times. The building of pots is a slow, tedious and time-killing affair; but this is most essential. ~HOW MELTING POTS ARE MADE~ Without extreme care, some elements used in the making of the pots might be fused into glass while undergoing the intense heat of the furnace; or they might break in the handling. The average pot must hold about a ton of molten glass, and the average furnace heat necessary is about 3,000° Fahrenheit. The work is not continuous. Each workman has several pots in hand at a time, and passes from one to another adding only a few inches a day to each pot, so that a proper interval for seasoning be given. After completion, comes the proper drying out of the pots; and this is another feature in which the greatest scientific care is required. No pot may be used until it has been left to season for at least three months, and even a year is desirable. And after all this trouble, the pot has but 25 days of usefulness. The pots form one of the heavy items of expense in plate glass manufacture; and upon their safety great things depend. [Illustration: POT MAKING.] [Illustration: MIXING THE CLAY. TRAMPLING THE CLAY.] [Illustration: SKIMMING THE POT.] [Illustration: CASTING PLATE GLASS.] ~HOW THE HUGE PLATES OF GLASS ARE CAST~ The pot, having been first brought to the necessary high temperature, is filled heaping full with its mixed “batch” of ground silica, soda, lime, etc. Melting reduces the bulk so much that the pot is filled three times before it contains a sufficient charge of metal. When the proper molten stage is reached the pot is lifted out of the furnace by a crane; is first carefully skimmed to remove surface impurities, and then carried overhead by an electric tramway to the casting table. This is a large, massive, flat table of iron, having as an attachment a heavy iron roller which covers the full width, and arranged so as to roll the entire length of the table. The sides of the table are fitted with adjustable strips which permit the producing of plates of different thicknesses. The pasty, or half-fluid glass metal is now poured upon the table from the melting pot, and the roller quickly passes over it, leaving a layer of uniform thickness. The heavy roller is now moved out of the way, and then by means of a stowing tool the red hot plate is shoved into an annealing oven. All of these stages of the work have to be performed with remarkable speed, and by men of long training and experience. The plates remain for several days in the annealing oven, where the temperature is gradually reduced from an intense heat at first, until at the end of the required period it is no hotter than an ordinary room. [Illustration: PREPARING THE GRINDING TABLE.] When the plate is taken from the annealing oven it has a rough, opaque, almost undulating appearance on the surfaces. It is only the surface, however, for within it is as clear as crystal. First, it is submitted for careful inspection, so that bubbles or other defects may be marked for cutting out. It then goes to the cutter who takes off the rough edges and squares it into the right dimensions; and thence to the grinding room. [Illustration: HOW THE GLASS PLATES ARE GROUND GRINDING THE PLATES] The grinding table is a large flat revolving platform made of iron, twenty-five feet or more in diameter. The plate must be carried from the annealing oven to the grinding machines, and thence to the racks, by men skilled in the art. Twenty men are required to carry the larger plates of glass, ten on each side, using leather straps and stepping together in perfect time. The lock-step is absolutely essential to prevent accident. The grinding table is prepared by being flooded with plaster of Paris and water; then the glass is carefully lowered, and a number of men mount upon the plate and tramp it into place until it is set. After this, greater security is obtained by pegging with prepared wooden pins; and then the table is set in motion. The grinding is done by revolving runners. Sharp sand is fed upon the table, and a stream of water constantly flows over it. After the first cutting by the sand, emery is used in a similar manner. The plates are inspected after leaving the grinding room, and if any scratches or defects of any kind are found they are marked. Some of these can be rubbed down by hand. There are also, not infrequently, nicks and fractures found at this stage; and in such case the plate must again be cut and squared. Afterward comes the polishing, which is done on another special table. The polishing material is rouge, or iron peroxide, applied with water, and the rubbing is done by blocks of felt. Reciprocating machinery is so arranged that every part of the plate is brought underneath the rubbing surface. The grinding and polishing has taken away from the original plate half of its thickness, sometimes more. There is no saving of the material; it has all been washed away. When to this waste is added the fact that fully half of the original weight of lime and soda has been released by the heat of the furnace, escaping into the atmosphere in fumes and acids, one may begin to understand something of the cost of converting the rough materials of sand, limestone and soda into beautiful plate glass. ~HOW MIRRORS ARE MADE~ In preparing plate glass for mirrors great care must be exercised in the selection of the plates. This selection bears reference not only to surface defects, but to the quality in general; defects which cannot ordinarily be seen are magnified many fold after the glass has received a covering of silver. [Illustration: BEVELING PLATES] In the process of beveling, the plate passes through the hands of skilled workmen of five different divisions, namely: roughers, emeriers, smoothers, white-wheelers and buffers; and different abrasive materials are used in the order indicated by the titles. These materials are sand, emery, natural sandstone imported from England, pumice and rouge. The roughing mill is a circular cast-iron disk about 28 inches in diameter, constructed so that the face or top of the mill revolves upon a horizontal plane at a speed of about 250 revolutions per minute. The sand is conveyed to the mill from above through a hopper simultaneously with a stream of water which is played upon the sand to carry it to the mill. The rougher places the edge of the plate upon the rapidly revolving mill, and the cutting of the bevel is done by the passage of the sand between the mill and the plate of glass. A bevel of any desired width may be produced. Pattern plates containing incurves, mitres, etc., require a practiced eye and great skill upon the part of the operator. When the plate leaves the rougher’s hands the surface of the bevel has been ground so deep by the coarse sand that polishing at this stage is impossible. Consequently, in order to produce a surface fine enough to render it susceptible of a high and brilliant polish it must go through the various treatments we have mentioned. The emerier uses a fine grade of emery on a mill similar in construction to a roughing mill, which takes away considerable of the coarse surface given by the first cutting. Then it goes to the smoother, who reduces the roughness slowly by using a fine sandstone from England; then it goes to the white-wheeler who operates an upright poplar-wood wheel using powdered pumice stone as an abrasive; and then, as a last stage it reaches the buffer, whose method of operation is shown in the illustration. The buffer brings a high polish to the bevel by the use of rouge applied to thick felt which covers his wheel. [Illustration: SILVERING MIRROR PLATES.] [Illustration: The two photographs here are of the same building taken under contrasting conditions. The first picture was taken through a window glazed with common window glass. It is an extreme example, to be sure, but of a sort not infrequently seen. The second view shows the same building taken through a window of polished, flawless plate glass. An observing person can see this startling contrast any day as he walks along a residence street. At intervals a front window will be seen which gives a twisted, distorted reflection of the houses or trees on the opposite side: this is window glass. The other kind--the window that gives a sharp brilliant reflection--is _plate glass_. It is practically impossible to obtain superior reflecting quality from window glass. It can only be had from surfaces which have been ground and polished.] The plate, after leaving the beveling room, is again carefully examined for surface defects. These defects may consist of scratches caused inadvertently by permitting the surface of the plate to come into contact with the abrasive material. These scratches are removed by hand polishing, which must be skillfully done; otherwise the reflection will become distorted through over-polishing in a given area or spot. The plate is then taken to a wash table where the surface to be silvered is thoroughly washed with distilled water; after which it is taken to a table that is covered with blankets, and which is heated to a temperature of from 90° to 110°. The blanketing is to protect the plate from being scratched, and also to catch all of the silver waste. The silvering solution is nitrate of silver liquefied by a certain formula, and is poured over the plate; the fluid having an appearance which to the ordinary observer looks like nothing other than pure distilled water. Within a few minutes the silver, aided by a reactory, added prior to pouring, begins to precipitate upon the glass; the liquids remaining above, and thus preventing air and impurities from coming into contact with the silver. Such contact would produce oxidation. After the silver is precipitated the plate is thoroughly dried, shellacked and painted; after which it is ready for commercial use. Until about 25 years ago, practically all mirrors were silvered with mercury. There have been two reasons for discouraging the use of mercury for silvering; one being its injuriousness to the health of the workmen. In some European countries stringent laws were enacted, stipulating that men should work only a certain number of hours. Other hygienic stipulations, added to the fact that the use of mercury was already very expensive, have tended to replace that process by the use of nitrate of silver. Why Is the Sky Blue? This question puzzled every one who thought of it for a long time. Even astronomers, the men who make a business of studying the skies, and other learned men, puzzled their brains about it and searched for the answer long ago, until finally, as always happens when a lot of people study a subject, Professor John Tyndall, a noted scientist of the last century, discovered the answer. The explanation follows: All the light we have is sunlight, which is pure white light. This white light is made up of rays of light of different colors. These rays are red, orange, yellow, green, blue, indigo and violet. It takes all of these different rays of light to make our white sunlight, and when you separate sunlight into its original rays you always produce the rays of light in the above colors and in the same order. This is only true, however, when the sunlight is passed through an object which does not absorb any of its rays. This is the arrangement of the different colors of light found in the rainbow. The rainbow is formed by sunlight passing into raindrops or vapor in such a way as to divide the sunlight into the different colored rays of light. When the rainbow is formed none of the rays are absorbed by raindrops or vapor through which the sunlight passes. Some of these rays of light are known as short rays and others as long rays. But when sunlight meets other things besides those which make a pure rainbow, these other objects have the ability to absorb some of the rays of colored light, and they throw off the remainder. When these rays have been thrown off those which have been absorbed make many different combinations, and thus are produced all of the different colors we know, the various tints and shades of color, according to composition and size. Now, then, to get back to the color of the sky, which is blue as we know. The sky or air which surrounds the earth is filled with countless tiny specks of what we may call dust--particles of solid things hanging or floating in the air. These specks are of just the size and quality that they catch and absorb part of the rays of light which form our sunlight and throw off the rest of the rays, and the part which has been absorbed forms the combination of color which makes our sky so beautifully blue. Sometimes you notice, of course, that the sky is a lighter or darker blue than at other times. This difference is due to the kind and condition of tiny specks in the air at the time, and to the direction or angle at which the sunlight strikes these tiny particles. This fact brings up a question which you have not asked, but which would come naturally as the result of your first. What Makes the Colors of the Sunset? The direction of the sun’s rays when they meet these large and small particles in the air has a great deal to do with the combination of colors that result as these objects absorb part of the rays and throw off others. The sky is the most beautiful blue when the sun is high in the sky. But when the sun is setting the light has a greater distance to travel through the belt of air which surrounds the earth than when it is high up over our heads. You know that if you stick a pin straight down into an orange it won’t go in very far before it is clear through the peel, but if you stick the pin into an orange along the edge it will go through a great deal more of the peel than the other way. That is the way it is with the sunset colors. The peel of the orange is a good representation of the belt of air which surrounds the earth. At sunset the light instead of coming straight down through the belt of air, thus meeting the eye through the shortest possible amount of air, strikes the air on a slant, and, therefore, travels through a great deal more air and closer to the earth to reach it, with the results that it meets a great many more of these little specks, besides all the smoke and other things that hang in the air near the ground, and we thus get many more colors, because some of the things in the air absorb some of the rays and others absorb very different rays when the light comes in this slanting way, and that is what makes the different colors in the sunset. For this reason sunsets are often richer and more beautiful in color when the air is not so pure, but has much dirt and other matter floating about in it. Are There Two Sides to the Rainbow? No, there is only one side to the rainbow. The rainbow is made by reflection of the rays of sunlight through drops of water in the air, but you can never see a rainbow unless you are between it and the sun. You could never see a rainbow if you were looking at the sun, and so if you are looking at a rainbow you can be certain that anyone on the other side of it could not see it, because they would have to be looking right at the sun. The rainbow is always opposite to the sun and there can never be two sides to it. Do the Ends of the Rainbow Rest on Land? The ends of the rainbow do not rest on anything. You see, the rainbow is only the reflection of the sun’s rays thrown back to us by the inside of the back of the raindrops, which are still in the sky after the rain. Of course, if any of the drops of water touched the ground they would cease to be raindrops and, therefore, could not reflect the rays of the sunlight. So, what we think of as the ends of the rainbow do not really exist at all. The rainbow is only a reflection of the rays of sunlight from countless drops of water in the air, which the sun’s rays must strike at a certain angle in order to reflect back the light so we can see it. Where the sun’s rays do not strike the drops of water at the right angle no light is reflected, and there is the end of the rainbow. What Causes the Different Colors of the Rainbow? The colors of the rainbow, which are always the same, and are shown in this order--red, orange, yellow, green, blue and violet--are sunlight broken up into its original colors. It takes all of these colors in the proportions in which they are mixed in the rainbow to make the pure sunlight. These are known as the prismatic colors. As shown in another answer to one of your puzzling questions, the rainbow is caused by the rays of the sun passing into drops of water in the air and reflected back to us with one part of the drop of water acting on it in such a way as to break up the pure sunlight into these prismatic colors. When a rainbow appears at a time when there is a great deal of sunlight, you will generally see two rainbows. The inner rainbow is formed by the rays of the sun that enter the upper part of the falling raindrops, and the outer rainbow is formed by the rays that enter the under part of the raindrops. In the inner or primary bow, as it is called, the colors beginning at the outside ring of color are red, orange, yellow, green, blue and violet, and being exactly reversed in the outer or secondary bow. The secondary bow is also fainter. You may sometimes see smaller rainbows, even if it has not been raining, when looking at a fountain or waterfall. These are caused in exactly the same way. What Makes the Hills Look Blue Sometimes? This is due to the fact that when the hills look blue you are looking at them at a distance, and there is a long stretch of air between you and the hills. This air is filled with countless particles of dust and other things, and what you see is not really blue hills, but the reflection of the sun’s rays from the little particles in the air striking your eye. The color is due to the angle at which the light from the sun strikes these particles, and is reflected back to your eye and partially due to the character of the particles in the air. Do the Stars Really Shoot Down? The answer is “No.” We have come to use the expression “shooting stars” commonly, but we should probably be more correct if we said “shooting rocks,” for the things we refer to commonly as “shooting stars” are more like rocks than anything else. If any of the real stars were to fall into the air surrounding the earth we should all be burned up by the great heat developed long before it actually hit the earth, which it would undoubtedly destroy. The things that fall and leave a streak of light are really only pebbles, stones, rocks or pieces of iron and other substances that fall from some place into the earth’s air belt. When they strike the air at the speed at which they are falling the friction of the air makes a heat that causes them to become luminous, and by far the greater part of them is burned up before they get very near the earth. We call them meteorites. Sometimes, though rarely, one will manage to strike the earth, coming at such great speed and being so large that the air has not been able to burn it up completely, and it will strike the earth and sink deep down into the soil. In most museums can be seen such meteorites that have been dug up after striking the earth. These are constantly falling into the air surrounding the earth, but in the day-time their light is not strong enough to be seen while the sun is shining. Will the Sky Ever Fall Down? No, the sky can never fall down, because it is not made of the kind of things that fall. We have become used to thinking of it as the roof of the earth, a great dome-shaped roof, because in our little way of looking at things we compared the earth and what is above it with the houses in which we live. The sky is just space in which the heavenly bodies revolve in their orbits. We cannot really ever see sky. We see only the sun’s light reflected by the air belt which surrounds the earth. In this air belt are the clouds which do come closer to the land at times than at others, and this is apt to aid in giving us an incorrect impression of this. What Is the Milky Way? The “Galaxy,” or “Milky Way,” as it is popularly called, is a luminous circle extending completely around the heavens. It is produced by myriads of stars, as can be seen when you look at it through a telescope. It divides into two great branches at one point, which travel for some distance separately and then reunite. It has also several branches. At one point it spreads out very widely into a fanlike shape. Why Do They Call It the Milky Way? The stars in the group are so numerous that they present to the naked eye a whiteness like a stream of milk. To produce this effect there are not hundreds of stars, nor thousands of them, but actually millions of them. When you stop to think that each one of these stars in the Milky Way is a sun like our own--some of them smaller, of course, but many of them much larger--you begin to realize how impossible it is for man to form any real idea of the magnitude and wonders of the earth. Here in the Milky Way are so many suns like our own sun that they together as we look at them form the particles of a path which makes the circle of the heavens, and yet are so far away that to the naked eye each of them looks to us like only one of countless drops of milk in a very large stream of milk that goes around the whole sky. Why Don’t the Stars Shine in the Day-time? The stars do shine in the day-time. If you will go down into a deep well or the open shaft of a deep mine and look up at the sky, of which you can see a circular patch at the top of the well, you will be able to see the stars in the day-time. The moon also shines in the day-time, on some part of the earth. At certain times during the month you can notice that the moon rises before the sun sets, and sometimes in the morning you can still see the moon in the sky after the sun is up. Usually you cannot see either the moon or the stars in the day-time, because the light from the sun is so bright and strong that the light of the stars and moon are lost in the brightness of the sun’s rays. When the moon is visible before the sun sets or after the sun has risen it is because the light of the sun is not so bright and strong at the beginning or close of daylight. If you are fortunate enough some time to witness a total eclipse of the sun you will be able to see the stars in day-time without having to go down into a deep well or mine shaft. How Far Does Space Reach? Space surrounds all earths, planets, suns, and extends for an infinite distance beyond each of them in all directions. It is impossible to measure in terms of human knowledge how far space extends. It is one of the things beyond the comprehension of the human mind, and for that reason man can never know in miles or the number of millions of miles how far it extends. Man has been able to measure the distance from the earth of some of the stars, and some of the nearest of them are millions of miles from the earth. Most of them are hundreds and even thousands of million miles away, and when we stop to think that space extends at least as far on the other sides of the stars as it does on this side, and even beyond that, we can readily understand that it is not only impossible to measure space, but also impossible to give in words any conception of what its limits might be. There is one word--infinite--which we are forced to use in speaking of the extent of space. Infinite means “without end,” unbounded, and so man has come to use the word “infinite” in describing the extent of space, and that is as near as any one can describe it. What Does Horse Power Mean? The term “horse power” is used in describing the amount of power produced by an engine or motor. When man made the first engines he needed some term to use in describing the amount of power his engine could develop. Up to that time man had used the horse for turning the wheels of his machinery and the horse to him naturally represented the most powerful animal working for man. When engines came into use they replaced the horses because they were capable of developing many times the power of the horse. In finding an expression which would accurately convey to the mind of another the power of a particular engine, it was natural to say that this engine would do the work of five, ten or more horses, and as this described it accurately and in a way that was entirely clear, it became customary to describe the power of an engine as so many times the power of one horse. To-day we still cling to the term “horse power” in describing the strength of the engine, although the horse-power unit used to-day is greater than the power of an average horse. To speak of an engine of one horse power to-day means an engine that has the power to lift 30,000 pounds one foot in one minute. [Illustration: WHERE OUR COAL COMES FROM A COAL BREAKER. Coal is brought in mine cars from several mine shafts and slopes, dumped onto a conveyor that runs on the inclined framework shown at the right of the picture. At the top it is broken in rolls, sorted and sized as it slides through the different screens, pickers, etc., and is finally delivered into railroad cars.] The Story in a Lump of Coal How Did the Coal Get Into the Coal Mines? The heavy black mineral called coal, which we burn in our stoves and furnaces, and use to heat the boilers of our engines was formed from trees and plants of various sorts. Most of the coal was formed thousands of years ago at a time when the atmosphere that envelopes the earth contained a much larger proportion of carbonic acid gas than it does now, and the climate of all regions of the earth was much warmer than it now is. This period was known as the carboniferous age, that is, the coal-making age, and its atmospheric conditions, favored the growth of plants, so that the earth was covered with great forests, of trees, giant ferns, and other plants, many of which are no longer found on the earth. In the warm, moist, and carbon-laden atmosphere of that period the growth of all kinds of plants was rapid and luxuriant, and as fast as old trees fell and partially decayed, others grew up in their places. In this way, thick layers of vegetable matter were formed over the soil in which the plants grew. In many places, where these beds were formed, the surface of the earth became depressed and the water of the sea flowed over the beds of vegetable matter. Sediment of various kinds was deposited over the vegetable matter, and in the course of centuries the sediment was transformed into rock. After the formation of the covering of sediment, the decay of the vegetable matter was checked, but a slow change of another kind was brought about by the pressure of the sedimentary deposits and the heat to which the plant remains were subjected. The hydrogen and oxygen which constituted the greater part of the plant substance was driven off and the carbon left behind. This change took place very gradually, through periods so long that we can only guess at their duration, but we know that many beds of coal were formed from layers of vegetable matter that were covered up many thousand years ago. [Illustration: MINE WORKERS THAT NEVER SEE DAYLIGHT Underground stable constructed of concrete and iron, with natural rock roof to avoid danger of fire. Mules are only taken to surface when mines are idle.] The coal first formed and submitted longest to pressure is known as hard coal, or anthracite. It is pure black, or has a bluish metallic luster. Its specific gravity is 1.46; which is about the same as that of hard wood. Anthracite contains from 90 to 94 per cent. of carbon, the remainder being composed of hydrogen, oxygen, and ash. [Illustration: The Mules and their drivers.--An important part of the haulage system. Mules are kept in stables on surface at this mine and driven in every day through slope or drift.] Hard coal may be called the ideal fuel and is especially adapted to domestic heating purposes. It burns without smoke and produces great heat. There is no soot deposit upon the walls of chimneys, and in good stoves or furnaces the small amount of gas given off by it is consumed. Anthracite is the least abundant of all the varieties of coal and is much more costly than the other varieties. For this reason it is not much used in manufacturing. [Illustration: HOW THE SLATE PICKERS WORK Boy slate pickers. Coal slides down the chutes. Boys pick out the slate and rock and throw into chute alongside.] [Illustration: Spiral slate pickers do work of many boys. Coal and rock start together at the top in the small inner spiral. The coal being lighter slides faster, and in going around is carried over the edge into the outer spiral, while the rock continues in the bottom.] The coal formed later is very different in composition and is called bituminous or soft coal. Its name is derived from the fact that it contains a soft substance called bitumen, which oozes out of the coal when heat is applied to it. Soft coal contains from 75 to 85 per cent. of carbon, some traces of sulphur, and a larger percentage of oxygen and hydrogen than anthracite. When soft coal is heated in a closed vessel or retort, the hydrogen and oxygen, in combination with some carbon, are driven off. [Illustration: HOW A COAL MINE LOOKS INSIDE Shaft gate. One of the two cages in the shaft has just brought the men to the surface; the other is at the bottom. Safety gate resting on top of cage covers top of shaft when cage is down, as shown at right.] [Illustration: Section showing Anthracite Seams. Coal is shown black; rock and dirt lighter; shaft tunnels and workings, white. Upper part of “Mammoth” seam is stripped and quarried.] [Illustration: Lignite mine in Texas. Loaded mine cars ready to go to surface.] [Illustration: HOW THE MINERS LOOSEN THE COAL Undercutting with pick. The man lying on his side cuts under the coal. A light charge of powder exploded in a drill hole near the roof breaks the coal down in large pieces.] Soft coal is black, and upon smooth surfaces it is glossy. It lacks the bluish luster sometimes seen in hard coal and is much softer and more easily broken. When handled it blackens the hands more than hard coal does. In this kind of coal are frequently seen the outlines of leaves and stems of plants that enter into its formation. Occasionally, trunks of trees with roots extending down into the clay below the bed of coal have been found. [Illustration: Undercutting in seam. A compressed air driven machine undercuts deeper and faster than the man with a pick.] Soft coal has a specific gravity of 1.27. It burns with a yellow flame which is larger than the flame from hard coal, but it does not emit so high a degree of heat. Combustion, generally imperfect, gives rise to offensive gases and to black smoke that concentrates in the air and falls to the ground as soot, which blackens buildings, and, in winter, noticeably discolors the snow. The formation of lignite has been observed in the timbers of some old mines in Europe. In some of these mines wooden pillars have been supporting the rocks above for four hundred years or longer, and in that time the pressure of the rocks and other influences acting upon the wood of the pillars have caused it to become transformed into a brown substance resembling lignite. This fact tends to confirm the theory of coal formation stated at the beginning of this article. The proportion of carbon in lignite is never above 70 per cent., and the ash indicates the presence of considerable earthy matter. It is chiefly used in those forms of manufacture where a hot fire is not required. In Europe it is used, to some extent, in heating the houses of the poorer classes. Peat is regarded as the latest of the coal formations. In it, the change in the vegetable matter has not extended beyond merely covering it, and subjecting it to slight pressure. Peat is formed in marshy soils where there is a considerable growth of plants that are constantly undergoing partial decay and becoming covered by water. It consists of the roots and stems of the plants matted together and mingled with some earthy material. When freshly dug out of the bog or marsh in which it was formed there is always a quantity of water in it, the amount being greatest in the peat found nearest the surface and least in that at the bottom of the bed, where the peat is not very different in appearance from lignite. Peat is used for fuel where wood is scarce and coal is high in price. Recent experiments in saturating peat with petroleum, have shown that in this way a form of fuel may be produced for which considerable value is claimed. Its manufacture is confined to Southern Russia, where peat is plentiful and petroleum is cheap. Why Does Firedamp Explode in a Safety Lamp Without Producing an Explosion of the Gas With Which the Lamp Is Surrounded? The passing of the flame from the lamp to the outside air is prevented by the gauze. This splits the burning gas into little streamlets (784 to each square inch of gauze), which are cooled below the point of ignition, that is, are extinguished by coming in contact with the metal of the gauze, so that the flame does not pass outside the lamp. In some cases the explosion may be so great as to force the flame through the gauze and thus ignite the gas outside. Are There Any Conditions Under Which it Would Not Be Safe to Use a Safety Lamp? ~THE DANGERS TO THE MINERS~ The underground conditions affecting the safety of the lamp are exposure in air-currents of high velocity by reason of which the flame may be blown through or against the gauze, or exposure for too great a time to mixtures of air and gas which will burn within the lamp and thus heat the gauze. The dangerous velocity of air-currents begins at about 500 feet a minute, but varies with the type of lamp, some being much less sensitive to air-currents of high velocity than others. Other conditions under which the lamp is not safe concern the lamp itself or the one using it. The lamp is dangerous in the hands of inexperienced persons or when the gauze is dirty or broken. If the gauze is dirty, that portion absorbs the heat and may become hot enough to ignite the outside gas; naturally any holes in the gauze will pass the flame. The safety lamp when left too long in air containing much explosive gas may cause an explosion, and it is extinguished by certain unbreathable gases. The electric lamp burns safely regardless of the atmosphere, but gives no warning of poisonous or explosive gases. It is often used by rescue men wearing oxygen helmets to enter mines full of poisonous gases after explosions. [Illustration: THE LAMP WHICH SAVES MANY LIVES The safety lamp. The sheet iron bonnet or covering of the upper part protects the gauze within from strong currents of air, while the glass permits the light to be diffused. The above is a modern lamp similar to a bonnetted Clanny lamp.] The safety lamp is dangerous when there is a hole in the gauze that will permit the passage of flame to the outside, or when the gauze is dirty, so that any particular spot may be overheated, or when the velocity of the air is so great that the flame is blown through the gauze, or (generally) when in the hands of an inexperienced person. The unbonneted Davy lamp is not safe where the velocity of the air exceeds 360 feet per minute. The velocity with which the air strikes a lamp carried against it is increased by the amount equal to the rate at which the fireboss travels. If he walks at the rate of, say, 4 miles an hour or 352 feet a minute (on the gangways he will usually have to move faster than this to make his rounds on time) he will create by his own motion (and in still air) a velocity practically the same as that at which the unbonneted Davy is considered unsafe. [Illustration: Open oil lamp commonly worn on hat. Wick is inverted in spout.] [Illustration: Acetylene or carbide lamp for cap or hand.] History of the Safety Lamp. The safety lamp, the miner’s faithful and indispensable companion at his dangerous work, has been, heretofore, considered as the invention of the famous English scientist, Humphrey Davy, though the name of George Stephenson, of locomotive fame, has also been mentioned in this connection. Both came out with their inventions about the same time, but neither of them is the real inventor of the safety lamp; for there was, as proven by Wilhelm Nieman, a safety lamp in existence two years before Davy’s invention became known. It was not inferior to the latter, but rather surpassed it in illuminating power. Previous to this, all the precaution employed for the prevention of the threatening dangers of firedamp had been quite incomplete. One tried to thoroughly ventilate the mines by fastening a burning torch to a large pole, which was pushed ahead and exploded the gases. This was extremely dangerous work which, in the Middle Ages, was generally done by a criminal, in order that he might atone for his crimes, or by a penitent for the benefit of mankind. The attempt to substitute for the open light phosphorescent substances, encased in glass, was not much of a success. An improvement was the so-called steel mill, invented about 1750 by Carlyle Spedding, manager of a mine. This steel mill consisted of a steel wheel which was put into rapid motion by means of a crank. By pressing a firestone against the fast revolving wheel, an incessant shower of sparks was produced giving a fairly good and absolutely safe illumination. However, the running expenses of his apparatus, which necessitated the continual services of one man, were very high; for instance, the expenditure for light in a coal mine near Newcastle in the year 1816 amounted to about $200 per week. Nevertheless, the steel mill was very much appreciated and in use for a long time, only to be slowly supplanted by the safety lamp. [Illustration: ELECTRIC CAP LAMP AND BATTERY. The safety lamp when left too long in air containing much explosive gas may cause an explosion, and it is extinguished by certain unbreathable gases. The electric lamp burns safely regardless of the atmosphere, but gives no warning of poisonous or explosive gases. It is often used by rescue men wearing oxygen helmets to enter mines full of poisonous gases after explosions.] ~THE MAN WHO INVENTED THE SAFETY LAMP~ At the beginning of the nineteenth century the existing coal mines were worked to the limit and the catastrophies, caused by firedamp, increased in an alarming manner. In fact the distress was so great that in 1812 a society for the prevention of mine disasters was formed at Sutherland, and the origin of the safety lamp can be traced back to the efforts and labors of this organization. Dr. William Reid Clanny, a retired ship’s surgeon, was probably the first to undertake the task (in the year 1808), which he successfully finished with energy and skill. He concentrated his efforts at first on the separation of the flames from the surrounding atmosphere, but he did not succeed till the latter part of 1812, when he constructed a lamp that seemed to meet all requirements. The report of this invention was submitted to the Royal Society of London, May 20, 1813, and was printed in the minutes of that academy. The casing of this original safety lamp was closed at the top and bottom by two open water tanks; the air was pumped in by means of bellows and, passing in and out, had to go through both these reservoirs which acted as valves, so to speak. The lamp proved to be absolutely safe and was successfully introduced by the management of Herrington Mill pit mine. The clumsy parts of this apparatus were eliminated by its inventor by various improvements. The so-called steam safety lamp was completed in December, 1815, and installed in several mines. In the meanwhile, two competitors made their appearance. George Stephenson had finished his lamp October 21, 1815, and Davy published his first experiments November 9, 1815, in the Transactions of the Royal Society of London. Clanny’s lamp, nevertheless, stood the test in the face of this competition, through its much superior illuminating power, and more particularly as it still continued to burn when the Davy and Stephenson lamps had gone out. To Clanny, therefore, belongs the distinction, in the history of invention, of having constructed the first reliable safety lamp. What Is a Metal? The oldest known metals in the world are gold and silver, copper, iron, tin and lead. They are to-day still the most useful and widely-used metals. Some of the properties by which we distinguish metals are the following: They are solid and not transparent; they have luster and are heavy. Mercury is an exception to the rule; it is a liquid, though yet a metal, and there is another, sodium, which is solid, though very light. What Is the Most Valuable Metal? If you were guessing you would naturally say that gold is, of course, the most valuable of the metals. But you would be wrong. The proper answer to this is iron. We do not mean the pound for pound value, for you could get much more for a pound of gold than for a pound of iron. We mean in useful value--iron is in that sense the most valuable metal known to man. This is true because iron is of such great service to man in so many ways, and it is very fortunate that there is such a great amount of it available for man’s purposes. Iron is not generally found in a pure state in the mines. It is generally found compounded with carbon and other substances, and we obtain pure iron by burning these other substances out of the compound. Iron is put upon the market in three forms, which differ very much in their properties. First, there is cast-iron. Iron in this form is hard, easily fusible and quite brittle, as you will know if you ever broke a lid on the kitchen range. In the form of cast-iron it cannot be forged or welded. Next comes wrought-iron, which is quite soft, can be hammered out flat or drawn out in the form of a wire and can be welded, but fusible only at a high temperature. Third comes steel, the most wonderful thing we produce with iron. It is also malleable, which means that it is capable of being hammered out flat and can easily be welded, and this is the great property of steel--it acquires when tempered a very high degree of hardness, so that a sharp edge can be put on it, and when in that shape it will easily cut wrought-iron. Ordinarily we make wrought-iron and steel from iron that has been changed from its original state to cast-iron. The term cast-iron is generally given to iron which has been melted and cast in any form desired for use. Stoves are made in this way. The iron is melted and then poured into a mold; while the product out of which wrought-iron and steel are made is technically cast-iron, the term pig-iron is used in speaking of iron which is cast for this purpose. The process by which pig-iron is changed into wrought-iron is called _puddling_. The object of puddling, which is done in what is called a reverberatory furnace (which is a furnace that reflects or drives back the flame or heat) is to remove the carbon which is in the pig-iron. This is done partly by the action of the oxygen of the air at high temperature and partly by the action of the cinder formed by the burning furnace. When this has been done the iron is made into balls of a size convenient for handling. These are “shingled” by squeezing or hammering and passed between rolls by which the iron is made to assume any desired form. Now we come to steel, the most wonderful product or form in which we take advantage of the value of iron. Steel was formerly made from wrought-iron, so that you first had to get cast-iron, from which you made wrought-iron, and eventually got steel by changing the wrought-iron. Now we make steel direct from pig-iron. This is known as the Bessemer process. The most noticeable feature in the chemical composition of the different grades of iron and steel is found in the percentages of carbon they contain. Pig-iron contains the most carbon; steel the next lowest, and wrought-iron the least. Iron has been known to men from early historical times. The smelting of iron ores is not any indication of advanced civilization either. Savage tribes in many parts of the world practiced the art of smelting, even before they could have learned it from people who had become civilized. Why Is Gold Called Precious? Gold is called one of the precious metals because of its beautiful color, its luster, and the fact that it does not rust or tarnish when exposed to the air. It is the most ductile (can be stretched out into the thinnest wire), and is also the most malleable (can be hammered out into the thinnest sheet). It can be hammered into leaves so thin that light will pass through them. Pure gold is so soft that it cannot be used in that form in making gold coins or in making jewelry. Other substances, generally copper, are added to it to make the gold coins and jewelry hard. Sometimes silver is also added to the gold with copper. The gold coins of the United States are made of nine parts of gold to one of copper. The coins of France are the same, while the coins of England are made of eleven parts of gold to one of copper. The gold used for jewels and watch-cases varies from eight or nine to eighteen carats fine. Another reason why gold is called a precious metal is that it is very difficult to dissolve it. None of the acids alone will dissolve gold, and only two of them when mixed together will do so. These are nitric acid and hydrochloric acid. When these two acids are mixed and gold put into the mixture the gold will disappear. What Do We Mean By 18-Carat Fine? We often hear people in speaking of their watches say, “It is an 18-carat case.” Others speak of 14-carat watches or 22-carat or solid-gold rings. When you see the marks on a watch-case or the inside of a gold ring they read 18 K or 14 K, or whatever number of carats the maker wishes to indicate. A piece of gold jewelry marked 18 K or 18 carats means that it is three-fourths pure gold. In arranging this basis of marking things made of gold, absolutely pure gold is called 24 carats. Then if two, six or ten twenty-fourths of alloy has been added, the amount of the alloy is deducted from twenty-four, and the result is either 22, 18 or 14 carats fine, and so on. On ordinary articles made by jewelers the amount of pure gold used is seldom over 18 carats, or three-fourths. Weddings rings (and these are considered solid gold) are generally made 22 carats fine, that is, there are only two twenty-fourth parts of alloy in them. Why Does Silver Tarnish? Silver is a remarkably white metal, which is associated with gold as one of the precious metals. It is harder than gold and will not rust, although it will tarnish, which gold will not, when exposed to certain kinds of air. The silver tarnishes when it is exposed to any kind of air that has sulphur mixed in it. It ranks below gold as a precious metal for use in making ornaments and is not so costly, because there is a great deal more of it to be found in the world. While silver is somewhat harder than gold, it is still not sufficiently hard to use pure for making coins, so, as in the case of the gold coins, it is mixed with something else--copper--to harden it. Otherwise our dimes and quarters would wear out too rapidly. Our silver coins are made of nine parts of silver to one of copper. The coins of France are in the same proportion, while the silver coins of England are made of 92¹⁄₂ parts of silver to 7¹⁄₂ parts of copper. German silver coins are made of three parts of silver and one of copper. Why Do We Use Copper Telegraph Wires? One of the characteristics which distinguishes copper is its color--a peculiar red. It stands next to gold and silver in ductility and malleability, and comes next to iron and steel in tenacity--which means the ability of its tiny particles to hang on to each other. That is why copper wire bends instead of breaking when you twist it. But that is not the only reason, although an important part of the reason, why we use copper for telegraph wires. Copper is an extremely good conductor of electricity when it is pure. So are gold and silver, but we cannot afford to buy gold and silver wires for the telegraph, telephone and other wires, and if we used such wires the cost of the equipment would be so great that we could not afford to have telephones in our homes. But there is a great deal of copper in the world and it is very cheap, and so it makes an ideal element for use in things through which electricity is to pass. When you compound it with other substances it loses some of its conductivity. Copper is used extensively in many ways in the world. This book is printed, for instance, from copper electrotype plates. The whole business of electrotyping is based on the use of copper. Why Is Lead So Heavy? Lead is a white metal and is noted for its softness and durability. It has a luster when freshly cut, but becomes dull quite soon after the freshly-cut surface is exposed to the air. Lead is the softest metal in general use. It can be cut with an ordinary knife. It can be rolled out into thin sheets, but cannot be drawn out into wire. Lead is a very dense metal, that is, its particles are very compact and there is no room for air to circulate in between these particles. A piece of wood is lighter than a piece of lead of exactly equal bulk, because the little particles which make up the piece of wood are not very close together, and there is a lot of air in the ordinary piece of wood, while this is not true of the lead. A great deal of lead is used in making pipes for plumbing. This is because lead pipe is comparatively cheap, although you might not think so when you think of the general conclusions we have been brought to form about plumbers and everything connected with them. Lead pipe is easily bent in any direction also, and is particularly good for use in plumbing for that reason. Another wide use of lead is in making paints--white lead being the base used in making oil paints. The process of making white lead for paint is quite interesting and pictures of it are shown in “The Story In a Can of Paint” in another part of “The Book of Wonders.” Why Are Cooking Utensils Made of Tin? Tin is the least important of the six useful metals. It is also inferior in many ways to the others in this group of elements, but is tougher than lead and will make a better wire, though not a really good one. It has a whiteness and a luster that are not tarnished by ordinary temperature and is cheap. That is why it is used in making cooking utensils, pans, etc., and for roofs. But the pans, roofs, etc., are not pure tin. They are thin sheets of iron coated with tin. Pure tin would not be strong enough for these purposes, so a sheet of iron is first taken to supply the strength and then covered with tin to improve the appearance of the tin pans and keep them from rusting rapidly. What Is Gravitation? Gravitation is the result of the attraction which every body, no matter what its size, has for every other body. It is a strange force and difficult to explain in plain words. It is what keeps the heavenly bodies in their paths. Every one of the planets is held in its path by gravitation and every object on each of the planets is kept on the planet by gravitation. We can come nearer understanding gravitation by studying the effect of the attraction of gravitation on our own earth and the objects on it. When you throw a ball or a stone into the air it is the attraction of gravitation that causes it to come back. If this were not so the stone would go on up and up and would keep on going forever. If it were not for this wonderful force you could jump into the air and just keep on going up with nothing to bring you back. The reason you do not pull the earth toward you is because the body or mass with the greater bulk has always the greater pulling power. This is a wonderful force. It cannot be produced nor can it be destroyed or lessened. It just is. It acts between all pairs of bodies. If other bodies come between any pair of bodies the attraction of gravity between the two outside bodies is neither lessened or increased, and yet each of the outside bodies will have an independent attraction or pull on the body which is in between. No particle of time is spent by the transmission of the force of gravity from one body to another, no matter how far apart they may be. The only effect that distance has on the attraction of gravitation is to lessen its force. Any body which is being pulled through gravity toward another body would fall toward the center of the attracting body if all the force of attraction from all other bodies were removed. What Is Specific Gravity? Specific gravity is the ratio of weight of a given bulk of any substance to that of a standard substance. The substances taken as the standard for solids and liquids is water, and air or hydrogen for gases. Since the weights of different bodies are in proportion to their masses, it follows that the specific gravity of any body is the same as its density, and we now generally use the term “density” instead of specific gravity. To find, for instance, the specific gravity of a given bulk of silver, we must take an equal bulk of water and weigh it. Then we also weigh the silver. We find that the silver weighs ten and a half times as much as the water, and so the specific gravity of silver is 10.5. If you will bear in mind that water is the standard used for measuring the specific gravity of solids and liquids, and that air or hydrogen are used as standards for the gases, you will always know what the figures after the words specific gravity mean. Why Do We See Stars When Hit On the Eye? We do not really see stars, of course, when we are hit on the eye or when we fall in such a way as to bump the front of our heads. What we do see, or think we see, is light. To understand this we must go back to the explanation of the five senses--sight, hearing, feeling, tasting and touching. Now, each of these senses has a special set of nerves through which the sensations received by each of the senses is communicated to the brain and, as a rule, these special nerves receive no sensations excepting those which occur in their own particular field of usefulness. The eye then has nerves of vision; the nose, nerves of smell; the ear, nerves of hearing; the mouth, nerves of taste, and the entire body nerves of touch. As we have seen then, these special nerves are susceptible of receiving impressions or sensations only in their particular field. But, if you should be able to rouse the nerves of smell in an entirely artificial way and give them a sensation, they might easily act very much as though they smelled something. We find this often in the nerves of touch when we think we feel something when we do not. Now, when some one hits you in the eye, the nerves of vision are disturbed in such a way as to produce upon the brain the sensation of seeing light. In other words, you cannot affect the eye nerves without causing the sensation of light, and that is just what happens when some one hits you in the eye. [Illustration: “ARGONAUT, JUNIOR.” Experimental Boat, 1894.] [Illustration: “ARGONAUT THE FIRST.” Built 1896-1897.] The Story in a Submarine Boat How Can a Ship Sail Under Water? Up to a few years ago the stories we could tell about the ships that sail beneath the water were the creations of the minds of writers of fiction, like the author of “Twenty Thousand Leagues Under the Sea,” but to-day we can read of many actual trips beneath the water by the brave men who man our submarines. We never dreamed that the great story of Jules Verne would be realized in the little but very destructive ships of war which can be seen to-day in the naval ports of the nations of the world. We might have had these submarines long ago but for the fact that the men who were trying to invent them would not give up the secrets which they had discovered. Many men in different parts of the world worked on this problem and each discovered one or more things which were valuable in working out a solution, and if they had all gotten together and compared notes between them they could have produced a submarine boat almost as good as those we have to-day. How Does the Submarine Get Down Under the Surface? The first essential in a vessel to enable it to navigate below the surface of the water is that it be made sufficiently strong to withstand the surrounding pressure of water, which increases at the rate of .43 of a pound for each foot of submergence. A boat navigating at a depth of 100 feet would therefore have 43 pounds pressure per square inch of surface, or 6192 pounds for every square foot of surface. It will readily be seen, therefore, that the first essential is great strength. Therefore, the submarine boats are usually built circular in cross section with steel plating riveted to heavy framing, as that is the best form to resist external pressure. These boats are built for surface navigation as well, therefore they have a certain amount of buoyancy when navigating on the surface, the same as an ordinary surface vessel. When it is desired to submerge the vessel this buoyancy must be destroyed, so that the vessel will sink under the surface. Now, the submerged displacement of a submarine vessel is its total volume, and, theoretically, a vessel may be put in equilibrium with the water which it displaces by admitting water ballast into compartments contained within the hull of the vessel, therefore, if a vessel whose total displacement submerged was 100 tons, the vessel and contents must weigh also 100 tons. If it weighed one ounce more than 100 tons it would sink to the bottom. If it weighed one ounce less than 100 tons it would float on the surface with a buoyancy of one ounce. If it weighed exactly 100 tons it would be in what submarine designers specify as being “in perfect equilibrium.” It is possible to give a vessel a slight negative buoyancy to cause her to sink to, say, a depth of 50 feet and then pump out sufficient water to give her a perfect equilibrium, and thus cause her to remain at a fixed depth while at rest. In practice, however, this is seldom done. Most submarine boats navigate under the water with a positive buoyancy of from 200 to 1000 pounds and are either steered at the depth desired by a horizontal rudder placed in the stern of the vessel, or are held to the depth by hydroplanes, which hydroplanes correspond to the fins of a fish. They are flat, plane surfaces, extending out from either side of the vessel, and when the vessel has headway, if the forward ends of these planes are inclined downward, the resistance of the water acting upon the planes is sufficient to overcome the reserve of buoyancy and holds the vessel to the desired depth. If the vessel’s propeller is stopped, the boat, having positive buoyancy, will come to the surface. By manipulating either the stern rudders or the hydroplanes, the vessel may be readily caused to either come nearer to the surface or go to a greater depth, as the change of angle will give a greater or less downpull to overcome the reserve of buoyancy. The above description applies to navigating a vessel when between the surface of the water and the bottom. Another type of vessel which is used for searching the bottom in locating wrecks, obtaining pearls, sponges, or shellfish, is provided with wheels. In this type of vessel the boat is given a slight negative buoyancy, sufficient to keep it on the bottom, and it is then propelled over the water bed on wheels, the same as an automobile is propelled about the streets. This type of vessel is also provided with a diver’s compartment, which is a compartment with a door opening outward from the bottom. If the operators in the boat wish to inspect the bottom, they go into this compartment and turn compressed air into the compartment until the air pressure equals the water pressure outside of the boat; i. e., if they were submerged at a depth of 100 feet they would introduce an air pressure of 43 pounds per square inch into the diving compartment. The door could then be opened and no water could come into the compartment, as the diving compartment would be virtually a diving bell. Divers can then readily leave the boat by putting on a diving suit and stepping out upon the bottom. [Illustration: ONE OF THE FIRST PRACTICAL SUBMARINES “PROTECTOR.” BUILT 1901-1902, BRIDGEPORT, CONN. This was the pioneer Submarine Torpedo Boat of the level-keel type, and was built in Bridgeport in 1901-1902. It was shipped to St. Petersburg, Russia, during the Russian-Japanese war. From St. Petersburg it was shipped to Vladivostok, 6000 miles across Siberia, special cars being built for its transport.] [Illustration: This picture illustrates the same vessel, also at full speed under engines, with the conning-tower entirely awash and with the sighting-hood and the Omniscope alone above water. Notwithstanding the limited areas exposed above the surface, still observation could be had well-nigh continuously either through the dead-lights in the sighting-hood or by means of the Omniscope. In neither condition is it necessary to have recourse to electrical propulsion--the boats can still be safely and speedily driven as here shown under their engines.] [Illustration: THE INSIDE OF A SUBMARINE THE “G-1” RECENTLY DELIVERED TO THE UNITED STATES GOVERNMENT. The largest, fastest submarine in the United States and the most powerfully armed submarine torpedo boat in the world. In addition to the usual fixed torpedo tubes arranged in the bow of the vessel, which requires the vessel herself to be trained, the (seal) “G-1” carries four torpedo tubes on her deck which may be trained while the vessel is submerged, in the same manner as a deck gun on a surface vessel is trained, and thus fired to either broadside, which gives many technical advantages.] [Illustration: The above view gives a general idea of the interior of a submarine torpedo boat and the method of operation when running entirely submerged with periscope only above the surface. The commanding officer is at the periscope in the conning tower directing the course of the submarine through the periscope, which is a tube arranged with lenses and prisms which gives a view of the horizon and everything above the surface of the water, the same as if the observer in the submarine was himself above water. The steersman is shown just forward of the commanding officer and steers the vessel by compass under the direction of the commanding officer, the same as when navigating above the surface. In the larger type boats the steersman also has a periscope which enables him to see what is going on above the surface. Below decks two of the crew are shown loading a torpedo into the torpedo tube; each torpedo is charged with gun-cotton and will run under its own power over a mile and will explode on striking the enemy. The crew live in the compartment aft of the torpedo room. Aft of this is the engine room, in which are located powerful internal combustion engines for running on the surface and electric motors for running submerged. The electric motors are driven by storage batteries located under the living quarters. Wheels are shown housed in the keel, which may be lowered for navigating on the bottom in shallow water. A diving compartment in the bow permits divers to leave the vessel when on the bottom, to search for and cut or repair cables or to plant mines.] [Illustration: A SUBMARINE SAILING CLOSE TO THE SURFACE A submarine running partly submerged with the conning tower hatch open, showing the remarkable steadiness of this type of boat in a semi-submerged condition, a thing no other craft could safely accomplish.] [Illustration: Another submarine running entirely submerged, periscope only showing. The flag is attached to top of periscope to show her position in maneuvers when periscope goes entirely under water.] [Illustration: A PHOTOGRAPH TAKEN WITH THE PERISCOPE UNIVERSAL LENS.] AN ALL-SEEING EYE FOR THE SUBMARINE Vision under water is limited to but a few yards at best, and hence a submarine boat, when submerged, would be as blind as a ship in a dense fog and would have to grope its way along guided only by chart and compass, were it not for a device known as a periscope, that reaches upward and projects out of the water, enabling the steersman to view his surroundings from the surface. Of course the height of the periscope limits the depth at which the craft may be safely sailed. Nor can the periscope tube be extended indefinitely, because the submarine must be capable of diving under a vessel when occasion demands. But when operating just under the surface, where it can see without being seen, the craft is in far greater danger of collision than vessels on the surface, because it must depend upon its own alertness and agility to keep out of the way of other boats. The latter can hardly be expected to notice the inconspicuous periscope tube projecting from the water in time to turn their great bulks out of the danger course. The foregoing article describes the type of periscope now in common use on submarines and one of the engravings on this page clearly illustrates the principles of the instrument. A serious defect of this type of instrument is that the field of vision is too limited. The man at the wheel is able to see under normal conditions only that which lies immediately before the boat. It is true that he can turn the periscope about so as to look in other directions, but this, of course, involves considerable inconvenience. On at least two occasions has a submarine boat been run down by a vessel coming up behind it. [Illustration] ~SEEING IN ALL DIRECTIONS AT ONCE~ As long as the submarine has but a single eye it would seem quite essential to make this eye all-seeing; and since the two lamentable accidents just referred to, an inventor in England has devised a periscope which provides a view in all directions at the same time. This has been attempted before, but it has been found very difficult to obtain an annular lens mirror which would project the image down the periscope tube without distortion. The accompanying illustrations show how this difficulty has now been overcome. While we will not attempt to enter into a mathematical explanation of the precise form of the mirror lens, it will suffice to state that it is an annular prism. The prism is a zonal section of a sphere with a conoidal central opening and a slightly concave base. All the surfaces, however, are generated by arcs of circles owing to the mechanical inconvenience of producing truly hyperboloidal surfaces. The lens mirror is shown in section at _A_ in Fig. 1. The arrows indicate roughly the course of the rays into the lens and their reflection from the surface _B_, which is preferably silvered. The tube is provided with two objectives _C_ and _D_ (Fig. 3) between which a condenser _E_ is interposed at the image plane of the lens _C_. At the bottom of the periscope tube the rays are reflected by means of a prism _F_ into the eyepiece. Two eyepieces are employed. One of lower power, _G_, is a Kelner eyepiece, the purpose of which is to permit inspection of the whole image, while a high-powered eccentrically placed Huyghenian eyepiece, _H_, enables one to inspect portions of the image. The two eyepieces are mounted in a rectilinear chamber, _I_, which may be rotated about the prism at the end of the periscope, thus bringing one or other of the eyepieces into active position. The plan view, Fig. 4, shows in full lines the high-powered eyepiece in operative position, while the dotted lines indicate the parts moved about to bring the low-powered eyepiece into use. A small catch, _J_, shown in Fig. 2, serves to hold the chamber in either of these two positions. The high-powered eyepiece is mounted on a plate, _K_, which may be rotated to bring the eyepiece into position for inspecting any desired portions of the annular image. The parts are so arranged that when the eyepiece is in its uppermost position, as indicated by full lines in Fig. 2, the observer can see that which is directly in front of the submarine, and when the eyepiece is in its low position, as indicated by dotted lines, he sees objects to the rear of the submarine. With the eyepiece at the right or at the left he sees objects at the right or left, respectively, of the submarine. The high-powered eyepiece is slightly inclined, so that the image may be viewed normally and to equal advantage in all parts. Mounted above a plain unsilvered portion of the mirror is a scale of degrees which appears just outside of the annular image. A scale is also engraved on the plate _K_ with a fixed pointer on the chamber, making it possible to locate the position of any object and rotate the plate _K_ so as to bring the eyepiece _H_ on it. The scale also makes it possible to locate the object with respect to the boat. [Illustration: HOW WE LOOK THROUGH A PERISCOPE THE PERISCOPE TOP.] [Illustration: PERISCOPE IN GENERAL USE.] [Illustration: THE UNIVERSAL OBSERVATION LENS.] This improved periscope is applicable not only to submarine boats but for other purposes as well, such as photographic land surface work, in which the entire surroundings may be recorded in a single photograph. The accompanying photograph, taken through a periscope of this type, shows the advantages of this arrangement and gives an idea of its value to the submarine observer when using the low-powered eyepiece. Of course, by using the other eyepiece any particular part of the view may be enlarged and examined in detail. [Illustration: INSIDE OF A MINE-PLANTING SUBMARINE MINE-PLANTING SUBMERSIBLE. A Lake type vessel designed for planting contact mines. In naval warfare it is sometimes of advantage to plant mines, either to defend harbors, or in some cases the mines are planted in the course of the approaching enemy. This is a vessel designed for that purpose. The enemy is seen approaching, and the mine-planting submarine runs in ahead of them in a submerged condition and drops a number of contact mines on their course; the enemy strikes the mine and is blown up. A number of vessels were blown up by contact mines of this type in the Russian-Japanese war.] Accidents and Their Causes. The accidents which submarine vessels must guard against are as follows: collision, foundering, explosions and asphyxiation. The first danger is, however, no greater than those to which vessels that run entirely on the surface of the water are exposed. The eye of the submarine places the commander on a practical level with the commander of other vessels, so that if a collision occurs it is due to the same lack of watchfulness which causes collisions on the surface of the water. The submarine boat is less liable to founder than an ordinary vessel, because she is built to withstand a greater pressure of water than other kinds of vessels. Of course, if a submarine springs a leak, she is in grave danger of sinking to the bottom, and there is less chance of the crew being rescued from a submarine, because no one but those on board know of the danger if the boat is under the water. How Explosions May Occur. In submarine vessels explosions may occur either through a collection of gases from the batteries or by reason of leaks in the pipes or tanks of the fuel supply system, or through the bursting of the air flasks belonging to the boat, or the air reservoirs in the automobile torpedoes. The greatest danger is from explosive gases and have been the cause of all explosions in modern submarine craft, and the greatest danger in this connection is the liability of a leak in the gasolene pipes or tanks. This gas is a heavy gas and so goes to the bottom of the vessel, where it is not so easily detected as a gas which rises. There is no certain way of guarding against leaks of gasolene. A leak may occur at any time in a pipe or tank of gasolene through some cause or other no matter how carefully inspected, and the gas from this is so active that it will go through the tiniest hole imaginable--even through a hole which water will not penetrate. The crew of a submarine is always subject to this danger unless the tanks are built outside the hull of the ship. How the Air May Become Poisoned. There is a constant danger of asphyxiation to the men in the submarine. A very small leakage of gas or the exhaust from an internal combustion engine may make the air so impure that those aboard will be overcome. A great deal of care must be taken to keep the air pure and to warn the crew at the first sign of danger from this. When submarines first came into practical use, it was found a good idea to take a number of little white mice down with the vessel to warn all if the air began to become impure. As soon as this occurred, the mice became distressed and squealed as loudly as they could, thus warning those aboard the ship of danger. The mice felt the impurity of the air quicker than the men, not because they had any special gift to discover when the air was bad, but because they breathe much more quickly than man--take shorter and many more breaths. Now, however, a chemical device has been invented which is affected in such a way as to ring a loud bell, if the air in the vessel becomes impure to such an extent that there is any danger. Breathing the same air over and over may fill the vessel with carbonic acid gas. There should be no great danger from this, however, as submarines are now built sufficiently large to provide enough actually pure air for each man aboard for forty-eight hours, and it is hardly conceivable that a submarine need be submerged more than half that length of time under any conditions. Of course, then, too, there is the danger of accident due to carelessness or ignorance. In other words, it is just as difficult to make a fool-proof submarine as a fool-proof anything else. Wherever anything is constantly dependent upon the continuous careful attention of human beings, there is constant danger of accident, whether it be on board a submarine, a railroad train, steamship or in connection with anything else. [Illustration: A SUBMARINE UNDER THE ICE UNDER-ICE SUBMARINE TORPEDO BOAT. Submarine designed to navigate submerged under the ice, in ice-bound countries. Vessels of this type could enter harbors and destroy the enemy’s shipping at will. A vessel of this type would also be of value in transporting mails, passengers and cargoes between ice-bound ports where navigation by surface vessels is closed for several months in the year.] Story of How the Submarine Has Been Developed. It is only within the past twenty years that man has been able to successfully navigate under the surface of the water. ~WHO MADE THE FIRST SUBMARINE BOAT?~ It has been a dream of inventors and engineers for the past three hundred years. During the reign of King James I. a crude submarine vessel was built of wood, and was designed to be propelled by oars extending out through holes in the side of the vessel, the water being prevented from coming in through the openings by goat skins tied about the oars and nailed to the sides of the boat, which made a water-tight joint, but at the same time gave flexibility to the oars, so that by feathering them on the return stroke they could be manipulated to give head motion. Very little, if any, success could have attended this effort. Nearly a hundred years later a man by the name of Day built a submarine and made a wager that he could descend to 100 yards and remain there 24 hours. He built a boat and submerged it in a place where there was a depth of 100 yards. He succeeded in remaining the 24 hours, and according to latest advices is still there, as he never returned to the surface. There is very little information as to the construction of these early craft. The first really serious attempt at submarine navigation was made by a Connecticut man, a Dr. David Bushnell, who lived at Saybrook during the Revolutionary War. He built a small submarine vessel which he called the “American Turtle,” and with it he expected to destroy the British fleet, anchored off New York during its occupation by General Washington and the Continental Army. Thatcher’s Military Journal gives a description of this vessel and describes an attempt to sink the British frigate “Eagle” of 64 guns by attaching a torpedo to the bottom of the ship by means of a screw manipulated from the interior of this submarine vessel. A sergeant who operated the “Turtle” succeeded in getting under the British vessel, but the screw which was to hold the torpedo in place came in contact with an iron scrap, refused to enter, and the implement of destruction floated down stream, where its clockwork mechanism finally caused it to explode, throwing a column of water high in the air and creating consternation among the shipping in the harbor. Skippers were so badly frightened that they slipped their cables and went down to Sandy Hook. General Washington complimented Dr. Bushnell on having so nearly accomplished the destruction of the frigate. If the performance of Bushnell’s “Turtle” was such as described, it seems strange that our new government did not immediately take up his ideas and make an appropriation for further experiments in the same line. When the attack was made on the “Eagle,” Dr. Bushnell’s brother, who was to have manned the craft, was sick, and a sergeant who undertook the task was not sufficiently acquainted with the operation to succeed in attaching the torpedo to the bottom of the frigate. Had he succeeded the “Eagle” would undoubtedly have been destroyed and the event would have added the name of another “hero” to history and might then have changed the entire art of naval warfare. Instead of Bushnell being encouraged in his plans, however, they were bitterly opposed by the naval authorities. His treatment was such as finally to compel him to leave the country, but he returned after some years of wandering, and under an assumed name, settled in Georgia, where he spent his remaining days practicing his profession. Robert Fulton, the man whose genius made steam navigation a success, was the next to turn his attention to submarine boats, and submarine warfare by submerged mines. A large part of his life was devoted to the solution of this problem. He went to France with his project and interested Napoleon Bonaparte, who became his patron and who was the means of securing sufficient funds to build a boat which was called the “Nautilus.” With this vessel Fulton made numerous descents, and it is reported that he covered 500 yards in a submerged run of seven minutes. ~HOW SUBMARINES WERE DEVELOPED~ In the spring of 1801 he took the “Nautilus” to Brest, and experimented with her for some time. He and three companions descended in the harbor to a depth of 25 feet and remained one hour, but he found the hull would not stand the pressure of a greater depth. They were in total darkness during the whole time, but afterward he fitted his craft with a glass window 1¹⁄₂ inches in diameter, through which he could see to count the minutes on his watch. He also discovered during his trials that the mariner’s compass pointed equally as true under water as above it. His experiments led him to believe that he could build a submarine vessel with which he could swim under the surface and destroy any man-of-war afloat. When he came before the French Admiralty, however, he was met with blunt refusal, one bluff old French admiral saying: “Thank God, France still fights her battles on the surface, not beneath it,” a sentiment which apparently has changed since those days, as France now has a large fleet of submarines. After several years of unsuccessful efforts in France to get his plans adopted, Fulton finally went over to England and interested William Pitt, then chancellor, in his schemes. He built a boat there, and succeeded in attaching a torpedo beneath a condemned brig provided for the purpose, blowing her up in the presence of an immense throng. Pitt induced Fulton to sell his boat to the English government and not bring it to the attention of any other nation, thus recognizing the fact that if this type of vessel should be made entirely successful, England would lose her supremacy as the “Mistress of the Seas.” Fulton consented to do so, but would not pledge himself regarding his own country, stating that if his country should become engaged in war, no pledge could be given that would prevent him from offering his services in any way which would be for its benefit. The English Government paid him $75,000 for this concession. Fulton then returned to New York and built the “Clermont” and other steamboats, but did not entirely give up his ideas of submarine navigation, and at the time of his death was at work on plans for a much larger boat. Fulton had a true conception of the result of submarine warfare, and in a letter he says: “Gunpowder has within the last three hundred years totally changed the art of war, and all my reflections have led me to believe that this application of it will, in a few years, put a stop to maritime wars, give that liberty on the seas which has been long and anxiously desired by every good man, and secure to Americans that liberty of commerce, tranquillity, and independence which will enable citizens to apply their mental and corporeal facilities to useful and humane pursuits, to the improvement of our country and the happiness of the whole people.” After Fulton’s death spasmodic attempts were made by various inventors looking to the solving of the difficult problem, but no very serious efforts were put forth until the period of the Civil War, and then a number of submarine boats were built by the Confederates. These boats were commonly called “Davids,” and it was one of them that sank the United States steamship “Housatonic” in Charleston Harbor on the night of the 17th of February, 1864. This submarine vessel drowned four different crews, a total of thirty men, during her brief career. At the time she sank the “Housatonic” her attack was anticipated, and sharp lookout was kept at all times; but, notwithstanding their vigilance, she succeeded in getting sufficiently close to plant a torpedo on the end of a spar, and sink this fine, new ship of 1400 tons displacement. It will be seen from the above description that these vessels, while able to go under water, were not controllable. After the Civil War several other inventors took up the problem of trying to design a submarine vessel that could be controlled as to maintenance of depth and direction under water. In Europe, Gustave Zede, Goubet and Drzwiezki, and in this country Mr. Baker and Mr. John P. Holland, built experimental vessels. In 1877 Mr. Holland built a small boat which was called the “Fenian Ram.” It is stated that this vessel was built with capital furnished by the “Clan-na-Gael,” with the idea of using it against the British fleet in an attempt to free Ireland. While some slight success was met with by these inventors, it was not until about 1897 that any real progress was made. ~THE FIRST SUCCESSFUL SUBMARINE WITH HYDROPLANES~ In 1893, Simon Lake, an American inventor, submitted plans to the United States Naval authorities at Washington for a submarine boat that would navigate between the surface and the bottom by the use of what he called “hydroplanes,” which were designed to cause the vessel to submerge on an even keel. Mr. Lake’s design of vessel was also provided with wheels to enable it to navigate on the water bed. It was also provided with a diving compartment to enable the crew to don diving suits and leave the vessel, in working on wrecks, cutting cables, planting mines, etc. In 1904 and 1905 he built a small vessel to demonstrate his principles and succeeded in successfully navigating the vessel on the bottom of New York Bay. He then built a larger vessel of about 50 tons displacement for further experimental purposes. This vessel was called the “Argonaut,” and was built in Baltimore in 1906 and 1907. This boat was successful from the start and covered thousands of miles in the Chesapeake Bay and along the Atlantic Coast, New York Bay and Long Island Sound, and was the first successful submarine boat to navigate in the open sea and on the water bed of the ocean. Mr. Holland had, in 1894, received a contract for a submarine vessel for the United States Navy, and her construction was started in 1895. This vessel was called the “Plunger.” This was the first official recognition given to a submarine boat in the United States. The Government of France had also given an order for a submarine boat which was under construction at this period. The “Plunger” was never submerged, her construction covering a period of several years, and she was finally abandoned. Mr. Holland had, however, in the meantime prepared the designs of another vessel which he called “The Holland.” This vessel was accepted by the United States Government in 1900, and a number of other vessels of this type were built. These vessels were known as submarines of the diving type. They were controlled by means of a horizontal and vertical rudder placed at the stern of the vessel and the boat was, by means of these rudders, inclined down by the bow, and driven under the water by the force of their screw propeller. England also built a number of submarines of the diving type. In 1901 Mr. Lake brought out a larger vessel of his type, which was controlled by hydroplanes, which vessel was sold to the Russian Government, was shipped across the Atlantic to Kronstadt, and from there by rail to Vladivostok, and was in commission off Vladivostok just before the close of the Russian-Japanese War. Mr. Lake then received orders from the Russian and other Governments for a number of additional boats of the even keel type, to be controlled by hydroplanes. Mr. Lake’s principles of control have been now generally adopted by all Governments, as providing the safest and most reliable means of control of the vessel when navigating under the surface. The United States Government has recently adopted this type to be built in their Navy Yards, and most other builders have adopted the hydroplanes as the means of maintaining depth when running beneath the surface. [Illustration: CLEARING A CHANNEL OF BUOYANT MINES This is one of the services to which submarine boats of this type lend themselves with peculiar fitness. It is possible for them to carry on this work with deliberation and to success, under the very guns and searchlights of a vigilant foe, without the slightest danger of being detected. This would be accomplished preferably by the co-operation of two boats. They would take opposite sides in the channel, with a connecting rope extending out through the diving compartment. It is obvious that as they move along the rope will sweep the whole mine-field and gather in the connecting cables. This would be indicated at once to the operators in the diving compartment by the load upon the sweeping line. A grapple may then be attached to the rope and sent out of one boat and hauled into the other, and thus drag the mine so near that a diver could go out and destroy its electrical connections or cut it adrift. Should the latter operation be the aim, the grapple may be so fashioned as to accomplish this without the diver leaving the compartment. This latter method is one strongly recommended by some of the most prominent military authorities on submarine defense.] [Illustration: This picture indicates the manner in which the boats have traveled many miles over all kinds of bottom. In the present instance the boat is shown systematically searching the bottom with her diving door open and strong lights being used to facilitate a more perfect examination. There is no trim or equilibrium to maintain. When the propelling machinery stops the boat comes to rest. A cyclometer attached to these wheels gives a fairly reliable reading of the distance traveled under normal circumstances. As the currents do not carry her out of her course, and as her gauges give an absolute record of changing depths, it is possible to so navigate upon the bottom with remarkable precision. In shallow waters this method has many advantages.] [Illustration: A MACHINE WHICH MAKES THE DIVER’S TASK EASY SHOWING TUBE HANDLING CARGO IN SUNKEN SHIP.] Recovering Cargo or Submerged Objects Without the Aid of Divers. The operating tube is here shown within the body of a hulk and co-operating with the lifting derrick on the surface craft in the removal of the submerged cargo. A grab-dredge bucket of well-known construction is used, the jaws of which, when being lowered by one rope, open, and when strain is brought on the lifting rope, the jaws close. The working end of the tube is placed in the immediate neighborhood of the cargo to be lifted and, as the grab is being lowered from the boat above, the operator in the compartment controls the grab by means of the guide line shown attached to the small derrick boom, and leads it directly over the cargo to be lifted. The grab is then dropped and the signal sent to the vessel above to hoist. The moment the lifting line tautens the bucket grasps a load and fills itself with material in the manner common to this type of dredge. This method of directing intelligently and deliberately the dredge bucket may be applied as well to the removal of rock or any other obstruction or to any of those various services of kindred character familiar to submarine engineers. The great and prime advantage of the system is the fact that no divers are required, and the work is under the perfect control of an operator subject only to atmospheric pressure. In consequence, therefore, the only limit to the effective operating of this apparatus is the length of the tube, and, as has been said, this can be made long enough to reach depths denied to the diver simply by interposing additional sections. [Illustration: LIFE ABOARD A SUBMARINE LIVING QUARTERS ABOARD A SUBMARINE.] Where Do Sponges Come From? Until within comparatively recent years, the sponge was regarded as a plant; it is now known to belong to the animal kingdom, and to the order spongida of the class of rhizopoda. Sponge is an elastic, porous substance, formed of interlaced horny fibers, which produce by their numerous inosculations, a rude sort of network, with meshes or pores of unequal sizes, and usually of a square or angulated shape. Besides these pores there are some circular holes of large size scattered over the surface of most sponges, which lead into sinuous canals that permeate their interior in every direction. The oscula, canals, and pores, communicate freely together. The characteristic property of the sponge is the facility with which it absorbs a large quantity of any fluid, more especially of water, which is retained amid the meshes until forced out again by a sufficient degree of compression, when the sponge returns to its former bulk. From this peculiarity, combined with its pleasant softness, arises the value of the sponge for the purposes to which it is applied. In domestic economy and in surgical practice, there is no other product that can be satisfactorily substituted for it. Sponge is an aquatic production, indigenous to almost every sea and shore. It is abundant and varied between the tropics, but becomes less so in temperate latitudes and continues to diminish in quantity, variety, and size, as it is traced into European and colder seas, until it almost disappears in the vicinity of the polar circles. Some sponges are known to be hermaphrodite, but that the individual at one period produces chiefly male elements, and later, chiefly female elements. Fertilization takes place in the body of the mother, and the egg here undergoes its early development. The embryo eventually bursts the maternal tissue and, passing into one of the canals, is caught by the current sweeping through the canal system and is discharged into the surrounding water through one of the large apertures on the surface of the sponge. In the Bahama Islands and along the coast of Florida, the breeding time of many sponges covers the period from mid-summer on through early Autumn. There is propagation sometimes by ciliated gemmules, yellowish and oval, arising from the sarcode mass, and carried out by the currents. These are mostly formed in the spring, and after swimming freely about for a time, become fixed and grow. In its natural state, the sponge is a very different looking object from the article of commerce. The entire surface is covered with a thin, slimy skin, usually of a dark color, and perforated to correspond with the apertures of the canals. The sponge of commerce is in reality only the home or the skeleton of the sponge. There are a few sponges that inhabit ponds and sluggish rivers; the others are marine. Of these, many of the calcareous and siliceous kinds inhabit the shores between tide-marks, preferring a site near the low ebb, where, nevertheless, they are daily alternately submerged, and left exposed to the atmosphere. The figured sponges with a fibrous texture, to whatever genus they belong, are denizens of deeper water, and are never left uncovered. They grow usually in groups, on rock shells, shellfish, corallines, and seaweeds, and either have no power of selection, or the quality of the site is indifferent to them. How Do Sponges Grow? In their growth, some sponges assume a determinate figure or at least one whose variations are confined within certain limits. The greater number are irregular and variable, their shape depending in a great measure upon the peculiarities of their state, to which they easily accommodate themselves. They will incrust a shell, or a crab, a rock, or seaweed, following every projection and sinuosity. The offshoots will spring up with a more luxuriant growth in the deeper sheltered places until the original shape of the foundation they grow upon is lost to sight. Sponges are unmoving and inirritable. They never remain rooted to the places of the germination, and are incapable either of contracting or dilating themselves or even of moving any fiber or portion of their mass. The functions which distinguish them as living beings are few, and faintly imaged. How Do Sponges Eat? Although sponges lack the power of motion possessed by most animals, being nearly always attached, in one position or another, to some object, the study of their habits in captivity brings out many of their animal characteristics in a striking manner. Small specimens taken from the sea and placed in dishes of salt water may be kept alive for several hours if well cared for; and by using finely powdered coloring matter, such as carmine or indigo, the manner of their feeding may be readily observed. Sponges are more active in fresh sea water than in stale; they cannot be kept alive out of water and soon die if exposed to the air. Being unable to go in search of food, as a natural result, they can grow only in places where there is always an abundance of food suited to their wants. The great sponging grounds of the world are wholly confined within waters having a relatively high temperature during the entire year. The Old World sponges grow principally in the Mediterranean and the Red seas; the New World sponges are found about the Bahamas, southern and western Florida, and parts of the West Indies. The finest sponges come from the East, but one of the American species, the so-called “sheep’s wool,” stands high in favor. The commercial sponges are separated into six species, three of which are European and three American. They are all referred to a single genus called spongia, and though having much in common as regards structure, their texture varies to such an extent as to make them of very unequal value for domestic purposes. The Old World species may be arranged as follows, in order of their grade of excellence, beginning with the best quality: The Turkey cup sponge, Levant toilet sponge, the horse, honey comb, or bath sponge, and the Zimoca sponge. The American species include the sheep’s wool sponge, the yellow glove, violet, and grass, sponges. A very close relationship exists between the species of the two continents. All known regions in which useful specimens abound contribute to the world’s supply. The trade is extensive. The demands upon the fisheries are great. In the Mediterranean, the fishing is carried on in some places at a depth of forty fathoms. Divers, naked, or in armor, go down to the bottom and tear off the sponges from their places of growth. In some places drag dredges are employed. How Are Sponges Caught? In the past quarter-century the sponge-fishery of the Florida coast has grown remarkably. Its headquarters is at Key West and several hundred sailing vessels are engaged in the industry. The fishing appliances consist of a small boat, a long hook, and a waterglass. The hook is in reality a three-pronged spear attached to a pole thirty-five feet long. In searching for sponge the fishers row about in the small boat. By holding the glass on the surface of the water the bottom is plainly seen and small objects are readily discerned. When a sponge is sighted the pole with the hook attached is shot down and the product deftly gathered. The boat-load is brought to the deck of the schooner, allowed to remain there a few hours, and then is carried down into the hold. On Friday nights, the fishing generally ends for the week, and the vessel sails for some spot on the neighboring coast where there are established crawls, or places for curing the catch. These crawls are about 8 x 10 feet square, their purpose being to hold the sponges while maceration and decomposition take place. The resulting refuse is carried off by the tide. The fishermen go away for another catch and the sponges are left in the crawls until the end of the following week when a new cargo is brought in. The returning fishermen beat the decomposed sponges with clubs, removing the impurities. The water is squeezed out, then the sponges are allowed to dry on the ground. After drying, the hold of the large vessel is loaded to the utmost with the product and the voyage to Key West is made. Buyers from New York look over the sponges, and make offers for entire cargoes. The fishermen dispose of their goods rapidly and sail away for more. The buyers store the sponges in some dry building, and cause them to be bleached by lime. A popular manner of bleaching is to wash the sponges thoroughly in water, and then to immerse them in diluted hydrochloric acid to dissolve any of the calcareous substance. Having again been washed they are placed in another bath of dilute hydrochloric acid to which six per cent. of hyposulphite of soda, dissolved in a little warm water, has been added. In this bath the sponges remain for twenty-four hours, or until the bleaching process is completed. After bleaching, the sponges are pressed until their bulk is greatly reduced; they are then baled, and shipped to New York, which is the distributing point for the entire Florida product. Sponges are by far the most important fishery products of Florida, representing about one-third of the annual value of the fishing industry. In 1899, the yield was over 350,000 pounds of sponges of which the first value was nearly $400,000. Why Does Yeast Make Bread Rise? There is a lot of sugar in the dough from which bread is made. Sugar contains three things--carbon, hydrogen and oxygen. When sugar is fermented it amounts practically to burning it. To make good bread from the dough it is necessary to ferment the sugar which is in the ingredients from which it is made. Yeast, which is a simple living plant, has the power to ferment sugar. When sugar ferments, two things are produced. One thing is the formation of carbonic acid gas. A great deal of this carbonic acid gas is caught in the dough in the form of large or small bubbles and some of it escapes into the air. The other part tries to escape into the air also but cannot, and causes the dough to rise, which makes the bread light, as we say. The holes you see in the bread after it is baked are the little pockets where the carbonic acid gas was retained in the dough. These bubbles of gas all through the dough act like a lot of little balloons and lift the dough up with themselves as they try to get to the top and escape into the air. What Is Yeast? Yeast is a living plant that is used for the purpose of causing fermentation. The yeast we use in baking bread is an artificial yeast--really a dough made of flour and a little common yeast and made into small cakes and dried. If kept free from moisture it retains the power of causing fermentation for some time. The flour and other matter in a cake of yeast are only used to keep the yeast in a form where it can be preserved. It is necessary to add water to start fermentation and that is why we add hot water when we stir in the yeast for a baking. Is a Moth Attracted By a Light? It seems to be a strange contradiction of the nature of living things that a moth should fly deliberately into a light or dash itself to death against the glass surrounding a strong light. This is contrary to the usual law of nature which gives the living thing an instinct to protect itself against enemies. For a long time we thought that moths did not deliberately burn themselves up by flying right into a light, but our naturalists have proven that not only moths but certain birds, bees, flies and butterflies, burn themselves up by flying into the flame of a light or fire. [Illustration: HOW MAN LEARNED TO MAKE A FIRE SAWING This was probably man’s first method of producing fire. By rubbing two sticks together in this way sufficient heat was produced to set fire to easily burnable material such as dried grass, etc.] [Illustration: DRILLING An improvement came when man learned that by twirling a dry stick in a hole in another piece of dry wood the fire could be started more quickly.] How Man Discovered Fire Fire was probably one of man’s first, if not the first, great discoveries, and has been one of his greatest servants as well as one of his greatest dangers. We do not know who discovered fire, or what nation first used it. It is, however, one of the signs that distinguishes man from the other animals. Not any of the lower animals was acquainted with the use of fire, while probably the earliest races of mankind seem to have been acquainted with it. Mythology tells us wonderful stories of the origin of fire: according to these tales it was stolen from the sun, or the gods, and given to man; and Pandora, the first woman, was sent down to earth to punish man for his theft. The most popular of these stories is the legend of Prometheus. According to this legend, fire, in the early days, was under the exclusive control of the gods. Prometheus, brother of Atlas, the god who supported the world on his shoulders, determined that the use of fire should be given to the people. He decided by some means to send a spark of fire to the earth, believing that one spark caught by man would start a burning flame that would never go out. With this idea in mind, Prometheus visited Zeus, the great ruler, to carry out his purpose, for Zeus controlled fire. While Zeus was not looking, Prometheus “stole some brands of fire from the hearth, which he hid in the stalk of a fennel and sent it down to the earth.” Through this Prometheus gave to man his first knowledge of fire. But while this story of fire may or may not be true, the use of fire rests entirely with man and his ingenuity. Through his ingenuity man was able to subject fire to his will; making it perform certain of his labors; and to a certain extent making it his servant; although it always did and always will get beyond his control at times. Our ancestors were not satisfied with preserving the fire which the gods gave them; they tried and succeeded in producing it. One day one of them discovered that by rubbing two sticks together rapidly, the friction would create a fire. It was a most useful discovery. Before long the whole of mankind had learned this trick; others improved on this crude method until step by step men learned that by striking two pieces of flint or other hard mineral together, quicker action was obtained. [Illustration: DRILLING WITH BOW STRING Man’s ingenuity soon taught him that if he tied one end of a string to something and wrapped it around his drilling stick, one end of which was in a hole as in the first drilling picture, he could increase the rapidity of making fire.] [Illustration: DRILLING WITH HELP With some other to hold the drilling stick while he operated the string he was able to produce fire more quickly than he had ever done before.] All kinds of methods were devised to increase knowledge of producing fire. The early Greeks found out how to catch the rays of the sun on a burning-glass and produce fire; the Romans achieved the same results through the use of mirrors. [Illustration: PLOWING This is another method man used for rubbing two pieces of wood together. In following this plan he usually used one stick of bamboo and rubbed it back and forth in a slot he had made in another piece of bamboo.] [Illustration: FLINT AND PYRITES In some places it was discovered that if you struck a piece of hard stone, like flint, against another, a spark was produced which could be caught on a bunch of dry grass or moss and so start a fire.] In about A.D. 900, an Arab, named Bechel, discovered phosphorus, but it took almost 800 years more for Haukwitz to learn that when phosphorus was brought into friction with sulphur, fire would result. In another hundred years the world was benefited by the invention of the friction match--and since that time about one-half the people have been carrying matches about with them, able thus to start a fire easily any time. ~FIRE A MARK OF CIVILIZATION~ Fire and man’s knowledge of it have had much to do with man’s progress in civilization. Before man had fire, his life and movements were much like those of other animals. When man had learned to make a fire he was free to move and live anywhere and, therefore, people began to cover more territory. [Illustration: THE FLINT AND STEEL METHOD OF MAKING FIRE THE INTRODUCTION OF THE FLINT AND STEEL METHOD Because fire was so important to him, man kept on trying to make this task easier. He finally contrived a tinder box when iron and steel became known. The tinder box is where he kept his flint and the piece of steel which he struck upon the flint. He also kept in the box pieces of cloth or paper on which he caught the sparks so produced.] [Illustration: PISTOL TINDER BOX This is a picture of a tinder box in the form of a pistol. It enabled man to produce sparks in greater numbers and more rapidly.] [Illustration: PRODUCING SPARK WITH FLINT AND STEEL This shows the method for striking the piece of steel against the flint to make the sparks fall on the cloth or paper in the box.] [Illustration: A COMPLETE TINDER BOX SET This picture shows a very complete tinder box set used by the wealthy people in the old days. A man carried this outfit with him just as today he carries matches.] [Illustration: This tinder box set is very neat and compact. It is said still to be used among the Himalayan tribes where it was discovered.] [Illustration: THE FIRST MATCHES THE OXYMURIATE MATCH This match, the first, was introduced in 1505. It was a slip of wood tipped with a chemical mixture. To light it it was necessary to stick its head into a bottle containing acid.] [Illustration: PROMETHEAN MATCH This was a paper cigarette dipped in a mixture of sugar and potash. Rolled within the paper was a tiny glass bulb filled with sulphuric acid. To light the match you pressed the bulb with pincers hard enough to break the bulb. This released the acid which set fire to the paper.] What Would We Do Without Matches? If one were to ask the man in the street what invention of the nineteenth century is his most constant and invaluable ally he might be mystified for the moment, but the undoubted answer would surely come in the single word “Matches.” These familiar objects, apart from their luxurious use by smokers, are the indispensable servants of mankind from the moment of rising in the morning till the household is wrapped in sleep, and it is to them we turn when disturbed in the hours of darkness. [Illustration: FIRST LUCIFER MATCH Invented by John Walker in 1827. It consisted of a stick of wood tipped with sulphur and then with a chlorate mixture. To ignite it the match was drawn rapidly through a folded piece of sandpaper.] [Illustration: MODERN SAFETY MATCH The first practical match was made less than a century ago.] No doubt “familiarity breeds contempt,” and it is difficult to imagine how man would fare, bereft of his box of matches. It might help the world to realize how much it owes to the inventors of the Lucifer Match, were it possible to cut off the supply of these magic fire producers for only one brief day. It requires no very vivid imagination to picture the consternation and confusion that such a step would produce, and there is a grim humor in wondering how the primitive methods of obtaining a light would serve the public convenience in these days of strenuous hustle. Seeing that fire has been employed by man since prehistoric days, one would expect that easy means of obtaining it would have been devised in the early ages. We find, however, that until the beginning of the nineteenth century nothing in the nature of a match was available, and the crudest methods were still in use. We know from Virgil that in the reign of the Emperor Titus fire was obtained by rubbing decayed wood with a roll of sulphur between two stones, but it is not till Saxon times that we have evidence of the use of the tinder box with its flint and steel. That this latter was still regarded as something remarkable, as late as the fifteenth century, is proved by its representation in the collar of the Order of the Golden Fleece, which was founded in