IC-NRLF ST LESSONS ON NATURAL IIIILOSOPHY, PART SECOND HABTFOBD: TLLIAM j. HAMEBSLEY, PUFLISHEF. THE LIBRARY OF THE UNIVERSITY OF CALIFORNIA PRESENTED BY PROF. CHARLES A. KOFOID AND MRS. PRUDENCE W. KOFOID FIRST LESSONS NATUBAL PHILOSOPHY, FOR CHILDREN. |n PART SECOND. BY MARY A. SWJJT. NEW EDITION, ENLARGED AND IMPROVED. HARTFORD: WILLIAM J. HAMERSLEY, PUBLISHER. PHILADELPHIA J. B L1PPINCOTT & CO. 1862. V ENTERED according to Act of Congress, in the year 1859, "by WILLIAM J. HAMERSLET, In the Clerk's Office of the District Court of the United States for the District of Connecticut. R. H. HOBBS, STEREOTYPER AND ELECTROTYPER. THE favorable reception given to the " FIRST PART OF LESSONS ABOUT NATURAL PHILOSOPHY," encouraged the writer to offer to parents and teach- ers of primary schools, the "SECOND PART." It was received with the same approbation ex- tended to its predecessor, and is now respectfully presented in an enlarged and improved form. M35S76S t HAT does Natural Philos- ophy teach us ? It teaches us about the matter that all bod- ies are made of, and about the properties of bodies. What is a BODY ? A body is any thing made of matter. You have learned about the Attraction of Cohesion is this property found in all bodies? It is ; but it is stronger in some bodies than it is in others. In what bodies is it the strongest ? In hard bodies. 6 BODIES. Do we call hard bodies by any other name ? We call them solid bodies, or solids. Can you mention some solid bodies ? Wood, and stone, and iron are solid bodies. Are cork and sponge solid bodies ? They are. But they are SOFT bodies are SOFT bodies solids ? They are. Why are some solids HARD, and other solids soft? ^ Because the attraction of cohesion is stronger in hard bodies than in soft bodies. What do you mean by the attraction of co- hesion ? The attraction of cohesion is the power of sticking together, which God has given to the little particles of bodies. If you make clay and dough into any shape, why will they remain in that shape ? Because they are solid bodies. LIQUIDS. Why could you not make milk and oil into any shape ? Because they are not solid bodies. What are they called ? They are called Liquids. If I should place a solid and a liquid upon a table, how could' you tell which was the SOLID ? The solid would remain upon the table as you placed it. What would the LIQUID do ? It would flow on the table, or down from the table to the floor. Why would the liquid act so differently from the solid ? Because the attraction of cohesion is so much stronger in the solid, and keeps the particles close together. Do the particles of liquids attract each other at all ? They do. How do we know they do ? If I dip my finger in a liquid, when I take 8 FLUIDS. it out, a drop will stay on the -end of my finger. What makes the shape of drops of rain and dew ? The attraction of cohesion, that draws to- gether the little particles of water. What is a LIQUID? A Liquid is something that flows like water. Have liquids any other name ? They have ; they are sometimes called Fluids. Do all FLUIDS flow like water 1 Not all ; there are some fluids that are dif- ferent from water and oil. Are steam and air solids ? They are not. How do you know they are not ? Because they do not keep their place, and can not be made into any shape. Are they liquids ? They are not. How do you knorv they are not ? FLUIDS. 9 Because they do not flow down to the ground, like water. What are such bodies as air and steam called ? They are called Aeriform fluids. What is the meaning of AERIFORM ? Air- form. Why is steam called aeriform ? Because it is like air. Can you tell the difference between liquids and aeriform fluids ? Liquids only move in one direction, that is, downward, from a higher to a lower place. How do fluids like air move ? They can move as easily in one direction as in another. What fluids do we see move upward? The fog rises up, and helps to form the clouds, and steam rises from the engine and floats away. How is it with smoke ? 10 FLUIDS. DENSITY. Smoke rises from the chimney, and flames rise from burning bodies. How many kinds of fluids are there ? Two ; liquids and aeriform fluids. Then how many kinds of BODIES are there ? Three ; solids, liquids, and aeriform bod- ies. What do we call HEAVY solid bodies ? We call them dense bodies. DENSITY. RARITY. H What is DENSITY ? Density means heaviness. What bodies are dense ? Those bodies whose particles are close to- gether, are dense. What causes their particles to cling together so closely ? The attraction of cohesion. Can you mention some DENSE bodies ? Gold, and iron, and stones are dense. Which has the greatest density, iron or wood ? Iron has the greatest density ; it is the heaviest. What do we call light solid bodies ? We call them rare, or thin bodies. What is RARITY ? Rarity is thinness, or lightness. What bodies are RARE ? Those bodies whose particles are not at- tracted strongly together. Can you mention any such bodies ? 12 RARITY. Cork and sponge are rare bodies. How do you know they are ? They are light, and can be cut apart more easily than iron can. F you throw a hollow In- dia rubber ball upon the floor, will it lie there ? It will not; it will bound up into the air. What makes it bound It is full of air ; and the air in it makes it bound. Would it not bound up if it was filled with something besides air ? It would, but not near so high as it does when full of air. Will you tell me how the air can do this ? When I throw down the ball, the side that 14 AIR. ELASTICITY. touches the floor is flattened or bent in, and does not leave as much room for the air in- side of it. What becomes of the air in it, then ? The particles of air are pressed together so closely that they do not take up as much room as they did before. What presses them together so closely ? The striking of the ball against the floor, when you throw the ball upon the floor. How long will the air in the ball stay-in so small a place ? Not a moment. What will it do ? It will instantly spring back, and press out the flat side of the ball as round as it was before. What will the ball do then ? It will bound up from the floor. What is the springing of the air called ? It is called Elasticity. ELASTICITY. 15 When we say the air has the power of springing back, what do we mean to say ? We mean to say that the air is elastic. What other bodies are elastic ? Every body that springs back to its first shape, when it has been pressed in or struck, is an elastic body. Can you mention some bodies that are elastic ? Ivory, wood, and many other hard bodies are elastic. What bodies are not elastic ? Clay and wax are not elastic. How can you tell whether a body is elastic ? By striking it against another body. What will it do if it is elastic ? It will bound back, without seeming to be flattened or bent inward. How will it be if it is not elastic ? It will not bound back again, but will be flattened. How do you know that the air we breathe is elastic ? 16 ELASTICITY. THE BENT BOW. If the air in the ball is elastic, the air out of the ball must be elastic too. When you stretch a piece of India rubber, what makes it spring back as soon as you let it go ? Its elasticity. If you pull out the string of a bow, what will happen to the bow ? It will bend. What if you let go the string ? The bow will straighten, as it was before. Why will it straighten ? Because the wood of which the bow is made is elastic. ELASTIC FLUIDS. 17 Why do you pull the string hard when you fix the arrow to it ? So that the arrow may fly the farther. What makes the arrow fly off when you let go the string ? The bow is bent when I put on the arrow, and, the moment I let go the string, the bow springs back so quickly that it straightens the string with a jerk, and the arrow is sent into the air. Now can you tell me what it is that makes the arrow fly off from the bow ? It is the elasticity of the bow. You said the air is a fluid then are fluids elastic ? Some fluids are. What fluids are elastic ? Aeriform fluids are called elastic fluids. 2 F you can easily bend any body you hold in your hands, as you can a piece of steel spring or a wire, what do you say of that body? Sa 7 it inflexible. What is the meaning of FLEX- IBLE? Flexible means easily bent. But if, instead of BENDING, it should BREAK what kind of a body should you call it I should call it brittle. What do you mean by a BRITTLE body ? I mean a body that easily breaks. FLEXIBILITY. MALLEABILITY. 19 Mention some BRITTLE bodies. Glass and china are brittle, ice is brittle, stones are brittle, and so are some metals. What bodies are flexible ? Tin, lead, India rubber, thin plates of most metals, and wires. Could any one, hammer out, or roll out, gold and silver into thin plates ? He could, with heavy hammers or machines. When any metal can be hammered out thin- ner, without breaking, what do we call it ? We call it malleable or hammer-able. Is CHALK malleable ? It is not. How do you know ? If I strike it with a hammer, it breaks in pieces, instead of spreading out thin. Then what do you say of chalk ? I say it is brittle. How thin can gold and silver be rolled out, or hammered ? Till they are thinner than paper. 20 MALLEABILITY. TENACITY. What are they then called ? Gold-leaf and silver-leaf. How thin can gold-leaf be made ? So thin that three hundred and sixty thou- sand leaves of it, when all laid together in a pile, would be only an inch thick. Of what use is such thin gold-leaf? It is used to cover looking-glass and pic- ture frames, and to put upon wood, or leather, or paper. When any thing is covered with gold-leaf, what do we call it ? We call it gilt or gilded wood or paper. When a metal can be stretched out, like a wire, to a great length, without breaking, what is it that keeps it from breaking ? Its tenacity. What is the meaning ef TENACITY ? Tenacity means its power of holding to- gether. Then has WIRE great tenacity ? It has. SUSPENSION. 21 Can you tell about any tiling that shows the wonderful tenacity of IRON-WIRE ? Very strong bridges are made across some rivers, for the heavy locomotive and cars to go safely across, and yet these bridges hang on wires of iron. What is the name of such bridges ? They are called suspension bridges. What is the meaning of SUSPENSION ? Hanging; for they hang upon wires. the 22 SUSPENSION. How are the wires fastened each side of the river ? A strong tower is built on each bank of the river, and the long, large wires pass over the towers, and are fastened firmly into the ground beyond. fmirt|. HEN you say a body is MOVING, what do you mean ? I mean that the body is changing its place. Then what is the meaning of the word MOTION ? Motion means change of place. When your ball moves along the floor, what PUTS it in motion ? My hand. When the arrow flew through the air, what put it in motion ? The springing of the bow made it fly off Then what puts bodies in motion ? The power of the body that strikes, or pushes, or draws them, puts them in motion. 24: FORCE. ATTRACTION. What is this power called ? It is called force. What put the arrow in motion ? The force of the elasticity of the bow. How do you know ? If the bow had not been elastic, the arrow would never have left the string. What can stop the motion of a body? The power or force of something else can make it stop. What makes an arrow stop moving, after it has been shot into the air ? If it falls to the ground, it is the force of the attraction of gravitation that brings it down. If it goes into a tree or a board, what force stops it then ? The force of the cohesive attraction of the particles of wood stops it How does the cohesive attraction stop it ? It keeps the particles of wood so closely together that the arrow can not separate them. MOTION. 25 When the wood will not permit the arrow to go through it, what do we say the wood does ? We say the wood resists the arrow. Which is it that resists the arrow, the particles of wood, or the cohesive attraction that draws the particles together ? It is the attraction of cohesion. How do you know ? If the cohesion could be taken from the wood, the arrow would pass through it. When you throw a ball into the air, will it move all the time as fast as it did when you first threw it? It will not, but will go slower and slower, till it falls. When the motion of a lody becomes slower and slower, what do we call such motion ? We call it retarded motion. What is the meaning of RETARDED ? Any thing is retarded that goes slower and slower. 26 MOTION. If you were running, how could you RETARD your motion? By beginning to walk. If you were walking, and should begin to run, and should, continue to run faster and faster, what kind of motion would that be ? It would be accelerated motion. What do you mean by ACCELERATED motion? Quickened motion. If you were walking, and should not go any faster or any slower, * what motion would that be? It would be uniform motion. What is meant by UNIFORM motion ? Motion that is always alike, never slower or faster. Mention some body that always moves alike. The minute-hand of a watch, and all the wheels in a watch, move just as fast at one time as they do at another. Then what is the motion of a watch ? It is uniform motion. MOTION. 27 When a ball is falling to the ground, what is its motion ? It is accelerated motion. Why is it accelerated 1 Because the attraction of trie earth draws it more and more, the nearer it comes to the earth, and this makes the ball fall faster and faster. When you throw up a loll, what is its motion ? It is retarded motion. 28 MOTION. Why is it retarded motion ? Because the attraction of the earth draws it down when my hand sends it up, and this makes the ball go slower and slower, till it finally falls to the ground. How many kinds of motion have you men- tioned ? Three. What are they called ? Retarded motion, accelerated motion and uniform motion. How does a body move when its motion is retarded ? Slower and slower. How when its motion is accelerated ? Faster and faster. How when its motion is uniform ? Neither faster nor slower, but always alike. When you say a ball ASCENDS, what do you mean ? I mean that the ball goes up, or rises. MOTION. 29 When a body DESCENDS, what does it do ? It goes down, or falls What kind of motion does a "body have by being thrown upward ? Retarded motion; because it rises slower and slower. What is the motion of this body when it descends ? Accelerated motion; because it falls quicker and quicker. What is the motion of water when it is fall- ing in a cataract ? It is accelerated motion. Which has the greatest weight, a cannon ball or a bullet ? A cannon ball. If you could throw a cannon ball against a thin board, would it go through the board It would not. If a bullet should be shot out of a gun, would it go through the board ? It would. 30 STRENGTH. WEIGHT. VELOCITY. Why would the bullet go through, when the cannon-ball, which is much heavier, would not ? Because the bullet goes so much faster than the ball. What is swift motion called ? Velocity. Then why will the bullet go through the board, when the ball will not ? Because the weight and velocity of the bullet together, is greater than the weight and velocity of the ball, when put together. When weight and velocity are put together, what is the whole called ? The momentum of the body. Which momentum is greatest, then, that of a cannon-ball thrown by the hand, or that of a bullet fired from a gun ? That of the bullet. How could you increase the momentum of the cannon-ball ? By firing it from a cannon. HEN you throw a ball against the wall, what becomes of the ball ? It will bound back, as if the wall threw it back to me. What is its motion from the wall bach to you called ? It is called reflected motion. What is meant by REFLECTED motion ? The motion made by throwing back any thing. What is the meaning of the word REFLECT ? It means to throw back again. Then, when I say a body is reflected, what do I mean ? 32 COMPOUND MOTION. You mean that the body is thrown back again. If I should strike a ball to make it go one way, and you should strike it at the same time to make it go another way, what would its motion be called ? It would be called compound motion. Why would it be called COMPOUND motion ? Because it would be two motions put together. What two motions would it be ? The motion which your hand gave it, and the motion which my hand gave it at the same time. Which way would the ~ball move if we struck it together 1 It would not go the way your hand sent it, nor the way my hand sent it, but it would move between those ways. In what kind of a LINE does the ball move after being struck by both our hands ? In a straight line. RECTILINEAR MOTION. 33 What is the motion of the ball called ? It is called rectilinear motion. What is the meaning of RECTI-LINEAR ? Straight line. Here is a diagram which will show you how the ball would move. When you hold a string that is tied to a ball, and swing the ball round, what is the motion of the ball? It is circular motion. Why is it called CIRCULAR motion ? Because the ball moves round in a circle. What is the motion of the earth around the sun called ? It is called circular motion. 3 34 CIRCULAR MOTION. Why? Because tlie earth moves in a circle around the sun. Here is a diagram which shows you what circular motion is. If you throw your ball forward, will it fall down -to the ground in a straight line ? No ; it will make a curved line, like the diagram. CURVILINEAR MOTION. 35 What then is the motion of the ball called ? It is called curvilinear motion. What is the meaning of CURVILINEAR? Curved line. Then what is curvilinear motion ? Motion in a curved line. What makes the ball move in a curved line ? My hand sends it straight forward, and the attraction of the earth draws it straight down. Then which way will the ball move ? It can not go either way, but goes between. Then is curvilinear motion compound motion? It is. Why ? Because it is the motion made by my hand and the attraction of gravitation to- gether. Is circular motion compound motion also 1 It is. Why ? 36 MOTION. FORCE. Because it is made by throwing- the ball into the air, while at the same time you keep it from going off by holding the string. Why is one kind of compound motion REC- TILINEAR and another CURVILINEAR ? When both of the hands or forces are taken away as soon as they have struck the ball, it will move in a straight line. Then what motion will the ball have ? Rectilinear motion. How will it be, when one force continues to move the ball after the. oilier is removed ? The motion will be in a curved line, or curvilinear. When you throw a ball straight forward, what force continues to move the ball after it leaves your hand ? The attraction of the earth draws it to the ground in a curved line. How is the circular motion of the earth com- pound motion too ? The centrifugal force makes it go from the MOTION. FORCE. 37 center, and the centripetal force draws it to the center. To what center ? The sun ; because the earth moves round the sun. tart !j> p^ HEN a pendulum to a clock swings backward and forward, does it move in a straight line ? It does not ; the line is curved, like a part of a circle. Why does it not swing quite around the place where it is fastened, just as the ball does when you whirl it round your hand. ? The attraction of gravitation draws the pendulum down toward the ground when it begins to go up. Then why does not the pendulum stop, in- stead of going up the other side ? ATTRACTION OF GRAVITATION. 39 Because it goes down so fast that it can not stop in an instant. What is this like ? Like a boy sliding down hill. 40 ATTRACTION OF GRAVITATION. How does he go ? He goes so fast down the hill, that when he gets to the bottom he can not stop, but goes part way up the next before the sled stands still. How would it be, if he should slide down the second hill ? He would go part of the way again up the first. And how is this like a pendulum ? When my hand draws aside the pendulum, and then lets it go again, the attraction of gravitation draws it down as far as it can ; ATTRACTION OP GRAVITATION. 41 and, because it can not stop itself, it will go up the other side. What will it do then ? The earth will draw it down again so fast, as to send it up the side from which it started. What is a favorite amusement of the Rus- sians ? Sliding down ice-hills. How is an ice-hill made ? It is made of wood, covered with water frozen to ice ; it has three ascents, one above another, with a little valley between each ascent. How do they slide down this ice-hill ? At the top of the hill they seat themselves on a sled made for the purpose, and slide down the first ascent very swiftly. Will the sled stop there ? It will not. Why will it not ? Because it came down so fast, that it will 42 ATTRACTION OF GRAVITATION. slide acrovss the little valley and up to the top of the next ascent ; and then down that, in the same manner. What keeps a pendulum of a dock in motion all the time? The wheels that are inside of the clock. What makes the wheels move ? The weights that draw the strings that are fastened to the wheels. How long will the pendulum swing before it stops ? Till the wheels stop moving. How long will. the wheels move around? Till the weights reach the bottom of the clock. How can they be put in motion again ? By winding up the strings that fasten the weights to the wheels. What makes the weights go down to the bot- tom of the clock ? The attraction of gravitation. What is the attraction of gravitation ? ATTRACTION OF GRAVITATION. 43 The attraction of the earth. Then, when a clock goes, what does the attraction of gravitation do to make it go? It keeps the wheels in motion, and thus helps to keep the pendulum swinging. How fast does a pendulum commonly swing backward and forward ? Once in every second, which would make sixty times every minute. Can any thing be made to move forever with- out stopping ? No, nothing. Has any one ever tried to make a body move forever ? Yes ; many have tried, but they could not do it. If a body should move forever, what would its motion be called ? Perpetual motion. What is the meaning of PERPETUAL ? Perpetual means never-ending. 44 PERPETUAL MOTION". Then what is perpetual motion ? Never-ending motion. How many motions have you learned about ? Eight. What is the first? Retarded motion, or motion that becomes slower and slower, as if a boy stopped run- ning and began to walk. What is the second ? Accelerated motion, or motion that becomes faster and faster, as if he began to run again. The third? Uniform motion, or motion that is always alike, like a clock. The fourth? Reflected motion, or moving back again like a ball bounding back from a wall. The fifth? Compound motion, or two motions together. The sixth? MOTION. 45 Circular motion, or motion in a circle, like swinging a ball tied to a string. The seventh ? Curvilinear motion, or motion in a curved line. The eighth? Perpetual motion, or motion that will never stop. ow 6?o children play at SEE-SAW? They take a plank of wood, and lay it across a block or a fence, and then one sits on each end, and they swing up and down the see-saw. What is a plank sometimes called ? It is called a lever. What is a lever ? A rod or plank that will not bend easily is a lever. What is the block that it rests upon called ? It is called a fulcrum. What is a fulcrum ? THE LEVER. 47 That which the lever or plank stands upon, when its ends are moving^up and down. If the plank were laid across a fence, when you play at see-saw, what would be its ful- crum ? That part of the fence that it lies across. What are the parts of the lever each side of the fulcrum sometimes called? They are called arms of the lever. Then, if you were playing at see-saw, where would the arms of the lever be ? I should sit on one arm of the lever, and my companion would sit on the other arm. 48 THE LEVER. If you are just as heavy as your companion, where must the block, or the fulcrum of the plank, be placed? Exactly in the middle, so that one .arm may be just as long as the other. Then, if you sat still upon the plank, would it move up and down? Each arm would exactly balance the other, and it would stand still. When do bodies balance each other ? When one is just as heavy as the other. If your companion is twice as heavy as you are, how must the plank be placed on the ful- crum ? So that the arm on which I sit may be almost twice as long as hers. Where would the fulcrum be, then? Near my companion. What POWER sets the lever in motion up and down ? We are the power ; because I strike my feet on the ground, so as to send myself up, THE LEVER. 49 and that makes my companion go down ; and then she does the same, and goes up while I go down. If a stone much heavier than yourself should be placed on one arm of the lever, how could you raise up the stone ? By putting the fulcrum so near it, that the arm on which the stone lies would be very short, and the other very long. Would you have to use much strength to raise it, then ? I should not, if the long arm was very heavy. Why would you not ? Because the long arm would be so heavy, that it would almost raise the stone on the other arm of itself. Then what is the use of the lever ? It assists us in raising large and heavy bodies. In raising the stone, what was the power ? My hand. 50 THE LEVER, What was the weight ? The stone. What was the fulcrum ? The block upon which the lever rested. Where was the fulcrum placed ? Between the power and the weight, or be- tween the hand and the stone. Is a pair of scissors like a lever ? Yes ; it is two levers, fastened together. Do both levers move the same way ? No ; when one moves up, the other goes down, till they meet together. What is the fulcrum of each lever ? They both have the same fulcrum. THE LEVER. 51 What is it? Each lies across the other, and they are fastened together, where they cross, by a small rivet or screw that goes through them. Then what is the fulcrum of the scis- sors ? The rivet that fastens the scissors together. What is the power that moves these levers ? My hand. What is the weight ? If I am cutting paper, the paper is the weight. Will you tell me why the paper is the weight ? - Because, when I am cutting it, I lift up the paper with the lever which my thumb draws 52 THE LEVER. down, and I press clown the paper with the lever which my fingers draw up. How will this cut the paper ? The levers are screwed so tight to each other, that when they come together there is no room for the paper between them. What becomes of the paper, then ? One part of the paper remains on one side of the scissors, and the other part is on the other side, and the scissors are between them. Then what have the scissors done to the paper ? They have divided it. Are the scissors the same kiftd of lever as the see-saw ? They are. How do you know they are ? Because, in them both, the power is at one end, the weight at the other, and the fulcrum between. HEN a merchant weighs out a pound of sugar, how does he do it ? He takes a pair of scales, or balances, like those in this picture, puts a piece of lead, that weighs exactly a pound, into one of the scales. 54 THE LEVER. Then what does he do with the sugar ? He puts just as much sugar into the other scale as will lift up the weight in the first scale. How can he tell when he has put in a pound of sugar ? When one scale is just as heavy as the other, then the sugar is weighed right. Are these scales like a lever ? Yes, they are a lever. Which is the fulcrum ? The place where they are hung up is the fulcrum. What is the weight ? The lead in one scale. What is the power that raises the lead ? The sugar in the other scale. Then, is not the lever very useful ? It is ; it would be very difficult for us to do many things without the lever. HEN you open a door, which is the weight that you move 1 The door is the weight. What is the fulcrum? The hinges are the fulcrum. What is the power ? My hand. Is the door such a kind of lever as the see- saw? It is not Why is it not ? Because the weight is between the power and the fulcrum. 56 THE LEVER. How is it with the see- saw ? The fulcrum is between the power and the weight. Is there any other kind of lever ? There is one more. What is it ? It is a lever which has the power between the weight and the fulcrum Have you ever seen such a lever ? Yes ; when I have seen a man raising a ladder against the wall. THE LEVEE. 57 What was the fulcrum ? The ground, on which the bottom of the ladder rests. What the weight ? The ladder. I What was the power ? The strength of his hands. Then how many kinds of levers are there ? Three kinds. What is the first ? One where the fulcrum is between the power and the weight as the see-saw. 58 WHEEL AND AXLE. What the second ? One where the weight is between the power and the fulcrum as the door. What the third ? Where the power is between the fulcrum and the weight as a man raising a ladder. What is another means of raising weights besides the lever ? The wheel and axle. What is the shape of a wheel ? It is round, like a hoop, with sticks, called spokes, going from the outside to the center. What is the axle of a wheel ? The place where the spokes are fastened in the center of the wheel. WHEEL AND AXLE. 59 Here is a picture of a wheel and axle. What is the use of a wheel and axle ? It is used to raise weights. Have you ever seen a wheel and axle used in raising a weight ? Some wells have a wheel and axle to raise up the bucket of water out of them. How is it done ? The rope or chain on which the bucket hangs is fastened to the axle, and so, when 50 "WHEEL AND AXLE. the wheel turns around, the .rope winds around the axle till the bucket comes up. Can you tell how a wheel and axle is like a lever 1 The spokes are the long arms of the lever, and the parts of them that go into the axle are the short arms. Cm tip HY will a ball roll down ^ upon the floor, if you place it upon a desk ? Because the desk is not level, like a table, but inclines downward. What may a desk then be called? An inclined plane. What is a plane ? A smooth surface. What is an INCLINED PLANE ? A smooth surface, that slopes or inclines downward. What is the use of an inclined plane ? It is used to raise weights. How is a weight raised easier by an inclined plane than without it ? 62 INCLINED PLANE. If we put one end of a long board upon a wagon, and let the other rest upon the ground, and roll a barrel up the board into the wagon, we shall find it much easier than it would be to lift it straight up from the ground into the wagon. Here is a picture of an inclined plane, with a weight rolling up upon it. What is the shape of the blade of a knife? It is like two inclined planes, put together. What would the blade of a knife be called in Philosophy 1 It would be called a wedge. WEDGE. 68 What is a WEDGE ? It is like two inclined planes, put together, so as to have a sharp edge on one side, where they meet. Here is a picture of a wedge in a log. Of what use is a wedge ? A wedge is used for cutting or dividing things. 64 SCREW. Mention the names of some wedges. A knife is a wedge, and so is an axe, and almost all cutting instruments are wedges. Have you ever seen a screw ? I have, very often. Where have you seen them ? A pair of scissors is fastened together with a little screw, and hinges and locks are fas- tened upon doors with screws. Why are not nails as good as screws to fasten them with? A nail might be pulled out ; but the sharp edge, that rises and winds around the screw, keeps it in tight, just where it is fastened. PULLEY. 65 What is a screw like ? It is much like a round nail, with a sharp wedge wound around it. Of what use is the sharp edge or wedge around the screw ? It cuts the wood where it goes in, while we are turning it, and holds the screw in its place. Here is the picture of a screw. What is a PULLEY ? A pulley is a little wheel and axle, with its edge hollowed out, so as to make a place for a cord to wind around it. 5 66 PULLEY. Here is one, with a cord upon it. Of what use is a pulley ? Weights are raised by means of pulleys, and removed to other places. How do they help people to raise weights 1 The weight is fastened to one end of the cord, and a person can raise the weight by pulling down the other end of the cord. How are buckets of water sometimes raised out of a well ? A rope is put over a large pulley, that is fixed above the well, and a bucket is fastened to each end of this rope. PULLEY. 67 When one bucket is filled in the well, how is it easily brought up ? By drawing down the other bucket. Why does it require so little strength to do this ? Because the weight of the empty bucket helps to draw down that end of the rope, and raise the full bucket at the other end. How many kinds of pulleys are there ? Two ; the fixed pulley and the moveable pulley. 68 PULLEY. What is afxed pulley ? A pulley that turns round, but remains fixed in the same place. What is a moveable pulley ? A pulley that is constantly moving from some place, as it turns round. ess ait w HAT are the lever, wheel, pulley, inclined plane, wedge, and screw called in Philosophy ? They are called me- chanical powers, hat do you mean by mechan- ical powers ? The power of machines or instruments. Of what use are the mechanical powers ? They help us to raise and move very large weights, and to divide and cut hard bodies into any shape we please. Can you mention some useful machines ? Clocks and watches, locomotives and steam engines, are useful machines. 70 MOVING POWER. Of what use are steamboats ? They carry very heavy loads of goods and people across the water, much faster than vessels can. ' How can they do this ? By means of the machinery in them. What keeps the machinery in motion ? The power of the steam. MOVING POWER. 71 How can the cars on railroads move so very rapidly ? It is by means of the power in the loco- motive engine, that draws them. Does steam keep these machines in motion ? It does. What do you mean by MACHINE or MA- CHINERY? When several instruments or mechanical powers are put together, we call the whole a machine or machinery. What did you say kept the machinery of steamboats in motion ? The power of the steam. I 72 MOVING POWER, What is steam called when it moves ma- chinery ? It is called a moving power. Then what is the moving power of steam- boats ? Steam. What is the moving power of railroad cars ? Steam. What is the moving power of a clock ? Gravitation. How do you know ? It is gravitation which draws down the weights, that turn the wheels, and keep the clock going. In mills and manufactories upon the banks of rivers, what is the moving power ? The water. How do you know ? It is the water running upon the great wheels that keeps them turning; because, when the stream is very low, or almost dry, the wheels stop turning. MOVING POWER. 73 Is water the moving power of all mills? No ; the moving power of some mills is wind. What are such mills called ? Windmills. When animals or men move machines, what do we say the moving power of such machines or instruments is ? Animal strength, or the strength of men and animals, is their moving power. Who has provided the moving powers of all machines ? The Creator of the world. 74 MOVING POWER. What good have they done for man? They save him from much very hard labor. How do they do this ? With a machine, one man can do the work that would require all the strength of many men to do, without it Can you mention one example ? In cotton factories, where cotton cloth is made, they have machines to card, and spin, and weave ; so that a very few persons can make hundreds or thousands of yards of cloth in a day, from cotton that is brought in, the same morning. Can you mention anotlwr example ? On railroads, a little steam-engine can draw CURIOUS CLOCKS. 75 a great many heavily loaded cars thirty miles in one hour. Who teaches man how to save his labor by contriving these machines ? Our Creator How does he teach us ? He made the wood and iron of which ma- chines are made; and the wind, and water, and strength, that moves them ; and He teaches the mind in us to think and contrive how to use these things. Can you describe a machine so curious that it could never have been made without a great deal of thinking and contriving ? A man in England made two clocks, and sold them to some gentlemen, who sent them as a present to the Emperor of China. Each clock was in the shape of a little chariot. A very small lady sits gracefully in it. Her right hand is leaning upon the chariot. Under her hand is a curious little clock, about as large as a quarter of a dollar. This clock strikes 76 CURIOUS CLOCKS. every hour, and will go eight days without being wound up. Upon the lady's finger sits a beautiful little bird, adorned with diamonds and rubies. Its tiny wings are spread out ready to fly, arid if a diamond button below it is touched, the bird will flutter for some time. What makes the bird move ? Its little body is fall of very small wheels, which make it move. How large is the whole body of the bird ? About the size of a pea. Can you tell any thing more about the clock- chariot ? The lady holds in her left hand a gold tube, no larger than a large pin. On the top of this tube is a small round box. Around this box is a ring, made with gold and diamonds, not larger than a ten cent piece. This ring goes round and round the box, three hours at a time without stopping. Can you tell what is over the lady's head ? There are two small umbrellas, standing CURIOUS CLOCKS. 77 upon a pillar no larger than a quill. Under the largest umbrella is a little bell, which strikes every hour. At the lady's feet is a golden dog, and before it are two little birds, fastened upon springs. Their wings and feathers are very brilliant with precious stones, and they seem to be flying away with the chariot. How can the chariot move along ? By means of springs and wheels, that are out of sight. If they are touched, they can make the chariot go straight forward, or in a circle, or in any way that you wish. What is behind the chariot ? A little golden boy, taking hold of it, and seeming to push it along. Above the um- brella are flowers and ornaments of precious stones ; and at the top of the whole stands a \\ttlzflyingdragvn, made of the same brilliant stones. What good lesson should we learn from this story ? 78 CURIOUS CLOCKS. That the man who made these wonderful docks had great skill; and that God, who made the man. and gave him so much skill, must be more skillful than all the men in the world more skillful than we can think. Ctodftfr. HIGH would a sled slide down most easily, a hill of sand or a hill of ice ? The hill of ice. Why would it slide most easily over that ? Because sand is rougher than ice. Then does the roughness of the sand hinder the sled from sliding down ? It does. What is the name that philosophers give to this roughness, when bodies are rubbing against each other ? They call it friction. 80 FRICTION. Which can you turn, most easily, a rusty lock or a bright one ? The bright one. Then, which lock has most friction ? The rusty one. Why will a person slip down upon ice, and not upon stone or earth ? Because there is more friction when his feet rub against the stone than when they rub against the ice. How could the rusty lock be made to turn as easily as a bright one ? By oiling it. Why would oiling it make it turn easily ? It would take away some of the friction. How would it take away the friction ? By making the iron smooth. Can you mention another example of fric- tion? I have heard carriage wheels creak, be- cause they needed greasing at the axle. Why do people grease carriage wheels ? FRICTION. 81 To make them smooth, and turn easily around the axle. Why will the grease make them turn easily ? It destroys some of the friction. Why do drivers of carriages, when going down steep mountains, fasten one of the wheels, so that it can not turn ? 6 82 FRICTION.' To increase the friction of the wheel, and prevent the carriage from going down so fast. What does INCREASING THE FRICTION mean ? Making it more difficult for the wheels to go down hill. Horv many kinds of friction are there ? Two. What are they called ? The dragging and the rolling friction. Can you mention an example of dragging friction ? The chained carriage wheel, dragged down the hill. What is an example of rolling friction ? Wheels, when they are turning or rolling. When the walks are covered with ice, why is it difficult to walk upon them without slip- ping ? Because there is not friction enough. FRICTION. 83 What would happen to us if there were no friction ? We could not walk a step before we should begin to slip along very fast, and could not easily stop ourselves. How do people increase the friction when the walks are covered with ice ? They throw sand, or ashes, or something rough, upon them. Could you hold any thing in your hand if there were no friction ? Not without difficulty. Why? Because it would slip through so easily. 84 FRICTION. Then, is not friction very useful ? It is ; for I could not hold my knife and fork, or book, very easily, without friction. How do people travel from Mount Cents, in Europe, to the town of Laneburg ? On the top of the steep, snowy precipice the traveler gets into a sledge, and slides down so swiftly, that he goes three miles in seven or eight minutes, and his breath is almost taken away from him by the motion. What makes him go down so fast ? The ice is so smooth that there is scarcely an} 7 friction when the sledge glides over it. Why is it much easier to travel and to carry heavy loads upon snow than upon the ground ? Because the snow is so very smooth, that the friction is almost destroyed, and the run- ners slide along more easily than wheels roll along the ground. fcssan Cfjirtenttfp o you recollect what you learned about springs? I learned that they I were made by the water, under ground, bursting out at the top. When a spring bursts out a little while, and then stops, and then goes on again, and continues stopping and going on, what is it called ? It is called an intermitting spring. What is the meaning of INTERMITTING ? Any thing that sometimes goes and some- times stops is called intermitting. Can you tell what is the cause of intermit- ting springs 1 They stop or intermit, at times, because 86 SPRINGS. there is not always enough water under the ground to keep them running. Why are not all springs intermitting springs ? Because some basins are so large that they are never empty, from one rain to another. Does the rain make all springs ? It does not. What besides rain causes springs ? The springs which are near those mount- ains that are always covered with snow, are made by the melted snow. What would become of the water that flows from the springs, if there should be mountains and hills all around them ? They would fill up the valley between the hills, and this would form a lake. Where would the water go, when the valley was filled up with it ? It would flow out of the first opening it could find, and become a river. LAKES. 87 What can you tell about Lake Geneva. The river Rhone ran down from the mount- ains, till it came to this valley made by the high hills all around it, and there it stayed till it had filled it and found an opening, and then the river ran on to the ocean. What is this valley full of water called now? Lake Geneva; and it is a beautiful lake, among the mountains of Switzerland. Then what is a lake ? A valley full of water. Are lakes always full of water ? They are not always ; some are dry part of the year. Can you mention any ? Lake Merom is such a lake, in Palestine. What can you say of lake Merom ? It is a small lake, made by the river Jordan, When the snows on Mount Lebanon melt, and run down in the Jordan, this lake is full, and is several miles long ; but, when the hot weather comes on, it dries up. 88 LAKES. Do you know of any other such lake ? In Germany there is one called Zirknitz (pronounced Tzeerkneetz,) lake. Will you describe it ? It is four or five miles in length, and about two miles wide. All around it are wooded mountains, in which live deer, wild boars, and hares. A part of the year the people come here in boats to fish, and the other part they may sow and reap grain, and hunt these animals, at the bottom of the lake. Can you tell about a very curious rvay of fishing these people have ? When the water goes out of the lake, it runs through about forty holes at the bottom, carrying the fish with it. This makes so many little whirlpools. When the water has all run through, the peasants go down with lights into one of these cavities. This cavity or hole is several feet under the bottom of the lake, in a solid rock. Here the water runs down again, through small holes, as LAKES. through a seive, and the poor fishes are left behind for the peasants to catch Can you mention any more remarkable ac- counts about this lake ? Sometimes, when it begins to rain hard, three of these cavities spout up water to the hight of twelve or eighteen feet. If the rain continues, the water will bubble out of the holes through which it had run, and the whole lake will fill again in a single day. HAT very remarkable lake do you read of in the Bible ? Lake Asphaltites, or, as it was often called, the Dead Sea. What do you know about this lake ? It is supposed to have been caused by the destruction of Sodom and Gomorrah. How does it differ from other lakes ? The water in it tastes salt, and different from sea-water. What is found mixed with the water, to give 'it such a taste ? Salt, and magnesia, and bitumen. OILY SPRINGS. 91 What is bitumen like ? It looks like hard coal, and burns like tar. Do you know of any other wonderful lake in Asia ? In the northern part of Asia is a large lake, which throws up a liquid, which the people collect, and put in their lamps to hurn. Are there any springs in the world that throw up such liquids ? In Italy there are oily springs. What can you say of them ? Their surfaces are covered with oil, that smells very fragrant when it is burning, and is of different colors. How much oil is collected from some of these springs ? From one spring, near the Appenine mount- ains, which comes out of a rock, people can collect twelve pounds in one week. What is the name of this rock oil ? Petroleum. 92 OILY SPRINGS. What is the meaning of the word PETROLEUM ? Petre means rocks, and oleum means oil. Why is it called rock oil ? Because it comes up from rocks. Is this oil ever found upon the sea ? It is found in the sea, near mount Vesuvius. How does it first show itself on the water? While it is rising to the top of the sea, the water seems to be covered with bubbles. How do people gather it ? They skim it off, as they sit in their boats, and then put it into pots and jars. Does this petroleum rise to the top of the water all the time ? It rises only in warm weather. What different colors has the oil? Some is white, some yellow, some red, and some black. Which oil is the lest ? The white, clear oil. Which is poorest ? The black ; because it is not pure. BOILING SPRINGS. 93 Are there any springs of petroleum in this country ? There is one in Kentucky. Do you know of any other kinds of springs, besides the oily springs, and springs of good water ? In Iceland there are boiling springs. jSSr Why are they called boiling springs ? Because they are as hot as boiling water. 94 MINERAL SPRINGS. Are they of any use to the people of Ice- land ? The Icelanders boil and cook their food with them. What other springs have you heard of? Warm springs. Why are they called warm springs ? Because the water that comes up from them is always warm. Where are any warm springs ? In Virginia. What very useful springs are found in the United Slates? Mineral springs. Why are they called mineral springs ? Because they have sulphur, and iron, and salt, and other minerals in them. Have they any different name ? They are often called medicinal springs. Why are they called medicinal springs ? Because they cure diseases, as medicine does. HOT SPRINGS. COLD SPRINGS. 95 Can you mention the names of some of these springs ? There are Ballston and Saratoga Springs, in the State of New York, and Yellow Springs, in Ohio, and many others in different States. What curious springs are sometimes found in the sea, near the shore ? Springs of fresh water. How can it be got, without mixing it with the salt sea-water 1 A bottle, corked tight, can be let down di- rectly over the spring, and, when it is low enough, the cork can be drawn out, and the fresh water will instantly fill the bottle, which can then be drawn up. What are HOT springs ? Those whose water is always hot. What are COLD springs ? Those springs which are very cold, in warm and cold weather. 96 SPRINGS. What becomes of the water that rises from springs ? It runs into streams and rivers. Where do the rivers carry their water ? Into lakes and seas, and into the ocean. Does the water of springs always run into rivers or lakes? Not always ; sometimes it disappears, be- fore it can get to a river. What becomes of it ? Sometimes it is turned to vapor, by the heat of the sun. What do we say of water, when it is turning into vapor ? We say it is evaporating. Does the water of springs ever disappear in any other way? It sometimes sinks into the earth, as the water of some lakes does. Can you tell me of one such spring ? In Palestine, near mount Lebanon, there is a spring called Phiala, because it looks like SPRINGS. 97 the mouth of a vial ; and the water from this spring goes down into the ground. Has any one ever found out what becomes of it under ground ? In the life-time of Herod the Great, the spring, and a stream that came out of the ground thirteen miles from this spring,* were examined. How did people examine them ? They knew that wood floats upon the top of water; and they threw some wood into the spring, and it went down into the ground. Was it ever seen again? The people, who were watching the stream that came out of the ground thirteen miles south of the spring, after looking some time, saw those very pieces of wood come out in it. What did this prove ? That this stream ran under ground thirteen miles. 98 SPRINGS. What is the name of this stream ? It is the river Jordan, that we read so much about in the Bible. What do you learn from this river about streams that disappear? That such streams do sometimes run into rivers, and lakes, when we think they evapo- rate. What lad effect would happen if the water was not carried off out of a lake. The water would become very bad, and fill the air with a dreadful vapor, which would make people sick. Jfiftmttfr, HEN the wind passes over stagnant lakes or pools, and carries the bad air into other places, what are such winds called? Pestilential winds. Why are they called pestilential? Because they make people, who breathe them, have a dreadful and dangerous disease, called pestilence. Are there any other remarkable winds ? There are very hot winds blowing from the deserts of Arabia and Africa. By what names are these hot winds called? Sirnoom or Samiel, and Sirocco ; they have different names in different countries. 100 WIND. What name is given to the hot south wind in Egypt? It is called Khamseen, or j/?y-days' wind. Why? Because it continues fifty days. When winds blow only at certain seasons or PERIODS of the year, what are they called? They are called periodical winds. What winds prevail in Egypt after the Khamseen is over? The rest of the year the winds are northerly. What sea is north of Egypt ? The Mediterranean sea. When the vapor rises from this sea, where do these winds carry it ? Across Egypt to Abyssinia. What becomes of the vapor, when it reaches that country? The cool air changes it to rain, which falls in torrents to the earth. INUNDATIONS. 1 01 Where does the water then go ? Some of it runs into the river Nile, and makes the river overflow its banks. What good does this river do? It passes through Egypt, where it never rains ; and, when it overflows its banks, the whole country is watered by it, How many times in a year does this river rise in this manner ? Once only. What is this overflowing of the river called ? Inundation. What would happen, if there were no such inundations. The land of Egypt would be like a desert, and nothing could grow there. Why would it be so dry and barren ? Because they have no rain, and all their water comes from this river. How does this show the KINDNESS of God? It shows that He will provide for the wants of man, in all countries where men live. 102 WHIRLWINDS. WATER-SPOUTS. How does it show His POWER ? We see, from this, that He is able to bring water where it is needed, even when it does not fall from the clouds. "He causeth the wind to blow, and the waters flow." WHIRLWINDS. WATER-SPOUTS. 1Q3 What is a WHIRLWIND? A wind that whirls very rapidly, and carries up into the air whatever is light enough to be lifted from the ground. When it passes over the sea, what happens ? It raises the water, and forms the WATER- SPOUT. How do we know that whirlwinds cause water-spouts ? A water-spout has been known to move from sea to land, and when it reached the land it became a whirlwind. When a whirlwind passes over a sandy desert, what happens? It raises the sand, arid causes the Sand- pillar that travelers speak of. Are whirlwinds ever mentioned in the Bible 1 The prophet Nahum says, " The Lord hath his way in the whirlwind, and in the storm, and the clouds are the dust of his feet." HY does smoke rise from thejire and go up through the chimney ? Because the air in the fire-place, when heat- ed, rises up arid carries smoke, which is also light, with it. When the smoke goes out of the chimney, why does it not fall to the ground ? Because the warm air, which brought the smoke from the chimney, continues to rise and carry up the smoke with it. What is this like ? It is somewhat like oil upon w r ater. Why does not the oil sink below the water ? Because the water is heavier than the oil. SPECIFIC GRAVITY. 105 If you should put the oil in the basin first, and then pour water upon it, would the oil re- main at the bottom ? It would not ; but would rise through the water, and lie upon the top of it. Why would it ? Because the water is so much heavier, that it sinks down, and crowds the oil up- ward. Why will not the smoke spread around the chimney, instead of rising higher ? Because the air above it is heavier, and crowds the light air, which is filled with smoke, upward, as the water did the oil. How high will the smoke ascend ? Till the warm and light air that carries it comes to other air that is no heavier than itself. How long will it remain there ? Till the air that carries it becomes as cool as the air around it ; and then the smoke will slowly fall to the ground. 106 BALLOONS. What makes soap-water bubbles rise in the air ? The light air that is in them. If you could fill a thin bag with very light air, and throw it into the air, as you do soap- bubbles, what would it do ? The bag would, rise. How high would it rise ? Till it came to air of its own weight. BALLOONS. 107 If you should fasten a bit of wood to it, would the bag carry up the wood with it? It would, if the wood did not make the bag as heavy or heavier than the air around it. How are balloons made? A light bag of thin silk, somewhat like a very large bubble, is filled with a kind of air lighter than the common air. How is this air kept from coming out of the bag ? The bag is lined with a varnish, made of India rubber and spirits of turpentine, so that it is air tight. How can a person go up in such balloons ? A little car is fastened to the bag, which can carry one or two persons in it How can a balloon carry a loaded car up into the air? The air in the bag or balloon is so very light that it will go up ; and, when the car, with one or two people in it, is fastened to the balloon, the whole together are so much lighter than 108 BALLOOXS. PARACHUTES. the air around them, that they can no more stay down to the earth than the hot air from the chimney can. Do accidents ever happen to those who ascend in balloons ? Very often. How? When the balloon comes down, it sometimes falls into the sea, and the people in it are in- jured or drowned ; arid sometimes it strikes a tree suddenly, or is dragged violently along the ground, and the persons in it get hurt. How can a balloon descend ? By letting out some of the light air from the bag. How will this make the bag descend ? There will be less light air in the bag, to keep up the car ; and so the balloon will be heavy, and descend. What is a parachute ? It looks like a very large umbrella, open. Of what use is a parachute ? PARACHUTES. 109 If a balloon-bag bursts, or a car upsets, and the man in it has a parachute, he can hold upon the handle of it, and keep himself from falling quickly to the ground or sea. How will the parachute hold him up ? While it is spread out, the air that it covers will support it so much that it comes down gently. How can you make a little parachute ? By fastening strings to the four corners of a sheet of paper, then bring the four strings together in the middle, and fasten a light piece of wood to them. Then what must you do? Carry it to a high place, and let it fall. 110 BIRDS. How will it fall? Very slowly indeed. If you should have an open umbrella in your hand while falling or jumping from a high place, would you fall heavily to the ground? I should not. Why? The air beneath the umbrella would support it, and so keep me from falling heavily. How do birds keep from falling, when they are up in the sky ? They spread out their wings, and the air supports them. Is this the only reason why the air supports them ? No; their bodies contain a great deal of air. How can they remain in the same place in the air, without descending at all? They strike the air beneath them with their wings a very little, and then the air reacts or strikes back again a very little, and as long as they do this they keep their places. BIRDS. HI How do they rise in the air? They strike harder against the air, arid the air reacts just as much, and sends them up higher. How do they descend? By partly shutting their wings, and letting themselves descend by their own weight. How do they know exactly what to do when they wish to rise, or descend, or stand still ? God, who made them, has taught them, and they never make a mistake, or forget how to do it. o\v are fishes able to keep themselves from sinking in water? They have fins, that spread out like the wings of a bird, and the water under them supports them, as the air supports the wings of a bird. But you said that the body of a bird had a great deal of air in it, is it so with fish? Fishes have bladders of air in their bodies, that make them lighter. How can they sink down into the water, when they wish? God has given them the power of letting out the air from the bladder. SPECIFIC GRAVITY. 113 How can they rise again? God has given them the power of filling these bladders with air again, whenever they choose. Horv do the fins of fishes differ from the wings of birds ? Their fins are not so large for them as the wings of birds are for them. Why are they not made as large ? Because water is heavier than air, and sup- ports fish better ; so that fishes need no larger fins than God has given them. How do people imitate fishes, when they wish to go into the water? They take bladders, filled with air, and fasten them around their bodies, under their arms, and the air keeps them from sinking. Do they ever use any other light body instead of blown bladders? Cork is so light that it will not sink in water, and people use it in the same way as thev do bladders. 8 114 SPECIFIC GRAVITY. What are SWIMMING-GIRDLES, AIR-JACKETS, and LIFE-PRESERVING BELTS? They are India rubber bags, filled with air, and tied around the body, instead of cork or bladders. What is the danger of using these bags? If they should slip down to the hips, the heaviest part of the body would be above them, and the body would instantly turn, so that the head would be down and the feet up, 'and the person would soon drown. What are life-boats ? Boats that contain tight cells along their sides, full of air. Why are they called life-boats ? Because they take people from a sinking ship, and thus save them from a watery grave. If you should fall into the water, what must you do first, to keep from drowning ? I must turn upon my back, and stretch my body out as straight as I can. What must you do with your hands? SPECIFIC GRAVITY. 115 I must extend them under the water, with my hands open. How must you place your feet ? I must keep them as near the top of the water as possible. How must you place your head ? I must let it drop back, so as to have the top of it nearly covered. Then what parts of your body will be above the water? Only the face and a part of the chest. What must you do then ? 116 SPECIFIC GRAVITY. I must try to breathe, so as to take more air into my body. When you throw out the air as you breathe ^ will not your body sink ? It will, a little, for an instant. What effort may you make to keep from sinking ? If I can float so, I must not make any effort, except to keep my face out, so that I can breathe. If you find your feet sinking, what must you do ? I must draw them up, and throw them out with a jerk. What might happen if you did not try to keep your feet near the top of the water ? They might sink, so as -to make my body stand in the water, and that would bring my mouth under it, and I should drown. What must you be careful NOT to do? Not to scream or struggle. When may you call for help ? SPECIFIC GRAVITY. H7 When I am a little over my fright. Who are the least likely to sink, fleshy peo- ple, or those who are not fleshy ? Those who are fleshy. Why? Because the fat part of their bodies is so much lighter than water. What amusing account can you give of Marco Paulo? Marco Paulo lived in the city of Naples, many years ago. His bones were very small, and he was very fat. His body, also, would contain a great quantity of air. These things made him so light, that he would swim on the sea like a duck. When he stood up in deep water, the water would not rise higher than his stomach. It is said that, when two men dived into the sea to drag him down with them, the moment they let him go, his body instantly rose to the surface. How can heavy bodies, like blocks of mar- 118 SPECIFIC GRAVITY. lie, be raised., when they have fallen into a har- bor or river ? By fastening casks of air to them with ropes, when the water is low. Why should the water be low ? Because the distance between the marble at the bottom, and the casks at the top of the water, would then be the shortest. How could it be raised then ? When the water rises, it will bear up the casks with it, and they will carry up the mar- ble, so that it can be taken into a boat. Why would not the boat sink, after the heavy stone was placed in it ? One reason is, because the wood of boats is so light, and they spread out over a large space on the water. F you should take a small glass tube, open at both ends, and put one end into water, what change would you see in the tube ? I should see the water rise up into the tube. What makes it rise ? The sides of the tube draw up the water in it. What kind of attraction is this called 1 Capillary attraction. What is the meaning of CAPILLARY ? Hair-like. Why is this attraction called capillary at- traction ? 120 CAPILLARY ATTRACTION. Because the bore or hole through the tube is about the size of a hair. In what tubes will water rise highest? In those that have the smallest bore or hole through them. If you take two pieces of flat glass, and put the two lower edges together, and leave the up per ones a little apart, and put the lowe? edges in water, what will happen ? The water will rise up between them. What attracts the water? The inner sides of the glass. What kind of attraction is this? Capillary attraction. If you dip one end of a piece of sponge into water, why will the water rise above that part that was dipped in? Capillary attraction makes it rise. What are the capillary tubes of sponge? The little holes that we see in it. Sponge is full of large and smali capillary tubes. What makes sponge so useful? CAPILLARY ATTRACTION. 121 It will hold a quantity of water, and will drink up water that is spilled. When such a substance as sponge drinks up a liquid, what do we say it does? We say it absorbs the liquid. Then what does sponge do to water, when put into it? It absorbs the water. Why will cotton and linen cloth absorb water? Because the cotton and linen threads, of which cloth is made, are full of pores, or very fine capillary tubes, which attract the water. If you take a bowl of water, and lay one end of a towel in it, what will happen? After some time, the towel will be perfectly wet, and the bowl will be empty. Where will the water be that was in the bowl ? It will all have run out, through the towel. How can it go from the bowl to the towel? The tubes in the linen draw the water out of the bowl. Of what use are wicks in lamps? 122 CAPILLARY ATTRACTION. They are a great number of capillary tubes, which draw up the oil from the lamp. Why must not the wick be smaller than the lamp tube? Because there would not then be tubes enough to bring up the oil. Why must not the wick be so large as to be crowded tight in the tube? If the wick was crowded very tightly, the capillary tubes in it would be closed, so that the oil could not rise through them. What happens when you dip one end of a lump of sugar into water or tea? The liquid will rise and fill the whole lump. What makes it rise? The capillary tubes in the sugar. How are large rocks sometimes split, in Ger- many ? Holes are bored in a straight line, at certain distances from each other, and wooden wedges driven into them. What is done after this ? CAPILLARY ATTRACTION. 123 Water is poured upon these wedges, and the pores or capillary tubes in them fill with water. What follows? The wedges begin to swell, and as they pour water upon them, they swell larger and larger, till they burst the rock. It is in this way that grindstones are broken off. Js capillary attraction useful in any other ways than those you have mentioned ? It causes the moisture, that is low down in the ground, to rise up through the loose earth, to the roots of plants and trees. Of what other use is it to them ? It causes the sap to ascend in trees, and to form beautiful leaves, and flowers, and fruit. Of what use is capillary attraction to our bodies ? It assists in the circulation of the blood in our bodies. When sugar, or salt, is dissolved in a liquid, what becomes of it ? 124 SOLUBLE BODIES. It is divided into such very small particles that we can not see them. How do you know that the sugar is in the water, if you can not see it? Because the water is sweet after the sugar is put in, and it was not sweet before. Does the water rise higher in the tumbler after the sugar is dissolved than it did before ? It does not. What does this prove ? That there are exceedingly small spaces between the particles of water; arid the par- ticles of sugar fill up these spaces, so that the water does not rise to make room for the sugar. What will happen when these spaces are full, if you put in more sugar ? The sugar will sink, and the water will rise in the tumbler. When water has dissolved as much sugar as it can, what do we say of it ? We say the water is saturated with sugar. If you should Jill a tumbler full of marbles , SOLUBLE BODIES. 125 could you pour sand in it without taking out the marbles ? I could. Where would the sand go ? Into the spaces between the marbles. What is supposed to be the shape of the par- ticles of water ? Round. Then, when you put sugar into water, what is it like ? It is like pouring sand into a tumbler full of marbles. How large are the particles of water ? Very small indeed. When chalk powder is put into water, will it dissolve ? It will not, but will only mix with it. How do you know it is not dissolved? , I can see it in the water, and the water, in- stead of looking clear, is thick and white. What is tlit difference between MIXING a solid in water and DISSOLVING it? 126 SOLUBLE BODIES. "When a solid is dissolved it can not be seen, neither does the water rise in the tumbler. How is it when mixed? It colors the water like itself, and makes the water rise in the tumbler. What are those bodies called which can be dissolved ? Soluble bodies, or bodies that can be dis- solved. What are those called which can not be dis- solved? Insoluble bodies. HAT instrument shows the effect of water pressure ? A hydrostatic bel- lows. If you wish to make a hijdro static bellows, what would be the first thing you would do? I should get two round pieces of board, and fasten them together with leather, so that they would rise and fall together like common bel- lows. What would you do next? I would take a long tube, and fasten it to one side of the bellows, so that the lower end of the tube would open into the bellows. How would you make the tube stand erect, after it was fixed to the bellows? 128 HYDROSTATIC BELLOWS. By bending it up from the bottom. What shape must the top of the tube be ? Like a tunnel. If a man should stand upon the bellows and pour water into the tube, what would follow? The upper side of the bellows would begin to rise, to make room for the water, and raise the man standing on it, higher and higher, till the bellows was full. What supports the man ? The water in the bellows. How can water run into the bellows, while a heavy man is standing upon it ? The water in the tube presses the water HYDROSTATIC BELLOWS. 129 at the bottom of it into the bellows, because its own downward pressure is greater than that of the man. Then what kind of pressure does the down- ward pressure of water make ? Sidewise, or lateral pressure. What is- the meaning of LATERAL? Sidewise. Then when the downward pressure of the water in the tube presses that in the bottom side- wise into the bellows, what other pressure fol- lows ? Upward pressure. What causes the upward pressure of the water ? The lateral, or sidewise pressure. How does it ? When there is no more room in the bellows for the water to move sidewise, it must press upward, if the water is continually running in, because it can go no other way. 9 130 HYDROSTATIC BELLOWS. How could you let the water out of your bel- lows ? By making a hole at the bottom of the tube. How can you show the pressure of AIR with the same instrument or bellows ? Two men may stanti on it, and one of them may blow hard into the tube, instead of pour- ing in water, and they will both be lifted up. How can they keep the air in the tube and bellows from coming out ? By putting the finger tightly down upon the top of the tube. If you fill a vial almost full of water and cork it, and then turn it up and down, what will you see moving up and down along the side of the vial ? A bubble of air. If you lay it on an inclined plane, where will the bubble be ? Near the upper end of the vial. Where will it be if you lay it on a level table ? Exactly in the middle of the vial. SPIRIT-LEVEL. 131 How can you tell whether a table is level, or inclined ? By laying the vial on it, and looking at the bubble, to see if it is in the middle or near one end. What useful instrument is made somewhat in this way ? A spirit-level. What is a spirit-level ? It is a glass tube, nearly full of colored spirit, and is fitted into a brass case, in such a way that the bubble of air can be seen. If you wish to find whether the floor is level or inclined, how must you use this instrument ? I must place it on the floor, and see wheth- er the bubble of air is in the middle of the tube. For what purpose is the spirit-level often used ? It is used in making roads and canals. What are canals ? They are large, long ditches, filled with water, that go from one town to another. 132 CANALS. AQUEDUCTS. Why are canals made ? Because there are no rivers in just the places where men want them, and so they make rivers for themselves, for boats to sail upon. Where do they get the water to Jill their ca- nals ? From the rivers near them. What is done when a canal must go across a river ? They make tight bridges, which carry the water in the canal safely over the river. CANALS. AQUEDUCTS. 133 What are such bridges called ? Aqueduct bridges. What is the meaning of AQUEDUCT ? Aqua means water, and duct means leader. Then what do you mean by AQUEDUCT ? A water-leader. Chmttutlj, F / should take a glass lube, open at both ends, and put it into a, bowl of water, and then press down all the water around the tube, what would it do? The water would rise up into the tube. What would make it rise into the tube ? Your hands would press down the water around the tube, and the water could not help rising in the tube What is mercury ? It is a liquid metal, that looks like melted silver. What is mercury sometimes called ? QUICKSILVER. BAROMETER. 135 Quicksilver, or liquid silver. If I should put quicksilver or mercury into the bowl, instead of the water, and then press it down, would it rise in the tube ? It would ; but not as high as the water rose, unless you pressed upon it more than you did upon the water. Why would it not ? Because mercury is so much heavier than water. If I could take all the air out of the tube, and stop the upper end, and put the other end into the water, would the water rise in the tube, if I did not touch it ? It would. What would make it rise ? The air around the tube. How could the air make the water rise in the tube ? By pressing down upon the water in the bowl. What does this prove ? 136 BAROMETER. It proves that the air has weight. BAROMETER. What is the name of the instrument, made of such a tube and bowl of mercury ? Barometer. What is the meaning of the word BA- ROMETER? It means a measurer of weight. When the air is so heavy as to press up the mercury high into the tube, what weather do we have ? Clear, pleasant weather. Why is the weather pleasant then ? Because the air is heavy enough to hold up the clouds, and prevent them from falling down. How can you tell when the air grows lighter ? The mercury sinks in the tube. What makes it sink ? The air does not press so heavily upon the mercury in the bowl, and so the mercury can not rise as high in the tube. What weather do we have when the mercu- ry sinks in the tube ? 138 BAROMETER GOOD EFFECTS. Stormy weather. Why do we have stormy weather ? Because the air is not heavy enough to hold up the clouds, and so they fall down in rain. Then what good does a barometer do us ? It shows us what weather to expect. Who always need barometers ? Captains of ships, at sea, Why do they need them ? Because a sudden storm would destroy a ship sooner than it would a house. How would a barometer prevent a ship from being destroyed ? The captain could see the mercury sinking in the tube, and would immediately prepare the ship for the storm, and thus save it. Can you relate a story of a captain's sav- ing his ship, because he had a barometer ? Dr. Arnot gives the account. He was in the ship at the time. He says they were in the southern hemisphere. The sun had just BAROMETER. GOOD EFFECTS. 139 mildly set, closing a beautiful afternoon. The evening amusements were going on as usual, when suddenly the captain's orders came to prepare with all haste for a storrn. The mer- cury in the barometer had begun to fall with awful rapidity. As yet, the oldest sailors could see nothing like a storm in the sky, and were surprised at the greatness and hurry of the preparations. But before every thing was quite ready, a hurricane came on them, more dreadful than the oldest of the sailors had ever known. Nothing could resist its power. The sails were torn to tatters, the masts in- jured, and, at one time, the whole rigging was near being destroyed. So loudly, for a few hours, did the hurricane roar above, the waves around, and the dreadful thunder peal, that no human voice could be heard ; even the speaking-trumpet sounded in vain. On that awful night, if it had not been for the little tube of mercury which gave the warning, neither the strength of the noble 140 BAROMETER. GOOD EFFECTS. ship, nor the skill and activity of her com- mander, could have saved one man to tell the tale. _~^ ^^~~~ gup ow Ugh above the earth does the air extend ? Forty-five miles. Then how many miles of air press down upon the mercury in the bowl? Forty-five miles of air. If the tube was as large as a pump, and the bowl as large as a cistern, would water rise in the tube ? It would. What would make it rise ? The weight of the air pressing upo water around it, What is necessary to the making of a pump / A large tube, with the upper end closed. 142 PUMPS. If there was AIR in the pump, would the water rise in it ? It would not. Why would it not ? Because the air and water could not be in the same place at the same time. If the top of the pump was taken off, would the water rise in it then ? It would not. Why would it not ? Because the air above the tube could then press down through the tube, and keep the water from rising. How could the air be taken out of the pump. By making a stopper just as large as the hole through the pump, that can slide up arid down in it What is the stopper in a pump called ? It is called the piston. It has a hole through it. PUMPS. 143 What is there on the top of this stopper or piston ? Just over the hole in the piston, there is a little leather cover, fastened so as to open and shut like a little door on a hinge. What is this COVER called ? It is called a valve, or little door. WJiere is there also another valve ? In the lower part of the pump. You said the air could be taken out of the pump by such a piston as you have described ; how could this be done? When I press the piston down toward the water, the air underneath lifts up the cover or valve in it, and escapes through the hole. What will then be below the piston? Nothing but water. If you now raise the piston, what will the water do? It will open the lower valve and rise as fast as the piston rises. What will make the water rise ? 144 PUMPS. The air pressing upon the water in the cistern, outside of the pump. When the piston is pressed down the second time, what will take place ? As it is pressed down, the water under it closes the lower valve, and forces up the little valve of the piston, and when it is open, the piston can sink down through the water. What will take place when the piston is drawn up again ? The water above the piston will press upon the little valve and close it, so that the water can not pass back through the piston again. What becomes of the water above the piston then ? As the piston rises, it lifts up this water, and throws it from the pump. How could you raise as much water as you wish ? By moving the piston down and up several times. How could you press down the pisto?i ? PUMPS. 145 By having a long pole fastened to it, with a handle at the top of it. What is the long pole called? The pump-handle. Here is a picture of a pump. How high will water rise in a pump, where there is no air ? Thirty-four feet. 10 146 PUMPS. Why will it rise no higher ? Because the air does riot press heavily enough upon the water in the cistern, to raise the Water any higher in the pump. What does this prove? It proves that thirty-four feet of water weighs just as much as forty-five miles of air does. Then which is the heaviest, air or water? Water. Would the mercury rise thirty-four feet in a tube? It would not. What does that prove ? That mercury is heavier than water. =fS= _ -, OW things which they call SUCKERS? v They take a round | piece of wet leather, and fasten a string in the center of it. How do they use it ? They press the leather very closely to the stone which they wish to lift, and then, when they lift up the leather with the string, the stone comes up with it. What makes the stone rise too ? When the string pulls up the leather, it stretches the leather, because it is wet, so that nothing but its edges touch the stone. 148 SUCTION. Then what is between the leather and the stone ? Nothing, not even air. How do you know there is no air under the leather ? Because the edges of the leather are fixed so tightly to the stone, that no air could get under it. Then what keeps the stone and leather so tightly together? The pressure of the air. What does this prove ? That air has weight. SUCTION. 149 What if the edge should be lifted up on one side ? The air would get between the leather and the stone Could you lift the stone with the sucker then ? I could not. Why could you not ? Because the air under the sucker would press it up, while the air above was pressing down. Then when you wish to raise any thing with a sucker, may you have any air between the sucker and the weight? I must not. How can a fly walk upon a window-glass? Its feet are much like suckers, and are kept upon the glass by the pressure of the air. How can they take them up from the glass, so as to walk as .fast as they do? God has given them the power of letting the air under their feet very quickly, when- ever they wish to step. 150 FLIES. LIZZARD. WALRUS. Are there any other animals that walk over smooth surfaces by means of such feet ? The lizzard, that lives in the island of Java, walks up a smooth wall in the same way, to catch flies ; and the large walrus walks upon ice easily, because his hind feet are shaped like a sucker. Have any kinds of fishes this contrivance ? One kind of fish has a set of suckers upon its head, that enables it to fasten itself to rocks, or to any thing it chooses. If you should cork an empty bottle, and let it down deep into the sea, what would happen to the bottle ? It would be crushed. What would crush it? The water pressing all around it would crush it in. What does this prove ? It proves that the pressure of water is greater than the pressure of the air. If you Jill the bottle with water, and, cork it> SUCTION. and then let it down into the sea, will it be crushed ? It will not. Why will it not? Because the water in the bottle presses out- ward so strongly as to prevent the pressure of the water around the bottle crushing it. Jf you should take a tight barrel, filled with water, and make a hole on the under side for the water to run out, would it flow ? It would not. Why would it not ? Because there would be nothing to press it down. How could you make the water run ? By making another hole in the upper side of the barrel. What good would that do ? It would make a place for the air above the barrel to press down upon the water in the barrel. Then when you wish to have the fluid in the 152 DIVING-BELLS. barrel run out at one end, what must you always do? I must take out the bung or stopper at the top, to let the air come into the barrel. What contrivance have people for going safe- ly to the bottom of the sea ? They can go in Diving-Bells. What are they ? They are shaped like a bell, and are large enough for one or two persons to sit in them. How is the water kept out of them? DIVING-BELLS. 153 They are let down into the water in such a way that the air in them can not escape ; and thus the air prevents the water from rising into them. How can you explain this ? If I put a tumbler into water, with the up- per side down, I can not fill it, because the air in it will not allow the water to come up into it too. How can the persons in the diving-bell breathe 1 A long, flexible tube goes from the inside of the bell up through the water, and the air is passed down to the men through it. What other contrivance has been made, for the same purpose ? Instead of a bell, a tight cover has been made for the head, which has an air-tube fixed to it. A man can fasten this cover upon his head, and put on a water-proof dress, and then go safely down to find pearls, or wrecks of ships, at the bottom of the sea. F you throw a stone into the water, what will the water do ? It will move in little waves, shaped like cir- cles, and these circles will grow larger and larger. When the steeple-clock strikes, what does it cause the air to do ? It makes the air around it move in circular waves, just as the water does when a stone is thrown into it. When one of the circles reaches your ear, what do you say ? I say that I hear the clock striking. Then what is sound ? Sound is the effect of air coming against the ear. SOUND. 155 What are these circular motions, or waves of the air, called? They are called vibrations of the air What is necessary then to make a sound ? Something that will vibrate. How is it known that sound is conveyed by means of air ? A bell has been rung in a glass vessel, when the air was taken out of it, and it made no sound. If a cannon should be fired several miles off, would you hear it the moment it was fired ? I should not. Why would you not 1 Because it takes some time for the waves made by the cannon to reach my ears. What brings the sound of the cannon to your ears ? The air. Then what may we call the air ? A conductor of sound. 156 SOUND. AIR. BELL. Why do we hear a bell ring more distinctly, when the wind blows toward us from the bell? Because it brings more waves of air to our ears, than would reach us, if the wind did not blow that way. When the wind blows in a different direction, how does the bell sound ? Very faint, and sometimes we can not hear it at all. Why is the sound so faint ? Because the wind blows almost all the waves of air away from our ears. If you strike two stones together in water, can you hear the sound as plainly as you can in the air? I can, if my head is under the water. What does this prove ? It proves that water is a good conductor of sound. Which is the best conductor of sound, water or air ? Water. SOUND. 157 How can this be proved ? If a bell should be rung in water by one person, and another person at a distance should put his head under the water, it would sound much louder than if the bell arid the person were out of the water. If you lay your ear upon one end of the ta- ble, and I scratch the other end of the table with a pin, will you hear it ? Yes ; and it will sound very loud. What does this prove ? It proves that wood is a good conductor of sound. Why do animals seem to know an earth- quake is going to take place sooner than men do? Their heads are so near the ground that they hear the rumbling sound first. What does this prove ? It proves that the earth is a good conductor of sound. Can you repeat a story that shows what good 158 SOUND. EARTH. it has done to know that the earth is a good conductor of sound ? Many years ago, there was a war in Greece. The Greeks fought against the Turks, be- cause the Turks had got their lands away from them, and treated them very cruelly. In one of the Greek cities, there was a strong tower. The name of the city \vas Misso- longhi. A great many Greeks had fled to this tower, to get away from the Turks. The Turks came, and tried to destroy the tower. It had a great quantity of powder in the cel- lar, for the Greek soldiers to use. After try- ing a good while to destroy it, the Turks went away, as if they were not going to try any more. They began to dig a hole at some distance from the tower. The Greeks did not know what it was for ; but soon one Greek began to think that the Turks were digging a hole under ground, to reach the cellar of the tower. He thought that they would lay tow all along, (from the powder in the cellar to CONDUCTORS OF SOUND. 159 the beginning of the hole,) and then set fire to the tow. This would burn till the fire got to the powder in the cellar, and then that would take fire and blow up the tower, and all the people in it. What did the Greek do ? He piled up some stones in the middle of the cellar, or magazine, as a cellar of powder is called, and put four smaller stones very loose- ly upon the top. Then he watched those four stones till he saw them shake. As soon as they began to shake, he put his ear down to the earth, and could hear which way the sound came from. As soon as he found out which way the sound came from, he began to dig down, and soon came to the tow that was laid there, all ready to be set on fire. This he destroyed. When the Turks had set the further end on fire, they waited at a distance to see the tower blow up. When they found that it did not blow up, they began to dig somewhere else. 160 CONDUCTORS OF SOUND. What did the Greek do then ? He kept watching the stones, and soon saw them shake again. Then he put his ear down and heard the noise, and dug again till he, came to another train of tow, and destroyed that. Did the Turks try again ? They did, several times ; but at last they began to think that the Greeks knew what they were doing, and so they gave over trying to blow up the tower. ow fast does sound pass through the air ? One mile in about five seconds of time. Then, if you should see the flash of a cannon, and could count thirty seconds be- fore you hear the first sound, how far off should you say the cannon was ? It would be six miles off. How could you tell ? If it goes one mile in five seconds, it would go six miles in thirty seconds, because there are six times five in thirty. If it should lighten, and you should not hear it thunder till you had counted fifteen seconds, 162 REFLECTION OF SOUND. how far off should you say the thunder-cloud was? Three miles off. How would you find out that ? There are three times five seconds in fif- teen seconds, and if five seconds would bring the sound one mile, fifteen seconds would bring the sound three times as far, which would make three miles. If you speak very loud, what will the air around you do ? It will begin to move or vibrate in circles, that will spread further and further. If these circles spread till they strike against a high rock, what will happen to them ? The rock will reflect or send them back, just as it would a ball, if you threw one against it If the circles made by the reflection of the rock should come back to the ear, what would you say ? I should say I heard the echo of my voice. ECHOES. 163 Then what is an ECHO ? An echo is sound sent back again. What besides rocks will echo ? Hills, buildings, and walls of rooms, if they are near enough and not too near. How near must they be, in order to make an echo, when you speak very loud ? So near that the circles made by my voice can reach them, and that they can send the circles back to me. If the rock should also send its circles to an- other rock, that would send them back to your ear, what would you hear ? I should hear two echoes. How would it be, if several rocks or surfaces sent back the sound at different instants ? I should hear several echoes. Are. there any places where several echoes can be heard ? There are many in the world. Can you mention one in the United States ? At Lake George there is a place where a 16-1 ECHOES. person can stand, and call out very loudly, and he will hear several echoes. What curious echo is there in England ? At Woodstock, there is an echo that will repeat seventeen syllables , and, on the north side of the church at Sussex the echo will repeat twenty-one syllables. What one still more wonderful can you mention ? In Italy, near the city of Milan, there are two walls of a building that face each other, and a person, standing at a window between them, can hear the echo repeat one word more than forty times. How is it when a pistol is fired there ? The echo repeats the sound sixty times. What can you say of the Whispering Gallery of St. Paul's Church, in London ? If a person whispers very softly close to the wall on one side of the gallery, it will be echoed so that, if another person puts his ear close to the wall on the other side of EOLIAN HARP. GIANT'S HARP. 165 the gallery, be can hear every word dis- tinctly. What is an Eolian Harp ? A musical instrument made with strings. Can you describe it ? Strings or wires are stretched very tightly from one fastening to another, and placed where the wind can blow directly upon them. What does the wind do to the strings ? It makes them strike against the air, and, when the circles made by them reach your ears, you hear very sweet sounds. What very large one TV as made in Milan, many years ago ? Gattoni stretched seven strong iron wires from the top of a tower fifty feet high to the house of Signer Mascati. What was it called ? The Giant's Harp. Why was it called the Giant's Harp ? Because, when the wind blew, it sent forth 166 GIANT'S HARP. such lengthened peals of music : now it was a loud chorus, and then it died away in soft murmurings. In a storm it was heard several miles. HEN children carry fruit along the streets in cities, to sell, why do they turn toward the houses they pass, and put their hand up to one side of their mouths, when they scream out " Strawberries ? " 168 PROJECTION OF SOUND. So as to make the sound of their voices go into the windows, instead of spreading out and being- lost in the noise of the o streets. When a boy is calling to another, who is at a distance, what does he often do ? He puts both hands around his mouth, like a tube, and then calls. Wlnj does he put his hands around his mouth ? SPEAKING-TRUMPETS. 169 They keep the sound from spreading out, and thus make it go straighter to the other boy's ear. If the oilier boy hears the sound, and turns around to know what is wanted, what will he do? He will probably put one hand to his ear, to listen. Why will he do so ? So to catch more of the sound of his friend's voice. What do firemen and sea-captains use, instead of their hands, to make their orders heard in a great noise ? They use speaking-trumpets. 170 EAR-TRUMPETS. What contrivance have people for hearing instead of putting the hand to the ear ? They have ear-trumpets, or tubes. How can deaf people hear the conversation of their friends ? They have a long, flexible tube of India- rubber, with a small ivory opening at one end, to go into the ear, and at the other end is a larger opening made of ivory. How is it used ? If I wish to speak to the deaf person, he puts the small end to his ear, and I take the other end of the tube, and speak into it. Why will this help him to hear you ? SPEAKING-TUBES. 171 The sound goes directly from mj lips, through the tube, into his ear. How is it when you have no tube ? The sound goes everyway when it leaves my mouth, and so but little could go into his ear. What contrivance is made in houses, by which people in the upper part can easily talk with those in the rooms below ? Tubes are put into the walls, with openings from them into the rooms, upstairs and below. How are they used? If a person in the upper room speaks into the tube opening there, the other in the room below hears, and goes to the opening in his own room, and puts his ear to it to listen, and then speaks back through the tube. Must they talk very loud ? They need only speak as if they were in the same room. Why? Because the sound is kept in the tube till it gets to the othe opening. esson NTO how many colors may light he separated ? Light may be sepa- rated into seven colors. What are the names of these colors 1 Violet, indigo, blue, green, yel- low, orange, red. When light shines upon a sheet of paper, how can you see the paper? By the light which the paper reflects or throws back to my eyes. Would the paper reflect ALL the light that shines upon it ? If it was white paper, it would. How do you know that WHITE paper reflects ALL the light that falls upon it? COLORS. 173 Because it takes all the seven colors to make white light, and the paper looks white, which it could not do if it did not reflect all the sev- en colors. How do you know that it takes all the seven colors to make white ? Because, if you separate a ray of white light by a prism, it will be changed into just seven colors, and no more ; and if you bring all these seven colors together again, they will form a ray of white light. Do all bodies reflect all these colors ? They do not ; some reflect one color, and some another. What becomes of those colors which the body does not reflect ? That body absorbs them. What do you mean by a body's ABSORBING colors 1 It seems to take them into itself, so that we can not see them. If a "body should absorb all the col- 174 COLORS. ors, and reflect none, what color would it have ? It would not have any color. Then what should we call it? We should call it a black body. Then is black a real COLOR ? It is not. Then, when we say a body is black, what do we mean? We mean that the body has no color. And, when we say a body is WHITE, what do we mean ? That it has all the seven colors. Jf it absorbs all the colors but the red, and reflects the RED, of what color will the body be? It will be a red body. What color shall we call it, if it reflects the green, and absorbs all the rest ? We shall call it a green body. How can you tell which color a body reflects, and which it absorbs ? It will be of the color it reflects, and COI.OKS. we shall know it absorbs all the colors but thai. Then how do we see any object? Bv the color it reflects to our eye. \Vhat is the reflection of //( but a c-rta..ity of imj)rovem..:)t. I-'rom the Connecticut Observer. This liti'j vl.i.': i an admirable counterpart to t', a tir f that wn-^ .nd which t hibited the tact of the writer for addrewin? youthf- 1 m?r nt ) " fe tt C8n he !nade who, io the -rarly developinciiU ,.| ihoufh\7 wiin'to'rnquire | tnmgs, and are /- -i'l u f curiosity vith reg. -<\ to the objecta y!e . it sLo ' brightly p - '.hat mi modes of explanation are very judi, ,>us TI the chain of consecutive ret oning clenr' ter of rejoicing to all parents and teacHoio writer, are devoting their powers to such wcj liternture of the country. From the Fall Rh fr J,fcn , These less, ns are admirably adapted to the capacit:? of chil<-;cn. P.VR MUhe I, lit SU '- inj, o'ho:e ito the tense of "; ; the and mat- SitD. d. r ^e th Iu the -rthe i From the Jfew York Plaindcalcr. 'Inis book i obv'ously the production of one who undfrstands the wa u ar , ,apa cl t,es of yen- young students, and what is more r tti e, understaJ how* Lceojnmodare I rself to their immature intellect*