OBJECT LESSONS ELEMENTARY SCIENCE OBJECT LESSONS IN ELEMENTABY SCIENCE FOLLOWING THE SCHEME ISSUED BY THE LONDON SCHOOL BOARD BY VINCENT T. MUECHE HEADMASTER OF BOUNDARY LANE BOARD SCHOOL, CAMBERWELI. AUTHOR OF BLACKIE'S 'PHYSIOLOGY,' 'BOTANY,' ETC. VOL. II MACMILLAN & CO. BEDFORD STREET, STRAND, LONDON AND NEW YORK 1895 All rigjits reserved First Edition July 1894 Reprinted with corrections October 1894. Reprinted 1895 PREFACE SOME years ago the London School Board issued a Scheme of Object Teaching in Elementary Science. This Scheme was at once adopted by the compiler of these Lessons for use in his own school. He started by writing complete Notes of the Lessons, based on the Scheme, for each section of the school ; and has exercised much care and thought in getting together a museum of suitable objects for illustrating the teaching. The result has been a marked success the teachers as well as the children deriving pleasure and benefit, and looking forward to the lessons as a welcome break in the monotony of the school routine. H.M. Inspector has always shown his commendation of the work ; and in July last he brought the Right Hon. A. H. D. Acland, the Vice-President of the Council, on a visit to the school for the purpose of witnessing the teaching in this subject. The Vice-President spent about an hour and a half with the various classes, showed great interest in the work, examined the books of written lessons, and himself suggested the advisability of publishing them. Hence they now appear in book form. vi OBJECT LESSONS A special point in the arrangement of the Lessons is that they are all written in full, no single step being left unexplained. The pupil-teachers can therefore be allowed to take their share of the work, to their own benefit and improvement, without loss to the children. The instructions to the teachers are printed in italics, the salient points of the lesson are conspicuously shown in the change of type, and lists of suitable objects for illustrat- ing each lesson are placed at the end of the book. As the books are intended for the teacher and not for the class, there is no need for copious illustration. The plates at the end are intended for reproduction as black- board sketches, and generally for the guidance of the teacher. The teacher will reproduce on the black-board as much as he can of each sketch, according to his individual skill with the chalk. The universal complaint from Inspectors in all parts of the country has been that the so-called " Object Lessons " too often fail in their purpose, because nothing is so con- spicuous as the absence of the objects themselves. The main purpose throughout this course has been never to use a picture where the real object can (with a little trouble) be obtained ; and the Author has found, and still finds, that the teachers as well as the children take a lively interest in adding to the stock of articles in the school museum. The various stages are written up to the possibilities of a school of good repute, well appointed and staffed. In schools not so fortunately placeil, a rearrangement of the PREFACE Vll Standards might be made Standards I. and II. taking the course prescribed here for Standard I., and so on. In smaller schools, and girls' schools, the lessons dealing with Animal and Plant Life alone would make an interesting and useful course; or the lessons on Common Objects (Standards I. -III.) might be followed in the higher Standards by the course in Mechanics, Botany, Zoology, or Chemistry, at the teacher's pleasure. The complete course covers almost the entire ground of alternative subjects prescribed by the Code 0/1894. The Author begs to acknowledge his indebtedness to Mr. Rick's admirable book, Object Lessons and How to Teach Them; also to The Chemistry of Common Life; Animal Products; Strength of Materials and Structures; Dictionary of Manufactures ; and for trade statistics to the researches of friends. 2090909 SCHEMES OF LESSONS STANDARD III I. LESSONS FROM PHYSICS 1. Liquids may be made to flow in a stream or in drops. Cannot be grasped by the hand. Cannot be made to form a heap. Have no shapes of their own ; but take the shapes of the vessels in which they are placed. Water. Its special properties, as shown by observation and experiment. Ice and steam how formed. Uses of water depend- ent on its solvent power. Spring-water, rain-water, sea-water. Compare as to properties. Mercury. A liquid metaL Note its chief properties and uses. Alcohol. Its chief properties. Its use in the spirit-lamp, and as a solvent. Instance camphor. Paraffin-oil. Its chief properties. Its source. Its uses for lighting and heating. Danger in its use. How to avoid the danger. 2. Gases. How they differ from liquids. Air. A substance, invisible, occupies space, has weight, presses equally in all directions. Illustrate by experiments with the air-pump. Coal-gas. Its properties and manufacture, illustrated by experiment. Fire-damp. Coal-gas in mines. Choke-damp. Carbonic acid gas. Balloons. How they rise. Carbonic acid gas. How made; its properties; its presence in the air; its dangers. Animals exhale it, plants inhale it. x OBJECT LESSONS Show how it can be poured from one vessel to another, and how it extinguishes a flame. Water-gas, or vapour. Always present in the air. Animals and plants exhale it. Illustrate by passing the breath through a tube into a clean glass bottle ; also by enclosing a small branch with its leaves in u bottle. Evaporation. II. LESSONS FROM BOTANY 1. Parts of a plant. General description, with uses of the various organs. 2. Parts of a flower. The calyx, sepals, corolla, petals, stamens, anthers, pollen, pistil, ovary, style, stigma. Special function of the flowers. 3. Seeds and seedlings. Illustrate by the growth of the scarlet-runner and the wheat-plant from the seeds. Plants with two seed-leaves, plants with one seed-leaf. 4. Plant fibres. Obtained from the inner bark of stems. Illustrate with bast, flax, hemp, and jute. Preparation from the bark. Compare these fibres as to special properties and special uses in the manufacture of textile fabrics. Specimens raw and prepared, and manufactured articles to be placed in the hands of the children for examination and comparison. III. LESSONS FROM ZOOLOGY 1. A bird. The covering of feathers. General structure of feathers, quill, shaft, web ; properties and uses of each. Wings instead of fore-legs. Hollow bones. Why 1 Beak and tongue. How the bird takes its food. The legs and claws. How some birds perch, and how some run, or swim. Take the duck as an example of the class. 2. A reptile. The common snake as a type of this class of animals. Adaptation of structure to habit. Elongated form for creeping. Teeth for holding, not for chewing. Arrangement for enlarging the cavity of the mouth for swallowing large prey. Ball-and-socket joint backbone and ribs its special purposes. 3. A frog. Curious life-history. The tadpole its general structure and arrangement for feeding, for breathing, and for SCHEMES OF LESSONS xi locomotion. The frog ; its eyes, skin, teeth, legs, and feet ; absence of ribs ; how it breathes ; its tongue as an instrument for capturing prey. Comparison of tadpole and frog as to struc- ture and habit. Compare with toad. Frogs and toads are classed by themselves as batrachians, viz. frog-like animals. 4. A fish. The herring as a type. Shape for cleaving the water ; illustrate with wedges. The covering of scales, and the oil for lubricating. Horny mouth ; no tongue. Gills and their use. How fishes move through the water ; illustrate with an oar. Compare with other common fish. 5. An insect. Structure of insects generally. Division into three parts. Peculiar structure of mouth, wings, and legs. How insects breathe. Take the bee, house-fly, butter-fly, silk-worm, beetle, and cockroach as examples. 6. A spider. General structure, and how it differs from an insect. Spider-silk, and the various uses to which it is put by the spiders. STANDARD IV I. LESSONS FROM MECHANICS 1. Extreme divisibility of matter. Molecules. Cohesion of molecules. Explanation of three conditions of matter solid, liquid, gas. Adhesion ; capillary attraction. 2. Solids. Properties of solids explained hardness, weight, etc. 3. Liquids. Why the surface of a liquid at rest is always level. Explanation of pressure in liquids. Pressure increases with depth. At the same depth the pressure is equal in all directions. Liquids transmit pressure. Buoyancy of liquids. Floating and submerged bodies. Solid bodies weigh less in water than in air. 4. The atmosphere weight of. Pressure equal in all directions. Pressure varies with height above the sea-level. The weight of the atmosphere varies. The principle of the barometer. The boy's sucker, the syringe, suction-pump, and air-pump to be explained and illustrated. xii OBJECT LESSONS II. LESSONS FROM HEAT Effect of heat on bodies generally. Expansion and contraction of solids. Application in artisans' work. Liquefaction of solids by heat. Expansion and contrac- tion of liquids. Eemarkable exception in the case of water. How we measure temperature. Thermometers. III. LESSONS FROM BOTANY (Bors ONLY) 1. Structure of the endogenous stem. The oak and the fir how they differ. Hard woods, soft wood, heart- wood, sap-wood, direction of the grain and the medullary rays (silver grain). Seasoning of wood. Direction of shrinkage. Preservation of wood. 2. Woods used as timber. Enumerate their special properties and uses. Sources of supply. IIlA. LESSONS FROM PHYSIOLOGY (BOYS OR GIRLS) 1. General structure of the human body. The bones and joints, skin, muscles, nerves. 2. Respiration, circulation, digestion. General structure of the organs concerned in each. 3. The atmosphere oxygen, nitrogen, carbonic acid, water, vapour, ventilation. 4. Water. Oxygen and hydrogen. Pure and impure water. 5. Carbon and carbonic acid. IV. LESSONS FROM ZOOLOGY (BOYS OR GIRLS) 1. Division into vertebrate and invertebrate. 2. Division of vertebrates into mammals, birds, reptiles, batrachia, and fishes. Characteristic differences in structure in relation to habit. The form of the body, the covering of the body, the limbs and how used, the mouth, teeth, and tongue. 3. Position of the chief internal organs ; their uses and char- acteristic differences. One animal from each class may be selected as a type. CONTENTS STANDARD III LESSON PAGE LESSONS FROM PHYSICS LIQUIDS .... 3-29 1. WATER A LIQUID ..... 3 2. WATER AS A SOLVENT ..... 7 i/~ 3. WATER ix OTHER FORMS . . . .10 ;/" 4. WATER IN OTHER FORMS . . .14 5. SOLID WATER . . . . . .17 6. MERCURY ITS PROPERTIES . . . .21 7. MERCURY ....... 23 8. ALCOHOL . ...... 25 9. ALCOHOL . . . . . . .27 GASES ........ 30-51 /" 10. AIR . . . . . . . 30 11. AIR continued . . . , . .32 12. GASES ..... . 34 13. COAL-GAS ....... 87 14. COAL-GAS continued . . .39 15. OTHER PRODUCTS OF COAL . e . .41 16. PARAFFIN OIL . . . . 43 17. CARBONIC ACID GAS . . . .46 18. CARBONIC ACID GAS continued . . 49 xiv OBJECT LESSONS LESSON PAGE LESSONS FROM BOTANY . 51-76 r 19. PARTS OF A PLANT . 51 /" 20. THE WORK OF THE ORGANS . . . 53 /" 21. PARTS OF A FLOWER . . 55 22. THE FLOWER AND ITS WORK . . . .58 ^23. SEEDS AND SEEDLINGS DICOTYLEDONS . GO ^ 24. How SEEDS GROW ... 62 I* 25. SEEDS AND SEEDLINGS MONOCOTYLEDONS 64 26. THE BARK . . .68 27. KINDS OF BASS . . 70 28. FLAX . 72 29. LINEN-MAKING , . 74 LESSONS FROM ZOOLOGY . . . 76-122 ^ 30. BIRDS AND THEIR COVERING . . . '7<; 31. A FEATHER . 73 32. BIRDS .... 81 \f 33. CLASSES OF BIRDS ... 83 34. BIRDS LEGS AND FEET . 86 35. REPTILES . . 90 36. KINDS OF SNAKKS . 94 v 37. THE FROG . . 97 / 38. THE FROG continued . 100 S 39. THE FROG ITS LIFE-HISTORY .... 102 / 40. A FISH . . . 10g jr 41. A FISH cmUinui'il. .... 109 42. AN INSECT . . . . .112 / 43. AN INSECT continued . . . . .116 Y 44. A SPIDER .... MS j/ 45. THE SPIDER'S WEB . . . . .120 CONTENTS xv STANDARD IV LESSON PAGE LESSONS FROM MECHANICS .... 125-169 1. MATTER ....... 125 2. CAPILLARY ATTRACTION . . . . .129 3. PROPERTIES OF SOLIDS ..... 130 4. AVEIGHT . . . . . .133 f>. LIQUIDS . . . . . . .137 6. PRESSURE OF LIQUIDS ..... 140 7. PRESSURE OF LIQUIDS continued . . . 142 8. BUOYANCY OF LIQUIDS . . . . . 144 9. PRESSURE OF THE ATMOSPHERE . , . .147 10. WEIGHT OF THK ATMOSPHERE .... 151 1J.. THE BAROMETER . ... 154 12. THE SYRINGE . . 159 13. THE SUCTION-PUMP . . . .161 14. OTHER PUMPS ...... 164 15. THE AIR-PUMP . . . . . .166 LESSONS ON HEAT ..... 169-183 16. How HEAT AFFECTS DIFFERENT SUBSTANCES . . 169 17. EXPANSION AND CONTRACTION . . . 172 18. THE THERMOMETER ..... 174 19. HOW TO MAKE A THEUMOMETER . .176 20. THERMOMETERS . . . 179 21. ICE . . . 181 LESSONS FROM BOTANY ..... 183-198 22. THE WOODY STEMS OF PLANTS . . . .183 23. THE WOOD OF THE EXOGENOUS STEM . . . 186 24. THE OAK AND THE FIR . . . .189 25. TIMBER .... . 192 26. TIMBER ITS USES 195 xvi OBJECT LESSONS BOYS OR GIRLS I^SSON PAGE 27. THE ATMOSPHERE WHAT IT is . . . . 199 28. MORE ABOUT THE ATMOSPHERE .... 201 29. WATER ITS COMPOSITION .... 203 GENERAL STRUCTURE OF THE HITMAN BODY . . 206-229 30. THE BONY SKELETON . . . . .206 31. THE JOINTS . . . . . .211 32. MUSCLES, NERVES, AND SKIN . . . .215 33. CIRCULATION OF THE BLOOD .... 219 34. DIGESTION . ..... 223 35. RESPIRATION ...... 226 LESSONS FROM ZOOLOGY ..... 230-269 36. THE ANIMAL KINGDOM . . . . .230 37. NATURE OF THE BACKBONE .... 232 38. VERTEBRATES ...... 234 39. THE INVERTEBRATES ..... 237 40. CLASSIFICATION OF INVERTEBRATES . . . 239 41. MAMMALS ....... 241 42. MAMMALS continued ..... 244 43. BIRDS . . . . . . .246 44. BIRDS continued ...... 249 45. REPTILES, BATRACHIA, FISHES .... 251 46. STRUCTURE AND HABITS COMPARED . . . 255 / 47. THE COVERING OF ANIMALS .... 258 48. THE MOUTHS OF ANIMALS .... 262 49. THE INTERNAL ORGANS ..... 265 OBJECTS AND OTHER ILLUSTRATIONS REQUIRED . . 271 STANDARD III VOL. II STANDAKD III LESSONS FKOM PHYSICS LIQUIDS Lesson I WATER A LIQUID I. INTRODUCTION REFER to the early lessons on water, and lead the class to tell why they learned to call water a liquid, comparing it with such objects as a stone, a piece of wood, a sponge, some flour, etc. When we put the water into various vessels, what happened 1 It spread itself out each time so as to fill every corner of the vessel ; it took the shape of the vessel. What do you remember about the top of the water ? It never stands up in a heap, but always keeps a level surface. Suppose I dip my hand into this basin, to give you a handful of water. Can I do it 1 No. I could do it with a basin of flour, sugar, raisins, pease, but I cannot take up or grasp a handful of water. Why is this 1 Because the little particles of which the water is made up do not hold firmly together as the particles of a solid do. You remember we emptied all the water out of a basin by dipping a brush into it. What happened when I shook the brush ] The water fell away in drops. 4 OBJECT LESSONS STAND, in What afterwards became of these drops ? They ran together again and formed a stream which flowed away along the table. So, then, it was all these properties in water which led us to call it a liquid : 1. It has no shape of its own, but always takes the shape of the vessel which holds it. 2. It cannot stand in a heap, but always keeps a level surface. 3. It cannot be grasped by the hand. 4. It may be made to flow in (streams or drops. Lead the dass to tell that all substances which possess these properties, as well as water, are liquids. Let them enumerate some of those which have been dealt with in former lessons. II. FURTHER PROPERTIES OF WATER Let us next examine this glass of water, and try and learn something more about its other properties. 1. By the sense of sight. Set the glass of water side by side with a glass of milk ; some red, black, and blue ink ; or any other coloured liquids ready to hand. Lead the dass to tell that water has no colour at all. It is not white; milk is white. It is colourless. When I hold this ball behind it I can see the ball through the water. What do we say, therefore, about the water l \ It is transparent. 2. By the sense of taste. Let the children taste the milk, some vinegar, some tea or coffee, some dissolved sugar, salt, or any other liquid ready to hand. Each of these has its own particular taste or flavour. Now let them test the water in the same way. Lead them to explain that water has no taste or flavour of its own. It is tasteless. 3. By the sense of smell. Proceed in the same way by letting the children smell various liquids. They could distinguish them with their eyes shut. Each has it own special odour. LES. i WATER A LIQUID 5 Now let them smell the water. What do they notice? Water has no odour of its own. It is inodorous. Explain the meaning of this long word. 4. By experiment. On the day preceding the lesson place a saucer full of water in a cupboard, side by side with a vessel containing some substance with a powerful odour common green paint or oil of turpentine will do very well for the purpose. Leave the cupboard shut up close till the lesson commences. Tell the children what you have done. Bring the saucer out and let them smell the water. They will find that the water has the same odour as the substance in the other vessel. How has this come about? The two vessels have merely stood side by side in the cupboard. None of the strong smelling substance was actually put into the water. Tell that little particles of tlie substance have been continually passing off in the form of gas, and that these little particles have been absorbed and sucked up by the water. Water is very absorbent and will suck up and hold In order to make these gases as intelligible as possible, refer to the water passing off in vapour from the evaporating dish, and to the preparation of coal-gas in the clay pipe. Both these are gases. We have spoken of them before. We shall deal more particularly with gases in a later lesson. Water, then, being so absorbent, it is necessary to keep the cisterns which hold the water we want for drinking and for cooking our food as far as possible from bad smells. Explain that all decaying vegetable and animal matters give off bad gases, which will be sure to find their way into the water if it be near. We cannot drink that water without being made very ill. III. SOME OF THE USES OF WATER Show that the uses to which we put water depend upon its peculiar properties. 1 . It is the natural drink. Lead the children to talk of the various kinds of drinks all made of water with the addition of some other substance. But water is letter than all. 6 OBJECT LESSONS STAND, in Which would they rather have when they are faint and thirsty 1 None so delicious and refreshing as water. 2. It is the natural cleanser. Let the children tell of the uses of water in washing our dirty clothes, and cleaning and scrubbing our houses, It is water that carries off all the unwholesome and offensive matter that would soon bring disease. Our bodies too require frequent washing and cleansing all over, if we are to be kept in health. We all have a plentiful supply of water, and soap is cheap. Use it freely and remove all dirt, for dirt is a powerful source of disease ; and the worst enemy of dirt is water. 3. We cook and prepare our food with water. Lead the children to think how largely water enters into the pre- paration of our food, Now water is useful for all these purposes simply because it is colourless, tasteless, and inodorous. Lead up to this, step by step. Imagine water to be red, or blue, or yellmo. What would happen to everything that was put into it 1 Fancy our shirts, collars, handkerchiefs, our floors and tables, all being dyed red because they were washed in red water. Let them think what would happen if water had any flavour or taste of its own, All our food would take the same flavour as the water in which it was cooked. Everything washed in it would smell the same as the water. 4. Animals live in water. Lead tJie class to think of fishes and other animals tJiat live entirely in the water, These animals all require air, without air they would die. How do they get air ? By coming to the surface to breathe ? No, for many of them never come to the surface of the water. There is abundance of air in the water itself. Water is absorbent and is constantly sucking in air over every part LES. ii WATER AS A SOLVENT 7 of its surface. No fish could live in water, unless water were absorbent. Lesson II WATER AS A SOLVENT I. THE SOLVENT POWER OF WATER REFER to some of the earlier lessons on water, and lead the class to describe its action on such substances as salt, soda, sugar, alum, lime, etc. Here I have a piece of coal and a piece of salt. If I put them into water, tell me how they will act. The salt will dissolve in the water, the coal will not. What does that mean ? The water has the power to break up the solid salt into very tiny particles, but it has no such power over the coal. Put the salt and coal into two tumblers of water. What do you mean by the word dissolve ? To dissolve means to loosen or separate. When the solid salt is put into the water, the little particles of which it is composed are at once loosened or separated from each other and spread themselves through the water. See, I can take out the piece of coal just as it was when I put it in. Can I take out the salt ? No. Why not? Because it is broken up into exceedingly small particles and scattered through the water. How could I prove that the salt is there ? By tasting. Can you think of any other way ? What would happen if I boiled the water over the lamp ? The water would all pass away as steam and the solid salt would be left behind. So, then, the salt is in the water, although it has been broken up into such very small particles that we cannot see it. 8 OBJECT LESSONS STAND, m Who knows any other substances that would act in a similar way if put into water ? Sugar, soda, alum, lime, saltpetre. We have a special name for all such substances. What do we call them ? We call them soluble sub- stances. And what do we say about water because it acts in this way on them ? We say that water is a solvent for these substances. II. WHAT BECOMES OF THE SUBSTANCE WHICH is DISSOLVED Sprinkle some salt in the water, stirring carefully with a spoon meanwhile. Show that the salt continues to break up and disappear in the water. It is being dissolved. Lead the class to tell that there will be an end to this soon. Presently the water will refuse to dissolve any more of the salt, and if we continue to pour it into the tumbler we shall see it sink to the bottom as an undissolved, wet, solid mass. But look at the tumbler. Although we have been adding salt all this time, the water seems no higher in the glass than it was at first. See here is another glass, and instead of putting salt into it, I will put small stones. What happens ? The water rises and flows over the top of the tumbler. Why did it not act in the same way when I put the salt in ? Let us see. In our last lesson we learned that water is very absorbent, and absorbs air. We have heard before of absorbent bodies. What kind of bodies can be absorbent ? Porous bodies, i.e. bodies that are full of holes. Name some porous bodies. A sponge and a brick are full of holes, and they are absorbent They absorb water into their pores. Water too is porous, and when any soluble body is placed in water, the tiny dissolved particles, after being broken up and scattered in all directions, fill up the pores in the water itself. LKS. ii WATER AS A SOLVENT 9 Lead the children now to explain why after a time the salt sinks undissolved to the bottom. All the pores in the water have been filled up with the little particles of salt, and the water can hold no more. If, therefore, more salt is added, it cannot be dissolved, and remains a wet, solid mass at the bottom. Water also absorbs air and gases in the same way, by sucking them up into its pores. III. USES OF WATER DEPENDENT ON ITS SOLVENT POWER Refer to the early lessons on plant life. Whence does the plant, get its food ? From the soil in which it grows. The roots which spread through the soil are the feeders. Picture a hot summer day. The plants droop, and even the grass becomes dry and brown. A shower comes. What is the result 1 Plants, grass, all things revive and hold up their heads again. Why is this? Before the rain came the plants were dying of actual starvation. There was plenty of food of exactly the kind they required in the soil close by ; but the food was useless to the plants till it had been dissolved by water. The rain came and dissolved the substances in the soil, and then the little roots were able to suck up these things in the state of solution. Therefore, but for this solvent power of water, no single plant could live and grow. Rain-water. The rain itself would have been of no use unless it had passed into the earth. The rain-water (as we shall soon see) is nearly pure ; it contains no solid substances in solution, and such water could not support the plant. Let us see what becomes of all the rain that falls. Some of it, as we have just seen, sinks into the soil in our fields and gardens and dissolves plant-food for our plants. 10 OBJECT LESSONS STAND, in Some of it is drained off the land, and runs away into the streams and rivers which carry it out to the sea. Tell how the farmer drains his fields with drain-pipes, and why. This water which flows along to the sea in the form of a river is constantly washing the sides and bed through which it flows, and as it flows it dissolves various substances and carries them off in its course. Some of the rain, however, sinks deep into the earth and trickles through rocks of various kinds, dissolving all that is soluble on its way. By and by the same water bubbles up out of the ground again, and forms what we call a spring. This spring- water always contains solid substances in a state of solution. Make the class tell of certain springs which supply strong brine, from which we prepare table-salt. Whence did the water get this dissolved salt 1 . Tell of mineral springs, and why they are so called. Our ordinary spring-water, which is the best for drinking, contains lime in solution. Whence did it obtain this lime ? Tell of the "fur " in tJie tea-kettle, what it is, and how it comes to be found in the bottom of tfie kettle. Illustrate by showing a glass of lime-water. Tell that th{s water contains dissolved lime, although we cannot see it. Breathe into the water through a glass tube, and show the gradual change which takes place. Tell what it is, and why the solid substance now appears in the water. Continue to breathe into the chalky water, and show that it goes clear again. The chalk was insoluble in the pure water, and hence it could be seen. It is soluble in the excess of carbonic acid, and the water becomes clear in consequence. Lesson III WATER IN OTHER FORMS I. STEAM I WANT you to think over our experiment for getting back the salt from the water which held it in solution. LES. in WATER IN OTHER FORMS 11 How did we do it 1 We boiled the solution in a shallow dish over the lamp. What happened then ? The water was driven off in steam, and the dry salt left behind in the dish. Our business then was simply with the salt. I wanted to show you how to recover the solid salt from the water. Now I want to deal with the water itself. Suppose I fill the dish with water from the tap, and set it over the lamp now. What will happen ? All the water will pass away in steam, and the dish will be left dry. What happens if your mother leaves the kettle on the fire ? The water rushes out of the spout of the kettle in steam, and the kettle is left dry. Where else can we see steam ? We can see it as it rushes out of the funnel of a steam-engine. Well, then, this steam is only water in another form. The water has been changed into the new form by heat. Heat breaks up the water into extremely small particles, so small and so light that they are lighter than the air itself. They therefore rise in the air and mingle with it. Call attention to the steam from the tea-kettle and the railway engine as it flies off into the air, But what becomes of it in the air ? The air is very porous, and absorbs these little particles, just as the water in the tumbler absorbed the little particles of salt dissolved in it. II. VAPOUR Think of washing-day at home. Your mother hangs out the wet clothes on the line, and, after a time, takes them in quite dry. What has become of the water 1 Or perhaps there is a heavy shower, and you find the pavements, roads, and everything wet. You go out shortly after and find them dry again. What has become of all this water ? It has dried up. Well, let us see what we mean by saying it has dried up. The water in the wet clothes on the line and the water on the pavements has been broken up into tiny particles 12 OBJECT LESSONS STAND, m not of steam, but of something like steam. We call it vapour. These little particles of water-vapour rise in the air, and are at once sucked up or absorbed into its pores. We say the water has evaporated. We mean that it has changed into vapour. Mother hangs out the wet clothes in the winter as well as in the summer, and takes them in dry. So too if we left a small saucer full of water in the open air, it would slowly evaporate on a cold as on a hot day. Elicit from the class tJiat the evaporation would be more rapid in hot weather than in cold. Let us see how all this comes about 1 ? It is the air which carries off the water, and it does this because it is porous and absorbent. Sometimes the air is so very dry that its pores contain little or no vapour. Show that this may be so in cold as well as in hot weather. When this is the case the air becomes very thirsty. It breaks up the water into tiny particles, and sucks them up at once into its pores. It is the dry air that does it Sometimes the pores of the air are already loaded with water vapour, and cannot hold any more. It would be no use to hang out the clothes on such a day. They would not dry. Make the children tell why. If we go out on a hot day, just after a shower, we may see the vapour rising from the wet pavements and from the wet clothes. But at other times we cannot see the vapour, although the stones and the clothes gradually become dry, and we know that the air has taken away all the water by evaporation. The children will now be in a position to explain what is meant when we say that the water in the saucer has dried up, the clothes and the pavement have become dry, and so on. Elicit this carefully from them by a few simple questions. LES. in WATER IN OTHER FORMS 13 III. THE AIR ABSORBS MUCH VAPOUR 1. From rivers, lakes, and seas. We have seen that some of the rain which falls is at once evaporated and absorbed into the air. Much of it sinks into the earth and afterwards rises to the surface again as spring-water. This as well as the rest which is drained off the land flows away and forms rivers and lakes, and these at last find their way to the sea. The class should be made to tell all this, step by step. Lead the children to think about these great bodies of water all over the world the multitude of rivers and lakes, and the wide expanse of sea. Evaporation is constantly going on over every part of their surface, very rapidly indeed in the hot parts of the world, but even in the cold regions it is still going on. Let them imagine what an immense quantity of water is changed into vapour, and absorbed into the air from this one source. 2. From plants. Look at this bottle. Before I came to school I put into it some freshly-cut leaves, and corked it up, first making sure that the bottle was perfectly dry. What do I see now? The sides of the bottle are covered with little drops of moisture. Where did this moisture come from 1 It came from the leaves. The leaves of all plants give out moisture, and this moisture is constantly being evaporated. Lead the class to think of the trees and plants of all sorts that grow on the earth. What a, vast amount of moisture must be evaporated from them. 3. From animals. Picture a horse drawing a heavy load. His body is covered with drops of moisture. We call it perspiration or sweat. Watch what becomes of this moisture. If the weather be cold we can see it rising in vapour from his body. Watch him too as he breathes. His breath is loaded 14 OBJECT LESSONS STAND, in with water-vapour. We can see it coming from bis mouth and nostrils. If boys are set to work hard, or to run a race, what happens 1 Their bodies perspire and their breath is loaded with water-vapour. Tdl that the skin and breath of all animals are constantly giving off water-vapour, not only when they work hard but when they are at rest. This is another great source of vapour, and it is all absorbed into the air. Lesson IV WATER IN OTHER FORMS I. STEAM AND VAPOUR INVISIBLE BOIL some water in a small kettle, either over the fire or over the spirit-lamp. Call attention to the steam as it issues from the spout. Point out that we do not see the steam when it first leaves the spout. It is invisible. // first becomes visible at some little distance from the spout. Our last lesson too taught us that evaporation is constantly going on all around us that the air always contains vapour, and yet we cannot see it. The vapour is invisible. The air in this room contains vapour. Can we see it 1 No ; it is invisible. Let us prove that there is vapour in the air 1 A few minutes ago I had this tumbler of cold water placed upon the table. Look carefully on the outside of the tumbler now and tell me what you see. It is -covered with little tiny drops of moisture. Whence did these drops of moisture come ? From the water in the glass ? No. They came from the vapour in the air, which was at first invisible, but which became visible as little round drops of water when it settled on the glass. Let us see what this means. LES. iv WATER IN OTHER FORMS 15 II. CONDENSATION Here is another tumbler of warm water which has stood on the table side by side with the other. Do you see any drops of moisture on this one ? No. Now look at the steam as it comes from the spout of the kettle. Hold this slate in front of it. Examine the slate and tell me what you see. The slate is covered with little round drops of moisture. Watch me while I breathe. Can you see my breath 1 No. Now I breathe on this slate. What do you see ? Little drops of moisture. Whence did this moisture come 1 ? From my breath. How is it that you can see it on the slate ? I will tell you. The vapour of the air leaves little drops of moisture on the glass ; the steam from the kettle and the breath leave similar drops on the slates, because the tumbler and slates are cold. Cold changes the vapour into tiny drops of moisture. The vapour in the air is invisible only because it is split up into such extremely small particles that they cannot be seen. The cold causes these tiny particles to rush together, so that they are pressed into a smaller Space, and then we see them. We say that they are condensed. The steam as it first issues from the spout of the kettle is invisible. But when it meets with the colder air of the room, it is condensed or made to rush together, and we see it as it floats away. We do not usually see our breath as it leaves the mouth and nostrils. But suppose the weather is very cold 1 Our breath then becomes visible. Why ? Because the cold air around us condenses the vapour of our breath as it leaves the mouth and nostrils. 16 OBJECT LESSONS STAND, in III. FOGS AND CLOUDS Evaporation, then, is always going on around us from the earth, from seas and rivers and lakes, as well as from plants and the bodies of animals. We do not usually see the vapour in the air, because it is in such very small particles. Sometimes, however, the air looks thick and dense, as though it were loaded with dense white smoke. We cannot see across the road. We say there is a fog. Let us see what this means. The usual evaporation has been going on, but the air around has been cold and has condensed the vapour as it was absorbed into the air. This condensed vapour is the fog. When the air around us is not cold, the vapour arises without our seeing it, and floats away over our heads until it meets with cold air above. Lead the class to tell that this cold air condenses the vapour in those higher regions, and forms what we call a cloud. Lead them to talk about a fog, its nature and appearance, and then explain that a cloud is exactly the same as a fog. People who travel over mountains often find themselves in the midst of a dense cloud, which hangs over the mountain. They walk through the cloud just as we often walk through a fog. IV. RAIN MIST DEW We now understand what clouds are, and you all know that rain comes from the clouds. Whenever we look up at the sky we can see clouds ; but the clouds are not always sending down rain. Let us see why this is so. The clouds consist of vapour condensed into little particles which are just able to float in the air. If the cloud passes through still colder air, further con- LES. v SOLID WATER 17 densation takes place, and these little particles rush together and form drops of water which are too heavy to float in the air. They then fall to the earth as rain. Sometimes the drops formed are very small indeed, although too heavy for the air to hold. They fall as extremely fine rain, and we say it is a mist. Sometimes after a warm day the air becomes suddenly cold at night. The evaporation is of course going on rapidly, but as the vapour is formed it becomes rapidly condensed on the cold surface of the ground, the grass, and the leaves. In the morning we see grass, leaves, ground covered with little round drops of water. This we call dew. Lesson V SOLID WATER I. ICE HERE is a piece of ice. Ice is solid water. Take it in your hands and tell me some of its properties. Draw from the class in this way that it is a hard, brittle, transparent, solid body ; has a definite shape of its own, which can only be altered by breaking ; and it can be grasped in the hand. Could you find a piece of ice in the road or on the ponds this morning 1 No. Why not 1 The weather is not cold enough. What has cold to do with it ? Cold changes the liquid water into solid ice. This piece of ice was once water like that in the tumbler. Ice and water are the same substance in different forms. Tell me some other substances we have seen in both solid and liquid form. Butter, wax, sugar, sulphur, lead. VOL. II C 18 OBJECT LESSONS STAND, in Now here is a piece of solid butter. How can we change it into the liquid form ? By heating it. How do we describe the change that takes place in the butter when it is heated ? We say butter melts. It becomes a liquid, flows about, and takes the shape of the vessel which holds it. Lead up from this to show that the same process is at work when we melt wax, sugar, sulphur, or lead. They all melt with heat. Let one of the children Iwld a piece of the ice in his hand while some lead is being melted in an iron spoon over the spirit- lamp. The melted lead is a liquid. Now show me the piece of ice you have been holding. What have you been doing to it ? Call the attention of the class to tJie way in which it has dis- appeared. It has become liquid, gradually trickled through the boy's fingers, and fallen away in drops. Why ? The heat of boy's hand melted the ice. Lead them to tell that butter will melt in the hand too, but that sugar, wax, sulphur, and lead would not Jiave melted. Why 1 They require more heat to melt them. Melt a piece of ice in the spoon to show how rapidly it melts. Now look at the melted lead in the spoon. Why, it has become changed into the solid form ! Let the boys examine the lead in the spoon and see that it has become solid again. Lead, like other metals, is only seen as a liquid when under great heat. The heat being removed, we say it gradually solidifies. Melted sugar, wax, sulphur, butter also become solid as they cool. Now look at our melted ice. Has that become solid yet ? Would it ever become solid again ? Yes, if we could make it cold enough. If 1 were to put this water into a very cold place it would become solidified again into ice. You would say the water had frozen. LES. v SOLID WATER 19 Lead ihe class now to explain that ice and these other sub- stances that melt are all alike. 1. They liquefy with heat, although some want more heat than others. 2. They solidify when the heat is removed. Water, however, has to become very cold indeed before it becomes solid. IT. ICE IS LIGHTER THAN WATER Put this cork into water. What happens ? It floats. Put this stone in. What happens ? It sinks. Why does cork swim and stone sink ? Cork is lighter than water ; stone is heavier. Now put this piece of ice into the water. It floats. What does this prove ? Ice is lighter than water. Lead up from this to make the class talk about the frozen ponds in winter-time. Where do we find the ice ? On the surface. Is the whole pond solid ice 1 No. Tell of the fishes and plants that live in the water. What would become of them if the whole of the water in the pond froze into solid ice ? They would be frozen and destroyed. There is only a sheet of ice covering the surface of the water. It is lighter than the water itself, and so it floats on the top. When it breaks we see the water below. Tell that this sheet of ice on the top actually protects the wafer against the biting cold. Without it, fishes and water-plants would die. III. HAIL Sometimes we hear a loud pattering on the window panes and we see the ground strewn with little round drops of ice. We call this hail, and we say there is a hail-storm. We pick up some of the little balls to examine them, but they melt in our hands. 20 OBJECT LESSONS STAND, in What are they ? They are really frozen rain-drops. Rain falls in little round drops. Imagine these drops to be frozen suddenly as they fall, and then you will under- stand what hail is. The rain is frozen into hail when it passes through some very cold air as it falls. IV. SNOW Lead the class to talk about a snowstorm. What do we call the little particles of snow as they fall } Snowflakes. How beautiful they look; how light and feathery ! When the snow lies on the ground we can take it up in our hands and make it into a hard, solid ball. If we hold snow in our warm hands what happens? The snow melts into water and runs away through the fingers, just as was the case with the ice. Snow, then, is another form of solid water. Where did it come from ? Carry the class back to talk about the evaporation constantly going on all around us the vapour rising, at first invisibly, then condensing into fog, mist, or cloud. Let them imagine the air around this condensed vapour to become suddenly cold cold enough to freeze the tiny particles of condensed vapour. These little particles of frozen vapour then become solid water, and must fall as snow to the earth. Tell the uses of snow in protecting the earth and the plants from frost. It is really a thick blanket which will not let the heat pass away. When, therefore, our fields and gardens are covered thick with snow, whatever warmth there is in the earth is prevented from passing away, while at the same time the Siting frost cannot get through to nip the plants beneath. LES. VJ MERCURY ITS PROPERTIES 21 Lesson VI MERCUKY ITS PROPERTIES SHOW some mercury in a bottle. We have talked about metals of various kinds. Here we have a new metal. We have also seen liquids of various kinds. This is a new liquid, a liquid metal. We call it mercury. Call attention to its silvery-white colour and its bright metallic lustre. In appearance it is very like silver. Tell that it never tarnishes on exposure to the air always keeps its bright surface. It is a liquid. See, I can pour it into this saucer. Let fall a drop on a slate. It instantly breaks up into a multitude of tiny round drops. Tilt the slate slightly. The little drops run about rapidly as the slate moves. Tell that because of this it is sometimes called quicksilver. If I pour some water on a slate, I wet the slate, and the water leaves a mark wherever it flows. What do we notice about the mercury ? It does not adhere to the slate, each little drop rolls about without leaving any trace. Let the children test it for taste and smell, and lead them to tell that mercury is tasteless and inodorous. Let them next take the saucer of liquid metal in their hands, and lead them to tell of its great weight. It is heavier than any of the common metals. It is nearly fourteen times as heavy as water. Make the class tell 1. That gold, silver, copper, cast iron, steel, although fusible, require intense heat before they will become liquid. 2. That lead and tin can be melted in a spoon over an ordinary fire, for they are more easily fusible than those metals. 22 OBJECT LESSONS STAND, in Here, however, we have a metal the only one which is always melted, always in the liquid form, at the ordinary temperature in this country. Mercury is more fusible than any other metal. In some very cold parts of the world mercury becomes frozen into a solid in the winter, but it is never solid here. In the solid state it is malleable like other metals. Here is some water. Suppose I heat some of it in this glass tube over the spirit-lamp. What will happen 1 The water will boil, and pass away in vapour. Now instead of boiling the water, we will boil some of this mercury in the tube. Call attention to the violent commotion in the liquid as it becomes heated. Explain that the mercury is boiling rapidly. Lead the class to tell that water ads in exactly the same way when it is subjected to heat. Point out the tiny metallic globules which soon begin to collect on the cold sides of the tube. What are these 1 Explain that, as it boils, the liquid mercury is rapidly changed into vapour. This vapour is invisible at first, but as soon as it touches the cool sides of the glass tube, it condenses, and becomes visible as little silvery globules. Refer now to boiling water, and show the continued similarity of action in each. There is the same bubbling commotion among the particles and the same evaporation of the liquid into invisible vapour. What would happen if I were to hold a cold slate in the steam as it rises from the boiling water ? The vapour would condense as little round drops of liquid water, just as we have seen the mercury condense on the sides of the glass tube. Mercury, although it rolls about on most bodies without even wetting them or adhering to them, readily mixes with LES. vii MERCURY 23 other metals (e.g. gold, silver, lead, tin) without being heated. It forms with these metals a compound known as an amalgam. Lesson VII MERCURY I. RECAPITULATORY LEAD the class to describe the properties of the metal, as they were given in the last lesson. Dwell specially on its distinguishing characteristic as being a liquid metal. This is the state in which we always meet with mercury in countries like ours. But is it ever seen in any other than the liquid state ? Lead the class to tell that in some extremely cold parts of the world, mercury freezes, and that in the solid state it becomes very similar to other metals. It may even be hammered out and rolled, for it is quite malleable. Let them tell that they have actually seen it in another (the gaseous) state. When, we boiled the mercury in the tube, it acted just as water does when boiling, and mercury vapour rose from the liquid metal, and settled in little round balls on the sides of the tube. Lead them to tell of the mercury amalgams, and how they are formed by the mercury uniting with other metals such as gold, silver, lead, tin. A dear understanding on this peculiarity is essential for what is to follow. All these facts should be questioned out from the children. II. How MERCURY is FOUND Mercury, like other metals, is usually met with in the form of ore. The ore is like a hard reddish-brown stone, with very little metallic lustre. It is known as cinnabar, and contains in addition to the metal mercury a large quantity of sulphur. 24 OBJECT LESSONS STAND, in This cinnabar is dug out of deep mines in various parts of the world. The metal is obtained from the ore by roasting. The ore is broken up into small pieces, then mixed with quicklime, and set on fire. Lead the children to think of their former lesson on sulphur, and make them tell how the sulphur of the ore would act under the roasting process (the teacher assisting, of course, where necessary). Eefer also to the evaporating properties of mercury. If there is any mercury in those pieces of roasting ore, what will become of it as the roasting goes on ? It will pass away as vapour. The mercury is wanted; hence this vapour must be collected as it rises. Tell that the vapour is made to pass through cool earthen- ware pipes. Let the class explain the rest. The vapour condenses on the pipes in round globules of liquid metal, which can be poured off and collected ready for use. Tell that in a very few places pure mercury is found in holes of the rocks. Almost all the mercury we get, however, is obtained from the ore cinnabar. III. USES 1. For extracting gold and silver from the ores. Eefer again to the strong affinity of mercury for these metals. Let the class tell that it at once unites with the gold or silver and forms an amalgam. We may pour mercury on most other bodies, and the tiny drops of the liquid metal will roll about amongst them without adhering to them, without even leaving a trace. But the mercury no sooner touches gold or silver than it adheres to them and forms an amalgam. LES. viu ALCOHOL 25 The ores, crushed very fine, are mixed with a certain quantity of mercury. The mercury seizes upon the little particles of gold and silver to form an amalgam, but it will not combine with the earthy parts of the ore. These earthy parts are gently washed away in shallow troughs, and the amalgam is collected and gently heated. What happens then ? The mercury flies off as vapour, and is condensed and collected for future use. The pure gold or silver remains behind. 2. For silvering the backs of looking-glasses. Mercury is specially adapted for this purpose, because of its bright metallic lustre. Tell that an amalgam of mercury and tin-foil is made, which is caused to adhere by pressure to the glass. The process can be explained in a later lesson. 3. For the preparation of vermilion. Show a little of the bright red powder, and tell its use in the preparation of paint. 4. For medicines. Medicines containing mercury ought to be carefully avoided, as they are all more or less poisonous. They should never be taken except under the doctor's advice. The grey powders frequently given to infants and the powerful blue pill both contain mercury. The use of this metal (mercury) in making various instru- ments (such as thermometers and barometers) will be dealt with in later lessons. Lesson VIII ALCOHOL PROPERTIES Snow some spirits of wine in a bottle. Here we have another new liquid. We will examine it and find out some of its properties. 26 OBJECT LESSON'S STAND, in Lead the children to describe its colour, odour, and taste. It is a clear transparent liquid ; it has a strong odour. Let one of them apply the tongue to it, and explain that it has a sharp, biting taste. Pour a little of the liquid on a child's hand, and let the class observe what happens in a very short time. What has become of the liquid? See, the hand is quite dry. Tell that alcohol evaporates very rapidly. The spirit that was poured on the hand immediately began to fly off and disappear in vapour, until none was left on the hand. If the cork were left out of the bottle for a short time, all the liquid would evaporate and disappear in this way. Bottles containing alcohol, therefore, must be well corked. We have a name for substances which evaporate and fly off in this way. We call them volatile sub Stances. Volatile means " able to fly off." Alcohol, then, is a very volatile liquid. Next lead the child to describe the sensation he felt in his hand as the alcohol evaporated. He will tell that the hand felt cold. Why was this ? Explain that as the spirits evaporate they rob the hand of heat, and it is the loss of that heat which causes the hand to feel cold. Pour a little of the spirit into a saucer, and apply a lighted taper near it. It takes fire at once. Show that before the taper actually touches the liquid, it bursts into sudden blaze. Why ? Because the liquid is volatile and vapour is rising from it. What shall we say about alcohol, because it takes fire in this way 1 It is a highly inflammable liquid. Here I have a piece of camphor ; I will put it into this alcohol. What happens ? The alcohol dissolves the camphor, so that it disappears. Water will not dissolve it. LES. ix ALCOHOL 27 Notice what takes place when I pour the solution of camphor into this glass of water. The dissolved camphor at once returns to the solid state, and may be seen floating about in little feathery flakes in the water. Camphor is insoluble in water, but soluble in spirits of wine or alcohol. Alcohol is also a solvent for many oily and resinous substances. Break an egg, and pour the " white of the egg " (albumen) into a glass. Let the children examine it. Now add carefully some alcohol, and let them observe what takes place. The alcohol changes the clear transparent albumen to a white solid substance. We may say that alcohol coagulates the albumen. Explain carefully the meaning of the term. Tell that it does this because alcohol has a very strong attrac- tion for water. It robs the albumen of every particle of water it contains, and this changes the appearance of the substance itself. Lesson IX ALCOHOL I. INTRODUCTION COMMENCE with a brief recapitulation of the subject-matter of the last lesson, so as to make the children tell, by means of a few well -chosen questions, the properties of this liquid as they were described. Deal specially with its volatile nature ; its power as a solvent for substances insoluble in water ; its action on albuminous sub- stances ; its inflammability. 28 OBJECT LESSONS STAND, m II. WHAT IT is Prepare, a day or two beforehand, a mixture as follows : Fill a glass vessel, nearly to the top, with water slightly warmed ; add to the water enough molasses to colour it a deep brown, and then put in a spoonful of yeast. Set the vessel aside in a warm place where an even temperature can be maintained, until it is required for the lesson. Show the vessel, and tell what has been done. It contains simply a mixture of sugar and water, for molasses is really sugar. Show some yeast. Explain whence it came. Describe its nature. It is really a plant. Tell of its rapid growth and its power of making other things grow. In the cask it is always "on the work." We do not say it grows. We use another word. We say it " ferments." Tell of the baker " setting his sponge " to make bread. He mixes the flour and water and adds a quantity of the yeast. The yeast at once commences to work, and ferments the whole of the dough, so that by the end of six or eight hours the mixture swells up or rises, and resembles very much in its spongy appearance the yeast itself, because fermentation has been going on in the dough. The mixture of molasses and water in the glass has been undergoing the same process of fermentation during the last two days. Let the children test the mixture for odour and taste, and they will at once detect the same strong smell and the same sharp biting taste as we noticed in the spirits of wine. The fermentation caused by the yeast has changed the sugar into a new substance, alcohol. Alcohol is the chief constituent of wine, spirits, beer, and all fermented liquors. Wines are made from the juice of the grape, etc. LES. ix ALCOHOL 29 This juice contains sugar but not alcohol. It is only after fermentation that the sugar is changed into alcohol. Brandy is made from the spirit distilled from wine, which is, strictly speaking, the actual " spirits of wine." Rum is the spirit from fermented molasses. Beer is made by fermenting the sugar of malt. Tell briefly of the preparation of malt from barley, with the result that the starch of the grain is converted, by the process, into sugar. It is in this state called malt. The sugar of the malt is changed by fermentation into alcohol. The methylated spirit which we burn in our spirit- lamp is also a crude and rough kind of alcohol, produced from various substances, but always by the same process of fermentation. Ill USES Show that the uses of alcohol are dependent on its properties. 1. It is volatile, and as it evaporates, takes away heat. Hence applied to the skin it allays inflammation. Explain the term carefully. 2. Its greediness for water causes it to coagulate albumen. It is hence used to preserve specimens for museums, hospitals, etc. Explain. 3. Its great inflammability renders it useful for burning in our spirit-lamps. 4. It is used as a solvent for substances which are insoluble in water and all other liquids. The lesson should not be closed without a few practical and sensible remarks on the abuses of alcoJwl. TJiese need not be tabulated here. The teacher mil select such facts and hints as he thinks best, having regard to the age and capacity of the children. 30 OBJECT LESSONS STAND, in GASES Lesson X AIR I. Am is A MATERIAL SUBSTANCE SEE, here is a glass flask with a long neck and an open mouth. Let us pour in water until it runs over the top. What do you say about the flask ? It is full of water. Now I will pour it all out again, and you will perhaps tell me that the flask is empty. But is it really empty? Let us see. Watch while I press the flask, mouth downwards, into this basin of water. If the flask were empty there would be no reason why the water should not rise to the same height inside the neck as outside. Now tell me what you notice about the water as we press the flask down. The water rises only a little way up the neck of the flask. It is not so high as the water in the basin outside. Let us try the same thing with this piece of glass tube. I press that down into the water. What do you notice 1 The water inside the tube stands at the same height as that in the basin. Now I close one end of the tube with my thumb, and press down into the water as before. The water inside the tube is not so high as that in the basin. We might press the flask or the closed tube down ever so far, but it would be impossible to fill them with water. Why 1 Because they are already filled with some other substance. The flask appears to be empty, we cannot see anything in it. LES. x AIR 31 Notice what happens when I slant the flask on one side. There is a sudden gurgling sound, and something passes out of the flask and bubbles up through the water. And as this something leaves the flask the water rushes in, and now we may see the flask full of water. What is this something that came out of the flask ? Air. So then this " empty " flask is really full of air, and our experiment proves that air is an actual substance. It occupies all the space of the flask, and so long as it is in the flask the other substance, water, cannot enter. Air, then, is an actual substance, and occupies space although it is invisible. All the substances we have hitherto dealt with we have been able to see, and, to some extent, handle. Here we have a new kind of substance altogether; a substance which is invisible, although we know it is as surely a material body as those. But let us see why the water rises in the open tube, while it cannot rise when I close the upper end. The air is in the tube in each case. When the tube is open at the top, the air can escape as the water rises from below. The air, in fact, passes out from the top to make room for the water to enter at the bottom. II. AIR is AN ELASTIC SUBSTANCE Lead the class to tell that in the experiment with the flask and the dosed tube we noticed that the water entered a little way into }he neck or the tube as we pressed downwards. It did this because it was able to squeeze or compress the air into smaller space. When we ceased to press, the air sprang back to its original bulk again. Air is compressible and elastic. Compare with the elasticity of the sponge. Illustrate by means of a bladder filled with air and an air-tight syringe. 32 OBJECT LESSONS STAND, in Show that the bladder may be squeezed till the air within it occupies a much smaller space, but that as soon as it is left alone it springs back to its original shape and size. Close the nozzle of the syringe securely, and then press the piston down. What is there inside the syringe ? Air. The syringe is full of air, but I can press down the piston, because the air is compressible, and can be squeezed into smaller bulk. Now let go the piston. It springs back at once, because the air is elastic. Lesson XI AIR I. AIR HAS WEIGHT REMIND the class that air will force itself into every space every nook and corner. Even what we call " empty " is really "full of air." It is a difficult matter to remove the air out of any vessel. Tell that there is an instrument, however, called an air- pump, which will remove the air from a vessel. Show one if possible. Exhaust the air from the receiver to show its action. It is found that after the air has been removed in this way, the vessel weighs less than it did before. Imagine a square box measuring a foot each way. Such a box would weigh about an ounce less after the air had been pumped out of it than it did before. What does that show ? That all the air in that box weighs about an ounce. IL AlR PRESSES EQUALLY IN ALL DIRECTIONS 1. Fill a test-tube with some coloured liquid. Close the mouth of the tube with the thumb, and invert it in a basin of water. LES. xi AIR 83 Let the class note and describe what takes place. Why does the liquid in the tube not run out into the basin ? Tell that the weight of the air presses downwards on the surface of the water in the basin ; that this pressure is greater than the weight of the liquid in the tube, and so prevents that liquid from flowing out. Air, therefore, presses downwards. 2. Fill a tumbler, or the same test-tube, quite full of water. Cover the mouth with a piece of writing-paper, and carefully invert the vessel, pressing the paper meanwhile with the palm of the left hand. The hand may now be removed, without either the paper fatting or the water running out. The water is very heavy, and is pressing with all its weight downwards on the paper. Why does the paper not fall? Something must be pressing with greater force upwards. What is there between the paper and the floor? Nothing but the air. Then it is the air which presses upwards against the paper, and so prevents the water from falling out of the glass. Air, therefore, presses upwards. 3. Illustrate further with a boy's leather sucker. Lead the children themselves to explain, step by step, the action of the sucker, and why it adheres to the stone. Why must the stone have a smooth surface ? In order that no air should get between the stone and the sucker. Lead the children to see that the result is the same the sucker adheres equally well whether it is placed upwards, down- wards, or sideways upon the stone. The air in each case presses the sucker to the stone. The air presses with equal force, therefore, up- wards, downwards, sideways, and in all directions. VOL. II 84 OBJECT LESSONS STAND, in Lesson XII GASES I. NATURE OF A GAS COMMENCE by leading the boys to think over the subject of the last lesson. Let them tell that air, though invisible, is really a material substance, which occupies space and has weight like other bodies. We shall now have to turn our attention to other sub- stances which resemble air, and differ from both solids and liquids. Let us begin by turning on one of the gas-burners for a few moments. Tell me what you can see. There is nothing to be seen. Yet we can hear by the rushing sound that there is something passing out of the pipe. I will try and grasp some of it in my hand. I cannot grasp it ; but I learn in another way that there must be some substance there, for I can smell its powerful and unpleasant odour on my hand. See, if I bring a light near, I can learn in another way still that there is an actual substance coming out of the pipe, for it takes fire and burns with a bright dame. What do we call this substance 1 Gas. Yes ; and its proper name is coal-gas, for it is prepared from coal. Show Ihe similarity between this substance and the air which we dealt with last lesson. All bodies of this nature are called gases. Air is a gas, and the invisible vapour in the air is a gas water-gas. Make the class tell the distinguishing characteristics of solids and liquids, and contrast them with gases now under considera- tion. LES. xii GASES 35 Tell that there are many other gases besides those we have mentioned. Some gases do not burn, and some have no odour. The air is of course one of these. Most gases are invisible, but some day we may deal with gases which may be seen. All, however, are alike in being thin, light bodies, differing from both solids and liquids, like the air we breathe and the coal-gas we burn. II GASES AND LIQUIDS 1. How they resemble one another. Make the class tell that liquids can be made to flow. Show that gases also can be made to flow. If the pipes were filled with water instead of gas, and I turned the tap on, what would happen 1 Now how does the gas pass from one end of the school to the other 1 It flows along the pipes. (a) Illustrate with a pair of bellows how air can be made to flow. Every movement of the bellows drives the air out in a stream. Tell also that the wind is air in motion. (b) Prepare some carbonic acid gas, before the lesson, by pouring dilute hydrochloric acid on some small broken pieces of chalk or marble. No heat is required/ the gas is rapidly generated, and may be easily collected by dipping the end of the tube into an empty bottle. Show the jar or bottle containing the gas. The gas is in- visible. Tell its name. Show how it can be poured i.e. how it can be made to flow from the jar into some other vessel. Prove that it does actually pass into the other vessel. It will extinguish a lighted taper as it flows. Hold the lighted taper between the two vessels. Show that the gas is flowing from one to the other. In its course it ex- tinguishes the flame. 2. How they differ. A short time ago we allowed the gas to escape from the burner, and can now smell it in every part of the room ; in fact, the gas seems to fill the room. Why didn't I take a pail or basin and collect the 86 OBJECT LESSONS STAND, in gas as it passed away ? If it had been water I could have collected it without any trouble. The water would have flowed into the vessel, taken the shape of the vessel, and its surface would have been level. Draw these facts from the class. Why cannot I collect the gas in the same way 1 The reason is that gases are substances which have no surface. They are constantly trying to spread themselves out in all directions. A very small quantity of gas put into any vessel would rapidly fill the whole vessel. The small quantity of gas which escaped from the pipe has long before this spread itself out until it fills the whole room. We can smell it everywhere. It could not be kept in any one part of the room. I can put into this tumbler any quantity I choose of sand, sugar, or water, and it will remain as I put it in the glass. But I cannot half fill this glass with gas of any sort. If I put in a very small quantity, it at once spreads out till it fills the whole glass. Refer to the experiment in last lesson. What happened when I pressed the inverted flask down into the water ? The water rose a little way in the neck of the flask. What did that prove ? That the air was compressible. Let us try the same thing with some of the coal-gas from the burner. I will collect some in this test-tube from the burner. Now let us force the test-tube, mouth downwards, into the water. Note what happens. The water again rises some little way up the tube, showing that we are squeezing or compressing this gas into a smaller space as we press down. Tell that not only these, but all gases are compressible and elastic fluids. So, then, gases differ from liquids in that they have no surface and are constantly changing their form and size. A.ny quantity of a gas, when it is put into a vessel, at once LES. xni COAL-GAS 37 fills the whole space, and any quantity (like that in the flask) can be squeezed or compressed into a smaller bulk than it once occupied. Lesson XIII COAL-GAS I. PROPERTIES REFER to the last lesson, and lead the children to tell the pro- perties of this gas as far as they have already been described. It is invisible, it has a powerful and unpleasant odour, is very inflammable, and burns with a bright flame. Tell that another important property is its explosive nature when mixed with air. Illustrate this explosive property by the soda-water bottle experiment, as explained in the lesson on " Coal." As time may not allow for the collecting of the gases during the lesson, it will be well to have the bottle filled and corked beforehand. N.B. Use care, and wrap the bottle well up in a thick cloth before applying the light. Coal-gas when mixed with air is very explosive. It sometimes happens that, through carelessness, a gas-burner is left turned on, the gas escapes and fills the room, and we have all the materials for an explosion our soda-water bottle experiment on a terrible scale. All that is wanted is a light. Never take a light into a room if you can smell gas. You are perfectly safe without a light, no matter how much gas has escaped. Go in, open doors and windows, and all will be safe. Why open doors and windows? Gases are always trying to spread out into greater space. The gas will soon 38 OBJECT LESSONS STAND, in pass away out of the room into the open air and fresh air will flow into the room. When this has taken place it will be time enough to find out where the gas is escaping. n. COAL-GAS IN THE MINE Refer to some of the earlier lessons, and lead the children to think of a coal-mine, its work and its workers. The mass of coal in the mine gives off great quantities of this gas. The miners call it fire-damp. Lead the children to tell that the miners must have a light of some sort. A candle or an ordinary lamp would not do, for the flame would catch the gas, and there would be an awful ex- plosion. Show a picture of the Davy lamp, or (if it can be obtained) one of the actual lamps themselves. Tell that every man who goes down into the mine is provided with one of these lamps lighted and locked, and if he obeys his orders he is quite safe. Should he open his lamp, however, but for a second, the fire-damp will immediately explode. Show the construction of the lamp. The burning flame is covered in and completely surrounded with wire gauze. To illustrate the principle of the lamp, hold a piece of common iron wire gauze over the gas-burner, turn on the gas, and light it above the gauze. Raise the gauze some inches above the burner, and show that tJie flame is still on the upper side only. Of course the gas is passing upward from the burner to the gauze, but it does not take fire below the gauze. Why ? The iron wire of the gauze does not get red hot, and will not set fire to the gas below. Here we have a lamp surrounded with this wire gauze. If there is any gas in the mine, it will pass through the meshes of the gauze into the lamps and burn there around the flame, but the flame itself will not pass through the gauze, and so the air in the mine is safe from explosion. LES. xiv COAL-GAS 89 Lesson XIV COAL-GAS I. HOW THE GAS IS MANUFACTURED THE coal in the mine gives off gas, as we see, of its own accord. We want gas for many useful purposes, and we manufacture it from coal. Try to follow what I am going to do, and you will understand something about the making of gas. I have here some coal powdered very small. I am going to put it into the bowl of this long clay tobacco- pipe. Now it is nearly full, I will cover the top with some soft clay. N.B. If this could be prepared beforehand so much the better, as the experiment is more successful when the clay is well dried. In this case simply tell what has been done and show some of the finely-powdered coal. Fasten the bowl of the pipe over the flame of the Bunsen burner, or thrust it in the fire. In a short time a dense yellow smoke will be seen coming out of the end of the stem. Apply a light, it burns with a yellow flame. This smoke is coal-gas. It is not clear and invisible, because it has not yet been purified. Some of this gas may be easily collected in a test-tube, over a bowl of water, for examination and experiment. Place the end of the pipe stem in the basin of water and after filling the test-tube with water, invert it and hold it mouth downwards over the end of the stem. The gas will fill the tube by displacing the water. Show that this gas will take fire and burn in the test tube as soon as a light is brought near it. Use this experiment to explain the way in which gas is made in the great gas-works. Instead of the bowl of the pipe, with its pinch of coal-dust, lead the children to imagine strongly-built closed chambers 40 OBJECT LESSONS STAND, ill called retorts, made of fire-brick and iron, each capable of holding nearly a quarter of a ton of coal ; instead of the stem, long iron pipes ; and instead of the test-tube, enormous iron-plated gas-holders, many times bigger than this school. II. ITS USES Lead the children to tell as many of the uses as they can. 1. The first and most important use to which we put the gas when we have prepared it is for lighting purposes. 2. Gas is also burned now very largely in specially con- structed stoves for cooking and warming purposes. 3. A certain kind of engine, commonly called a gas- engine, is worked entirely by gas. 4. It is also used for inflating balloons. Picture to the class a large balloon just set free and floating in the air. Why does it rise and float in the air ? Let us see. Suppose I put this cork at the bottom of the basin of water. What happens when I let go? It rises to the surface. Would a stone rise ? No. Why, then, does the cork rise and the stone not ? The cork is lighter than the water ; the water pushes the cork upwards. Tell that cork life-belts are used to save people from drowning. They not only float themselves, but are able to support a man's weight and keep him from sinking, because they are so much lighter than water. Pass from this to the balloon, which is made to float in the air. The balloon itself is only a large silken bag, but it carries the weight of a car, and one or two men in it. Yet the whole floats steadily in the air. What does that prove 1 That the whole machine, car, men, and all, are lighter than the air in which they float How can this be ? LES. xv OTHER PRODUCTS OF COAL 41 Tell that the great silk bag is filled with coal-gas, and that this coal-gas is only about half as heavy as air. When the great bag is full of the gas, therefore, it is not only able to rise in the air itself, but is able also to carry up with it car and men too. Lesson XV OTHER PRODUCTS OF COAL I. TAR Snow some common tar. Let the boys tell its name, and say something about its principal use for covering wood-work. (a) What it is. Lead them to describe again the process of gas-making, the great, closed retorts filled with tons of burning coal, the long iron pipes leading from the retorts to carry off the gas, the change of coal into coke by the burning, and so on. Now suppose we put a piece of coal on the fire and watch it burn. What do we see besides the blaze ? Some thick yellow smoke. Think of our tobacco-pipe experiment. What came out first? Some thick yellow smoke. It is just so with the retorts in the gas-works. Not only gas, but dense volumes of thick smoke are given off by the coal as it burns. The long pipes which lead from the retorts pass into great tanks of water, so that all that comes from the burning smoke, gas, everything must pass through the water. The gas, being much lighter than the water, bubbles up to the surface, and passes away by other pipes for further purifying, and at last is collected in great receivers or gasometers. The water condenses the smoke and it falls to the bottom of the tank as a thick black liquid. This is tar. (b) Its properties. Let the children examine the tar 42 OBJECT LESSONS STAND, in again, and deduce such properties as they can find by observation. It is a thick, black, shiny, sticky fluid, something like treacle in appearance, it has a powerful and peculiar smell, and bitter taste. Put a little on the hand and try to rub it off. It will not rub off. Try and wash it off. It will not wash off. What must I do ? Rub some grease or turpentine on the hand. Note what takes place. The fat and the tar mix, the fat dissolves the tar, and I can now easily wash it off with soap and water. Why could I not remove it before ? Tar is insoluble in water and will not mix with water. Pour a few drops of tar into a glass of water. What becomes of them t They do not mix with the water, but sink to the bottom and remain there. Where do the people of the gas-works find the tar? At the bottom of the tank. It will not mix with the water, but settles at the bottom. As it always sinks to the bottom of the tank, we know that tar is heavier than water. Now dip this piece of paper into the tar, and light it. It blazes up and sends off dense clouds of smoke. It is very inflammable. Tell that one of the chief properties of tar is its power of preserving other substances, especially wood, and preventing them from rotting. Wooden sheds, palings, any structures that are to stand the weather are usually covered with a coating of tar. Wooden posts that are to stand in the damp earth or in water are always dipped into tar beforehand. Why ? Water and tar will not mix ; the water simply runs off the surface, and cannot penetrate through the tar to rot the wood beneath. II. FURTHER PRODUCTS OF TAR The tar, as it is obtained from the condensers, is a mixture of many distinct substances. LES. xvi PARAFFIN 43 Coal-naphtha. If the tar is put into a retort and heated, the volatile parts rise in the form of vapour. This vapour is allowed to pass off into condensers, and forms at last a rough, crude spirit oil, known as coal-naphtha. That which is left behind in the solid state forms a sort of pitch. Coal-naphtha is sometimes burnt in a rough kind of lamp in the open air, but is very dangerous. It is used also as a solvent for india-rubber, gutta percha, and sulphur. Show the inflammability of the oil by moistening a piece of paper with some of it, and then applying a light. Lesson XVI PARAFFIN OIL I. WHAT IT is LEAD the class to tell all they can of the liquid naphtha, and its properties. We call it coal-naphtha. Why 1 It is obtained from coal in the process of gas-making. This coal-naphtha is one of a large class of similar inflammable liquids, all of which have nearly identical properties. Many of them are not manufactured, as the coal-naphtha is, but are obtained direct from the ground. The commonest of all these naphthas is known as petroleum or rock-oil. Rock-oil is obtained from springs in many parts of the world, but chiefly in America and Russia. The oil springs in some places rise to the surface of the ground, but as a rule deep wells are sunk and the oil is pumped up from them. The petroleum as it comes from the earth is of a dirty greenish-yellow colour, and very thick and oily. It has a 44 OBJECT LESSONS STAND, m very powerful and disagreeable smell, and in this state is quite unfit for use. It is pumped from the wells into great tanks, whence it is sent along iron pipes to the refineries to be purified and separated into the various things of which it consists. Note that in one of these oil regions in America there are more than 2000 miles of these underground iron pipes for carrying the oil. A similar crude oil is obtained by various processes from peat, from bituminous coal, especially from the Boghead cannel coal and, as we have seen, from coal-tar. In the refinery it separates into 1. A clear liquid for burning in lamps, and commonly known as paraffin oil. (That obtained from petroleum or rock-oil is called kerosene.) 2. A beautiful, fine, white, wax-like substance, solid paraffin, used largely in making candles. 3. A rough, coarser kind of oil, for lubricating or oiling machinery. Note that benzoline is obtained from coal-tar naphtlia by the same process of refining. It is a clear, colourless liquid, much used for burning in lamps instead of oil or spirit. Show and describe one of the small sponge lamps used for this purpose. Like naphtha itself, benzoline is a solvent for india-rubber and gutta perch a. It also readily dissolves fatty matter, and is therefore much used for removing grease stains from silks, satins, and other articles. II. PROPERTIES Lead the class to tell, as before, those properties which can be learned by simple observation. Paraffin oil is a clear, colourless liquid, and has a very powerful and unpleasant smell and taste. Pour a little into the glass of water. WTiat happens to ill It floats on the surface. LES. xvi PARAFFIN 45 Paraffin oil is therefore lighter than water. Plunge a lighted match into some paraffin oil, and let the children note what takes place. The oil does not take fire; in fact it actually puts out the burning match. The oil itself will not burn. What a strange thing this is, for we use it to burn in our lamps and stoves. If possible, show a paraffin lamp burning. Call attention to the wick. Tell of its porous absorbent nature. Tell also that paraffin oil when it is heated gives off an invisible gas or vapour. Now lead the children to follow up for themselves the steps of the burning in the lamp. The wick absorbs the liquid oil through its pores ; the liquid is evaporated into a gas or vapour by the heat of the flame, and it is not the oil itself, but this gas from the oil that burns, just as the ordinary coal-gas burns in our gas-pipes. There is no danger in the use of paraffin oil, unless it is allowed to become heated. When it is heated, it, as we see, gives off a gas, and this gas, like coal-gas, when mixed with air is very highly explosive. Benzoline is more dangerous than paraffin, but from the same cause. The heat of an ordinary hot day is sufficient to evaporate it, and the gas from it is highly explosive when mixed with the air. Test the inflammability of benzoline by pouring a very small tea-spoonful into a saucer, and applying a taper, as we did with the paraffin oil. It blazes up in an instant. Explain that, as in the case of the paraffin, it is the gas from the liquid and not the liquid itself that burns. Warn the children never to meddle with this liquid after dark, either for trimming the lamps or for any other purpose. 46 OBJECT LESSONS STAND, in Lesson XVII CARBONIC ACID GAS I. HOW TO MAKE IT WE have seen some of the properties of this gas. We are now going to find out something more about it. But first I want you to watch me while I prepare a little of it for you to examine. I have here some broken pieces of marble (limestone or chalk will do quite as well). I will put them into this bottle, which is fitted with a bent tube and a funnel. Now I will pour enough water down the funnel into the bottle to just cover the pieces of chalk, and then add a little of this liquid (hydrochloric acid). You see at once that a bubbling commences all round the chalk. The bubbles pass up through the liquid and burst on its surface. These bubbles are really bubbles of the very gas we want to get (carbonic acid gas). They have come from the chalk. It is very easy to collect as much as we want. Let us fill these three bottles with the gas. We have only to dip the other end of the bent tube into the vessel, and the gas will at once pass into it II. ITS PROPERTIES Show the bottle of gas just collected. I have told you that these bottles are filled with carbonic acid gas. Look carefully and tell me whether you can see it. No, the bottle appears "empty," or full of nothing but air. Well, there is no air at all in them nothing but car- bonic acid gas. LES. xvn CARBONIC ACID GAS 47 What therefore can you tell me about this gas ? It is invisible. Let it next be tested for smell, and lead the class to tell that it is an inodorous gas. Now I want you to think of the way in which we collected it, by merely letting it pour into the bottles as we should water. What was there already in the bottles 1 Air. Quite right, and before any other substance could be put into them the air had to be turned out. If we had been pouring water into them, the water would have driven out the air and taken its place. Can you tell me why 1 Because the water is heavier than the air. It would have sunk to the bottom of the bottle and pushed up the air. This is just what makes it so easy for us to collect the carbonic acid gas. This gas is heavier than air, and sinks to the bottom of the bottle, pushing the air out above it. But we have had no proof yet that the bottle contains carbonic acid gas. Let us see whether we can prove it. Take bottle (No. 1) and pour into it some clear lime-water. Tell what you have done, and explain what the result will be. Now shake the bottle, and call attention to the change. The lime-water has become white and milky- looking. We know it is carbonic acid gas, because it gives clear lime-water this milky appearance. Plunge a burning taper in the next bottle. The flame is instantly extinguished. Fix a piece of burning taper at the bottom of another bottle containing only air, and pour the gas from the third bottle into it (as though it were water). The gas at once extinguishes the flame of the taper. Prove either by the lime-water test, or by again inserting a burning taper into each, that the gas has actually passed from one vessel to the other. 48 OBJECT LESSONS STAND, m " We know now that it is carbonic acid gas because it at once extinguishes a flame. What happened when we applied a lighted taper to the coal-gas 1 It took fire instantly, and burned with a bright flame. Does the carbonic acid gas burn t No, it will not burn, and it will not allow anything else to burn. III. FIRE PRODUCES CARBONIC ACID GAS Take a dean glass bottle with a narrow neck, and lower a burning taper into it. Let the children notice that after it has burned for a few minutes, the taper gradually dies out. Remove the taper and pour some dear lime-water into the bottle, and shake it up. What do we see? The lime-water has become white and milky-looking. What does this prove? That there is carbonic acid gas in the bottle. When we put the burning taper in there was nothing in the bottle but air. The carbonic acid gas has been produced by the burning of the taper. Tell that all our fires and furnaces, all our lamps for lighting, all burning of every sort, produce carbonic acid gas. Pour some dear lime-water into a tumbler and set a boy to breathe or blow air into it from the lungs, through a straw or a piece of glass tubing. Call attention to the change in the lime-water. There is the same milkiness we have seen before. What does that prove? That the air which we breathe out contains carbonic acid gas. Tell that not only we ourselves but all animals breathe out carbonic acid gas. LES. xvn CARBONIC ACID GAS 4d Lesson XVIII CAEBONIC ACID GAS I. EECAPITULATORY LEAD tfte children to describe, step by step, the properties of this gas, so far as they were dealt with in the last lesson. Make them describe the experiments by which we proved those properties. What happened when we burned the taper in the narrow-mouthed bottle 1 Carbonic acid gas was formed as the product of the burning. How did we prove that ? We used the lime-water test. The clear lime-water became cloudy or milky, thus proving that there was carbonic acid gas in the bottle. Why did the clear lime-water in the tumbler also turn cloudy when we breathed into it ? Our breath contains carbonic acid gas. It was this carbonic acid gas that acted on the lime-water and made it cloudy. II. CARBONIC ACID GAS IN THE Am The breathing of animals and the burning of fires then are constantly producing carbonic acid gas. What becomes of it ? It mingles with the air. There is always carbonic acid gas in the air. Look at this saucer. I filled it with clear lime-water early this morning. Do you notice anything particular about it? It has the same milky, cloudy look on its surface as we saw in the tumbler when we breathed into the lime-water. What does that prove 1 That carbonic acid gas has been acting on the lime-water. There was no carbonic acid gas in the saucer itself. Whence then did it come ? From the air. VOL. II E 50 OBJECT LESSONS STAND, in Notice, however, that there is only a thin film on the surface the water below is clear enough. That tells us clearly that after all there is only a very small quantity of carbonic acid in the air. III. PLANTS INHALE CARBONIC ACID GAS And yet with fires and animals always making it, we might have expected to find a very large quantity always present in the air. Let us see how this is. Show some cress growing on a piece of common flannel. It may be prepared a few days beforehand, and will grow without any trouble. First soak the seeds in water, then spread them on the flannel, and lay the flannel on a plate, taking care to have enough water in the plate to constantly keep the flannel moist. By the time it is wanted, the flannel will be covered with little plants. Where did these little plants get the food to form the materials for building up their stalks and leaves ? Not from the flannel and not from the water. They could not build up their solid parts with water. Tell that they got their materials from the air. They took in from the air all the carbonic acid gas they could get, and used this to make up their own substance. Tell also that every plant that grows takes in car- bonic acid gas from the air for the very same purpose. It is their food. This is why there is never very much carbonic acid gas in the air. As quickly as it is formed by breathing and burning, it is taken in by plants as their food. IV. ITS DANGERS Men and animals breathe out carbonic acid gas, but cannot breathe it in. It is a poisonous gas. 1. Tell of the evil of silting in a dose room. Carbonic acid LES. xix PARTS OF A PLANT 51 gas being produced, and not carried off, we breathe it, and become heavy and sleepy, and our head aches badly. 2. If we attempted to breathe carbonic acid gas alone, it would suffocate us, and we could not live more than about two minutes. 3. liefer to the explosion of fire-damp in the coal-mines which we mentioned last lesson. Tell that when an explosion takes place in a mine, much carbonic acid gas is formed. The miners call it " after- damp," or " choke-damp." Dreadful as the first danger is, more are Mled afterwards suffocated by the choke- damp, than by the explosion itself. LESSONS FKOM BOTANY Lesson XIX PAETS OF A PLANT CALL upon the children to mention some of the common plants which they see growing in the fields and gardens. Lead them to tell that each of these consists of several dis- tinct parts. What is the name which we give to the different parts of a plant ? We call them organs. Why do we call them organs'? An organ is some special part of the plant which has some special work to do. Each of these special parts of a plant has its own special work to do, or duty to perform. Hence we call them organs. Have the various organs enumerated and written on the black-board. 52 OBJECT LESSONS STAND, in II. VITAL ORGANS Lead the dass next to tell that during a certain part of the year we find the plant has only a root, stem, and leaves ; that later on it produces flowers ; and tJiat these in time produce fruit and seeds. Show a young plant in a pot a scarlet bean will do as well as any. Turn it out of the soil carefully, and show tJiat as soon as the little plant pushes its head above ground, it has the three parts or organs root, stem, leaves. As long as the plant lives, the same three organs must live too. The plant could not live without either of them. We may call them the vital organs of the plant, because they have to do with the everyday life of the plant. Explain the meaning of vital. It is these organs which feed and nourish the plant and make it grow. They are generally called the organs of growth or vegetation. III. ORGANS OF REPRODUCTION Lead the children next to think of the flowers. These do not appear till the plant is fully developed. Does it injure the plant or endanger its life if we pluck its flowers ? No, we pluck flowers from plants all through the summer, but the plants still live, and are as healthy as before. What does this prove ? That the flowers are not " vital organs," and they have nothing to do with the work of feeding and nourishing the plant. Lead the children to think of the scarlet bean, or some other familiar plant, fully developed, and bearing flowers. We do not pluck the flowers, but let them remain on the plant. What becomes of them 1 After a time they die and fall off, and leave in their place a little green thing, which LES. xx THE WORK OF THE ORGANS 53 will presently grow into a bean-pod the fruit of the plant, and this pod will contain the seeds. So then the work of the flowers is to form the fruit and the seeds from which new plants will grow. They have, in fact, to provide for the growth of new plants for the next season. We call them organs of reproduction Organs whose duty it is to reproduce new plants. Explain the term. Lesson XX THE WORK OF THE ORGANS I. THE ROOT THEN a plant out of the pot, and let the children examine its roots. The bean plant mil once more serve our purpose well. The root is that part of the plant which makes its way downwards into the soil. Notice that this plant has a long, tapering, main root, and a number of strings or fibres branching out in all directions. Let this lead up to the terms "tap-root" and "fibrous root." In some plants the tap-root is very (large and fleshy, and has no long strings. Call upon the class to name some plants of this kind. Call upon the class to tell the object of such roots. They act as a sort of storehouse for food for the plant. Such plants live during two seasons. We call them biennials. The food-supply laid up in them is to feed the plant when it wakes up after its winter sleep. Other plants have no tap-roots, but the fibres spring directly from the stem, and spread downwards and out- wards through the soil. Grass and corn have roots of this kind, and so have all plants that die down every year. We sow the seeds of such plants in the spring. Let the children mention some. 54 OBJECT LESSONS STAND, in Such plants, because they live only one year, are called annuals. They therefore require no winter storehouse. Trees and bushes have fibrous roots too, but these are thick, woody roots, and spread their branches deep into the soil. They have to supply the everyday wants of the plant for many years. Such plants are called perennials. Explain the name. Note next that the root of our scarlet runner is not green like the other parts of the plant. Wky is this 1 Explain. Make the class tell the double function of the root. It has to fix and hold the plant firmly in the soil, and to supply it with earth-food. Describe the root-hairs the actual feeders. All the food which the plant obtains from the earth has to pass up through these delicate threads. How can this be 1 Lead the children to think of the kind of food to be obtained from the soil, &uch food could not pass into the plant except in in a state of solution. Tell how the rain acts as a natural solvent for such matters. The root-hairs are very absorbent. They suck up the dissolved nourishment which the plant requires. II. THE STEM Make the children tell tJiat the stem is that part of the plant which grows upward into the air, and bears the leaves and flowers. Call upon the class to tell that most stems stand erect or upright, but that some are too weak and fragile to stand without support. Show, if possible, some specimens of climbing, twining, prostrate, and creeping stems. Let the children describe them. III. THE LEAVES The structure of the leaf should be recapitulated from the earlier lessons. See that the class are again made familiar with the terms foot-stalk, blade, ribs, veins. LES. xxi PARTS OF A FLOWER 55 Remind them that these all form channels for the upward passage of the sap the earth-food which has been taken in by the roots. The breathing-pores on the surface of the leaf should be now briefly described, and their proper name, " stomata," given. Eefer next to the recent lesson on carbonic acid. Lead the children to tell of the presence of this gas in the air ; its source ; and the reason why there is not a great accumulation of it, since it is so constantly being supplied. Plants absorb it from the air for their own support. It is by means of these stomata in the leaves that the plant is able to suck in the carbonic acid from the air. The stomata breathe it in, as it were ; and this is why we sometimes call them breathing-pores. The plant itself separates from the gas just what it wants for its own sustenance, and breathes out the rest to the air once more. The sap, as it flows, carries off what has been taken from the carbonic acid, and so the new air-food finds its way into all parts of the plant. That which is taken from the carbonic acid by the leaves is carbon a substance you knoAv best in the form of charcoal. We shall have more to say about it in a later lesson. Lesson XXI PARTS OF A FLOWER THE flowers are most important organs. They have to produce new plants, which shall live after the parent plant is dead. We call the flowers organs of reproduc- tion. I have here some well-known flowers. Who knows their name ? Wall-flowers. Quite right. Now let us see what we can find out about them. 56 OBJECT LESSONS STAND, in Take some of the flowers in your hands and try to follow me. N.B. If the season be too late for these, take some other common flower, and proceed on the same lines. L THE CALYX The outer covering of the flower that which holds it to the flower-stalk, is called the calyx. Separate it care/idly from one of the specimens, and show that it forms a sort of little cup into which the rest of the flower fits. Call upon the children to examine it for themselves, and show that the calyx consists of four separate pointed leaves. These we call sepals. Flowers differ in the number of their sepals some have more than this, some less. Tell that while the flower was only a little bud these sepals folded themselves round it, and protected it from wind, rain, and sun, till it was fit to burst open. In some flowers the sepals are joined together at their edges ; this one, as well as many others, has its sepals separate. The sepals of most flowers are green, but in some the sepals are richly coloured, e.g. the fuchsia. IL THE COROLLA Call attention to the second or inner cup of flower-leaves which rests on the calyx. This is called the corolla. It consists of four separate flower-leaves, larger than those of the calyx. Instead of being coarse and green, they are soft and velvety to the touch and richly coloured. We call these flower-leaves the petals. Remind the class that, as in the case of the sepals, the number is not always four, neither are the petals always separate. In the convolvulus the petals are joined together at their edges, so as to form a sort of funnel or bell. LES. xxi PARTS OF A FLOWER 57 These beautiful flower-leaves, although so bright and gay, . are not the most important parts of the flower. These parts are hidden away in the very centre. Tell that the petals, like the sepals, ad as a protecting cover for these inner parts of the flower while they are first forming in the bud. III. THE STAMENS Pluck the petals carefully from the flower, and show the inner circle or whorl of stamens. Here we have growing up from the bottom of the flower- cup six long slender stalks, with a little oval knob at the top of each. These are the stamens, and the little knobs are called anthers. These little knobs are really hollow cases, and are full of a fine yellow dust which we call pollen. Open some of the antJiers and show the pollen by dusting it on a sheet of paper. IV. THE PISTIL Eemove the six stamens, and show that we have now arrived at the most essential part of the flower. It stands in the very centre, surrounded by all the other parts. We call it the pistil. It consists of two parts, the ovary and the stigma. 1. The ovary. The lower part of the pistil is swollen out larger than the upper part. It forms a sort of case or box called the ovary. This ovary is the fruit of the plant. It is really the seed-vessel. It contains a number of little rounded bodies, the ovules, arranged in regular order, side by side. These little ovules will in time become seeds. If possible, get one of the forming seed-vessels of the wall- flower. This is the ovary the fruit of the plant. It was formed from the lower portion of the pistil. Split it carefully open, and show tJiat it consists of two seed- vessels. TJiese we call carpels. 58 OBJECT LESSONS STAND, in Slww the tiny ovules in both. 2. The Stigma. The upper part of the pistil is the stigma. It is of a loose, spongy nature. It sometimes rests immediately upon the top of the ovary and sometimes it is joined to the ovary by a long, slender stalk the style. Every flower has not all these four parts calyx, corolla, stamens, and pistil. Some flowers have a calyx, but no corolla, some a corolla, but no calyx. In some we find a pistil but no stamens, in others Stamens without any pistil. Which of these must be present if the flower is to produce fruit and seeds ? The pistil. Why t Because the fruit with its seed-vessels is really part of the pistil itself. Lesson XXII THE FLOWER AND ITS WORK I. INTRODUCTION LET the children recapitulate carefully the subject of last lesson. It would be very profitable and interesting to the class to call one of the boys to the front and let him dissect a simple flower before the rest, just as he has seen the teacher do it. The teacher, of course, will be on the look-out and will be ready to assist where he thinks it needful. Have the names of the various parts of the jlower calyx and sepals, corolla and petals, stamens, anthers, pollen, stigma, style, ovary, ovules, pistil written mi the black- board, with a short description. II. FUNCTION OF EACH PART Let us now trace the flower and its work from the time it is a little growing flower-bud till it withers and drops to the ground. LES. xxn THE FLOWER AND ITS WORK 59 Think of the flower-bud. What part of the flower has any work to do while the flower is in its infancy ? The flower-leaves. The calyx with its strong outer covering of sepals forms a protection against the weather. The soft, velvety petals of the corolla fold round the delicate young stamens and pistil. When stamens, anthers, and pistil are able to bear exposure, the flower-leaves open. All this time the ovary, with its ovules, has been growing, but the ovules cannot become seeds yet. Tell of the anthers filled with that yellow dust called pollen. -That dust has a most important work to do. The ovules are there in the ovary, but without the pollen they can never become seeds. The anthei-s at length become fully ripe and burst open, and of course the yellow pollen is scattered. Some of it falls on c the stigma of the pistil. What did I say about this stigma? It is loose and spongy in structure. The pollen is then caught on the broad head of the stigma, and at once forces its way through its spongy substance, until it reaches the ovary and the ovules. There it acts on the tiny ovules in a wonderful waj-, by conveying to them a little quantity of fluid which fertilises them and helps them to grow into seeds. But some flowers have a pistil with no stamens. Let us see how they fare. Tell of the bees flying about from flower to flower in search of honey. The honey is stored in a little receptacle quite at the bottom of the flower. The bee cannot get what it wants without forcing its way into the centre of the flower. As it does this it pushes aside the stamens, and probably breaks some of their anthers. What must happen then ? The bee becomes covered with the yellow pollen. The bee's next visit may be to an incomplete flower, one with no stamens. Such a flower could never produce fruit and seeds. Why? 60 OBJECT LESSONS STAND, in But what happens when the bee visits it 1 In forcing its way through to get at the honey it shakes some of the pollen from its body on to the stigma, and the fertilising work is accomplished. Tell that the flower-leaves by their gay colours help to attract the bees. Lesson XXIII SEEDS AND SEEDLINGS DICOTYLEDONS COMMENCE by making the class recapitulate briefly the stages of the growth and fertilising of the seeds from the ovules in the ovary. The seeds, when fully ripe, are stored up till next season, and if they are then put into the ground they mil become new plants. PARTS OF A SEED Illustrate with some very common seeds. Show some scarlet beans or broad beans. Let the children examine them, and tell their names. We have selected large seeds in order that we may find their parts easily; and to help us in examining them, I have had them in soak for some hours. Hand a few of the seeds round the class, and help the children to examine them for themselves. 1. The testa. The first thing to notice is the loose, wrinkled skin that covers the seed. Compare with a seed which has not been soaked. We, call this tough outer skin the testa. Call upon children to tell its use as a protecting covering for the inner kernel. Point out the long black scar along the edge of the seed. Tell that this marks the spot where the seed was attached to the ovary. LES. xxni SEEDS AND SEEDLINGS 61 It is known as the hilum. 2. The seed-leaves. Slit the testa carefully with a knife, and remove it so as to expose the inner parts of the seed. Show that the seed really consists of two pieces placed side by side. Each is a thick, solid lobe. We call these lobes the seed-leaves. Point out that these seed-leaves are not separate, but are joined together in one spot, the hilum, as by a sort of hinge. Cfy* c ] Spread them open, so that the two lobes and the hinge which joins them may be clearly seen. 3. The germ. Tell that this little hinge is the most essential part of the seed, for it is the germ of the new plant. Show its two parts one, called the plumule, pointing upwards ; the other, the radicle, pointing downwards. Have these two parts examined carefully. Point out that the plumule is really a tiny bud, which will make its way upwards through the soil, and form the stem and leaves; while the radicle will become the root. Radicle means little root. Each seed then contains in itself the germ of a little plant a tiny thing containing all the essential parts of a new plant root, stem, leaves, and only waiting an oppor- tunity to grow. Now that the parts of the bean seed have been clearly grasped, it would be well to hand round the class for similar examination smaller seeds of the same kind, commencing with a few peas, acorns, almonds, the kernels from plum and cherry stones, and so passing on to apple pips, and even some of the very small seeds of our common garden flowers. It cannot fail to interest the child to see that he is able to find exactly the same parts in these little seeds as in the large seeds which have been previously examined. A few simple questions will suffice to fix all these facts in the memory. How do all these seeds resemble one another 1 They all have two lobes or seed-leaves which are joined together at the hilum by a sort of hinge. 62 OBJECT LESSONS STAND, in What is this hinge 1 The germ of a new plant. Of what does it consist ? What is the meaning of the word " radicle " ? What becomes of each part of the germ 1 The great point to remember about all these seeds is that they have two thick lobes or seed-leaves. Nearly all the plants which we see in the fields and gardens come from seeds with two seed-leaves. I want you to try and remember a hard word which means this. Let us write it on the black-board " di " means " two," and " cotyledon " means seed-leaf. This name, dicotyledon, is given to all seeds which have two seed-leaves, and it is also given to the plants which come from such seeds. All the seeds we have examined are dicotyledons, because they have two seed-leaves, and we could easily pick out other seeds of the same class by examination. Now I want to tell you how you may know the plants themselves when you see them growing, and when there are no seeds to tell the tale. Refer to the lesson on leaves. Lead the children to tell the great distinction between the leaves of one plant and those of another. One plant bears net- veined leaves, the other parallel-veined leaves. Tell that all plants which bear net-veined leaves grow from seeds with double seed-leaves, like those we have examined. They are dicotyledons. Lesson XXIV HOW SEEDS GROW I. GERMINATION OUR work in this lesson is to learn how the tiny germ in the seed grows and becomes a real plant. This is what I mean by germination. LES. xxiv HOW SEEDS GROW 63 Show a few bean seeds which have been placed in flower-pots under favourable conditions of warmth and moisture. It would be advisable to present them in various stages of growth. To secure this, they should have been set at intervals varying from a month to a few days before the lesson. Commence with the most recent ones, and let the children tell what they observe. The first effect of the moisture is to cause the outer skin or testa to swell and wrinkle up until at last it bursts. Show some that have just burst open. Tell that while this has been going on, the warmth and moisture together have made the tiny germ wake up as it were from its long deep and stretch itself out. Explain that until now it has actually been in a sort of sleep alive, but showing no signs of life. The splitting of the testa takes place just when the germ is trying to force its way out; for as soon as it wakes up from its sleep, it begins to grow, and wants more room. Show some other specimens of the growing plantlets, and let the children see for themselves the gradual development of the parts upwards and downwards. Let them trace the radicle in successive plants at first only a simple tap-roo't, very small, and forcing its way down- wards into the soil ; then gradually sending off (as it increases in size) tiny branches or rootlets all round. It will in time become a large fibrous root. Follow the development of the rest of the germ next. Show one specimen with the seed-leaves just expanding, and the plumule forcing its way upwards between them. Pass then to another with the seed-leaves just making their way above ground, and the growing bud of the plumule already in the act of bursting into leaf, and so on. II. THE WORK OF THE SEED-LEAVES Lead the children to think of a hen's egg. Why does the hen lay the eggs ? To produce little chickens. 64 OBJECT LESSONS STAND, in Tell that in each egg there is a tiny germ which will grow into a little chicken under proper conditions of warmth. The hen supplies the warmth by sitting on the eggs, and in due time they are hatched and the young chicks come out, fully formed, and able to run about, and pick up food for themselves. Compare the size of the tiny germ with that of the newly- hatched chicken. The germ has been growing ever since the hatching began. Tell that the egg contains not only the germ of the little bird, but also a sufficient store of exactly the kind of food it requires to make it grow, until it is able to break the shell and come out to pick up food for itself. Now carefully show the analogy between the egg and our seeds. We have seen the germ, which grows at last into a real plant. This plant will have roots and leaves, and will be able to seek its own food by and by. The seed-leaves contain a store of food just of the proper kind, and of a sufficient quantity to last the little plant until the root and leaves are quite ready to seek plant-food for themselves. As soon as this is the case, the seed-leaves wither and drop off. Lesson XXV SEEDS AND SEEDLINGS MONOCOTYLEDONS As an introduction to what is now to follow, lead the children to tell briefly the main facts taught last lesson. What name do we give to all seeds like those we last examined 1 Dicotyledons. What does that mean ? How can we tell a dicotyledonous plant without seeing its seeds ? LES. xxv SEEDS AND SEEDLINGS 65 What other parts are there in a seed besides the seed- leaves ? What is the most important part of a seed ? Of what does this germ consist ? How does the plumule develop itself ? What becomes of the radicle ? What enables the germ to grow into an actual plant in this way ? Whence is the plant-food obtained 1 When do the seed-leaves cease to feed the plant ? What becomes of them ? Now show a few grains of wheat and Indian corn, and let the children tell what they are. We are going to learn some- thing about these. As both are alike in structure, we will examine the Indian corn because it is larger. I. THE PARTS OF A GRAIN OF CORN Show some grains of Indian corn that have been in soak for a few days. Tell the object of so soaking them. The grains in their natural state are hard and brittle ; we could not cut them. With a thin, sharp knife cut through one of the grains lengthwise, from top to bottom, so as to divide it into two broad, flat halves. Let the children examine these two sections. What do we see? The knife has cut through some- thing in the centre quite different from the rest of the grain. Let us take away the two halves of this central part. All the rest of the grain in which that was placed is of one character. It is simply a mass of matter which has become somewhat soft through the soaking, but in the dry state is very hard and brittle. The corn grain is in reality not merely a seed, it is an actual fruit, and it was the seed itself which we found embedded in the centre of the grain. 1. The seed. Take next- another of the soaked grains, and VOL. II F 66 OBJECT LESSONS STAND, in carefully remove with the knife all the outer mass of soft sub- stance, so as to leave the entire seed free. Let the children examine it, and point out that, like other seeds, it has the two essential parts the plumule and the radicle. These are the germ of the new plant. Next call attention to the outer part of the seed. This outer part is all in one piece, and folds itself completely round the rest of the seed (the plumule and the radicle) as if to protect it. How were the plumule and the radicle of our other seeds protected ? They were enfolded by two seed-leaves. Open a soaked lean seed and show the arrangement again. Now I want you to remember that in the corn grain we have the same arrangement, with one difference. What do you think this part is that folds itself round the germ ? The seed-leaf. Then what is the difference between the bean seed and the seed in the corn grain ? The bean has two seed- leaves ; the corn grain only one. It is this one seed-leaf which envelops the germ. See, I will spread it out as far as it will go. It is all in one piece. You must try to remember the name which is given to seeds of this kind, as well as to the plants which grow from them. Let us, as before, write it on the black-board. The name is monocotyledon. The first part, "mono," comes from a word meaning "one," and "cotyledon" means " seed-leaf." Monocotyledons, then, are seeds which have only a single seed-leaf. Now think for a moment about our other seeds the dicotyledons. Suppose we want to find out from the growing plant itself whether it is a dicotyledon or not, what part of the plant do we examine t The leaves. How do we find from the leaves what we wish to know ? Plants which grow from dicotyledonous seeds have net-veined leaves. IKS. xxv SEEDS AND SEEDLINGS 67 Now remember that plants which grow from seeds with one seed-leaf (i.e. monocotyledons) bear parallel- veined leaves. So that the leaves again in this case will tell us what we wish to know. We know now that Indian corn is one of the mono- cotyledons. Wheat, barley, oats, rye, rice, and millet are also plants of this same kind. We call them the corn grasses. The sugar-cane and the useful bamboo are also monocotyledons. Refer the class to some of iheir old lessons, and make them tell the connection between these plants, the ordinary grass of the meadow, and the many varieties of ornamental grasses in our gardens. They are all of the same class. Show some common grass seed. These are monocotyle- dons, and if we could examine them we should find them very similar to the large grains which we have examined. 2. The grain. The whole of the grain in which the germ is embedded is simply a store of plant-food which the parent plant has laid up in the grain to feed the tiny plantlet. Where is this plant-food stored in the case of the di- cotyledons ? In the two thick, solid seed-leaves. In the monocotyledons the seed-leaf is not thick and solid. It is not meant as a storehouse of food for the little plant. That food is laid up, not in the seed-leaf, nor in any part of the plantlet itself, but in the mass of matter outside it with which the grain is filled. In the dicotyledons the germ with its two seed-leaves takes up the whole of the space within the husk or testa. Show the difference in the case of the monocotyledons. In these the germ is very small indeed ; its store of food is outside itself. II. GERMINATION Tell that in these seeds there is exactly the same awakening and springing into life under the influence of warmth and moisture as we saw in the dicotyledons. 68 OBJECT LESSONS STAND, in The moisture changes the solid mass of plant-food in the grain, all round the little germ, into a watery sap which is greedily absorbed by the radicle. It is upon this food that the little plant lives and grows until it is able to get its own food from the soil This it has to do very early, and, in order to provide itself with the necessary means to do so, it sends out from the radicle a whole cluster of fibrous roots at once, instead of commencing with a tap-root as the dicotyledons do. Lesson XXVI THE BARK SHOW a picture of one of our familiar trees. Call attention to the rough, gnarled appearance of its stem and branches. Show next a piece of the actual stem of some tree, with special reference, as before, to the rough outside. This rough outside part is quite different from the rest of the woody stem. It forms an outer coat for the tree. Strip off a piece of it so as to show the outer coat with the wood beneath. It is this outer coat which gives the tree such a rough appearance. Who knows what name we give to this outside coat of the tree ? We call it the bark. Illustrate further with the stem of some well-known plant, e.g. a common cabbage-stalk, and show that this outer coat or bark is not confined to trees. It is a sort of skin that covers the external parts of all plants, just as the skin covers our bodies, although we become most familiar with it in the woody parts of trees. The bark acts as a sort of protecting covering for the plant against the changes of the weather. The bark is really a double coat, for there is an inner coating beneath this rough one on the outside. LES. xxvi THE BARK 69 I. THE OUTER BARK This is the tree's greatcoat, and is, of course, thicker and coarser than the one beneath it. In some plants it becomes very thick and corky. Show, if possible, some specimens of trees with thick lark. The cork which we use for so many useful purposes is the outer bark of a kind of oak tree which grows in Spain. These trees are grown specially for their bark, which is stripped off them from time to time. The bark of the oak, larch, chestnut, willow, birch, and other trees is used largely in the manufacture of leather. The bark, when ground small and steeped in water, makes a liquor called OOZ6, which is rich in tannin, a substance which is able to convert the hides into real leather. The outer bark of certain trees is used in dyeing ; and the valuable medicine quinine is made from the bark of the cinchona tree. II. THE INNER BARK Show some twigs of the common lime tree. Strip off its outer coat so that the children may see the inner layer beneath. Let them examine this. Help them to remove some of it. What is the nature of this under coat? It has a fibrous or stringy appearance. Show some common bass or bast, such as is used for pack- ing furniture, and for various purposes in the garden. Tell its name, and explain that it is really the inner bark of this very tree the lime tree. Hand some of it round for the children to examine. Call atten- tion to its thin, delicate structure. It is no thicker than paper. Tell that there was a time (before people learned how to make paper) when the thin layers of this inner bark were used to write upon. This is why we sometimes hear it called by another name liber. Liber means a book. Next show that although it is a very easy matter to split or 70 OBJECT LESSONS STAND, in tear the bass asunder lengthwise (that is, in a line with its fibres) it is not so easy to break the fibres themselves. Let the children try and break a piece by pulling it. They find it very tough and strong. Show at the same time how easily it can be bent or twisted. It is very pliant. Tell that these properties of the bass make it very useful to us. Although, properly speaking, the name bass is confined to the inner bark of the lime tree, we commonly apply the name to the inner bark of many other plants. Lesson XXVII KINDS OF BASS I. THE BASS OF THE LIME TREE THE people of Russia make great use of this substance for ropes, mats, shoes, hats, and various other things. Lead the children to tell that its peculiar properties make it specially adapted for such purposes. For example, it twists readily into a rope, and when twisted it is very tenacious and strong, and will not easily break. The Russians not only make enough of these things for their own use, but they send them to other countries. We receive from them every year no less than four million bass mats, which we use in packing furniture, covering up young plants in winter-time, and in many other ways. II. FLAX Show a picture of the growing flax, and, if possible, one of the stalks of an actual plant. Tell that it grows in the fields like corn and other crops. It grows from two to three feet high, and bears pretty blue flowers at the top of its long slender stalks. When LES. xxvn KINDS OF BASS 71 the flower dies off, it leaves behind a pod or seed-vessel, full of little flat, oval seeds. Show some of the seeds and tell their name linseed. Explain that linum is Latin for flax. Hence the name linseed, which simply means flax seed. This linseed is useful in many -ways. Pressed in a mill, it gives out a valuable oil (linseed-oil), and the solid portion left behind in the mill is oil-cake, which we use for feeding cattle. In some countries the flax plant is grown chiefly for its seeds, for the sake of the oil and oil-cake they yield. But it is generally grown for a more important purpose. The most valuable part of the plant is its stalk, for from the inner bark of its stalk we make linen. Show a piece of linen, and let the class tell its name. Lead them to tell the reason for the name, and the connection between linen, linseed, and linum. Tell that in warm countries the plants produce the best seeds, but that those plants which are wanted for their stalks are grown best in temperate climates like our own. III. HEMP The hemp plant is very like the common nettle. It is grown in many parts of the world, and, like flax, is chiefly useful for its stem. We use the strong tough fibres of its inner bark to make rope, twine, and cordage, canvas, sail-cloth, and sacking, and other coarse but strong materials. Its seeds yield oil and oil -cake when pressed in a mill. We use them for feeding birds. Show some of the seed. IV. JUTE Show a specimen. The plant that yields this substance grows chiefly in India. As in the flax and hemp plants, the most valuable 72 OBJECT LESSONS STAND, in part is the stem. The inner bark of the stem produces the substance we call jute. Its fibres, although not so strong and tough as those of flax and hemp, have a smooth, glossy appearance. It is very cheap, and easily worked. The chief use of jute in this country is for making sacking. It is also used to make sheeting, mats, and carpets. We frequently use it mixed with flax and hemp to add to its strength. Lesson XXVIII FLAX COMMENCE by making the class recapitulate such fads from Uic last lesson as will lead up to what follows. Let them describe the flax plant with its long slender stalks and brigM blue flowers its fibrous inner bark, and the use we make of it the name we give to the fabric made from it, and why the other product of the plant which is valuable, and the uses to which we put it the difference in tlie plant when grown in a warm and in a temperate climate, and so on. I. CULTIVATION OF THE PLANT Our climate is well adapted for the growth of flax for linen-making. In the north of Ireland it is extensively grown, and we import large quantities from Belgium, Holland, and Russia, that from Belgium being the best in quality. The plant is an annual, easy of cultivation. It is sown in the spring, and is ready for gathering in July. The Hax-field can therefore be used for other crops before the next winter comes. As the plants are wanted, not so much for their seeds as for their fibrous Stems, the farmer does nob wait till they are quite ripe before gathering them. LES. xxvni FLAX 73 When the plants are fit for gathering, their leaves fall off, their stems begin to turn yellow, and the seed-pods to become brown. Men, women, and children are then sent to uproot the plants by hand. The plants are all pulled separately, carefully dried in the sun, and then laid in order, crossing each other, with the root-ends pointing one way. II. FLAX-DRESSING The flax, as pulled from the field, needs a great deal to be done to it before it is fit for the manufacturer. 1. Rippling. The object of this process is to separate the seed-pods from the stalks. A coarse iron comb is fixed perpendicularly on a block of wood, teeth uppermost. This is known as a ripple. Men, called ripplers, take the dried plants one by one from the stack, and draw the stalks through the teeth of the ripple. The seed-pods too large to pass between the teeth fall on one side, and are received on a cloth. They are carried away and dried, after which they are either ready for next year's sowing, or to be pressed for the oil and oil-cake they yield. The rippled stalks are bound together In bundles. 2. Retting. The object of this process is to separate the bast fibres from the woody part of the stem. This is done in various ways. Commonly, the stalks are steeped, root downwards, in a shallow pool until partially rotted. The process is known as rotting or retting. They are usually kept in the water ten or twelve days, and by that time the fibres become loosened and separate readily from one another. NOTE. This rotting or loosening process does not affect the fibres. It simply dissolves the gummy, pulpy matter of the stem. The flax in this state is taken out of the water and left 74 OBJECT LESSONS STAND, m to drain, after which it is tied in bundles, and spread out evenly to dry. Illustrate all this process with a common cabbage-stalk. Soak for some time previously, and beat with a hammer, so as to show the fibres and soft pulpy matter of the stem. 3. Breaking and scutching. The next business is to break in pieces the hard woody portion of the stem, which the steeping has made very brittle, and separate it out from the fibres. This is done in various ways. The flax, freed from woody and other matters, is tied up into bundles of from 16 to 24 Ibs. each, and is ready for the manufacturer. Lesson XXIX LINEN-MAKING SHOW, if possible, a stick of the scutched fibres. Point out that the fibres are of different quality in different parts of the stem. Those nearest the root are coarse and strong ; those in the middle, finer ; and those at the top, very fine but not very strong. The first business to be done at the flax-mill is therefore to cut the fibres into three lengths, and keep them separate for special kinds of fabrics. I. HECKLING The heckle is a sort of comb with steel teeth. It is set upright in a wooden frame. A man, called the heckler, draws the flax through this comb repeatedly, first using a coarse then a fine heckle. The object is to straighten the fibres and arrange them side by side. It also cleanses the fibres of dust. The combed and straightened fibres are called line. These form the material for linen-making. The coarse combings of broken fibre are called tow. This is used in the manufacture of rough fabrics. I.ES. xxix LINEN-MAKING 75 The heckling process causes great waste. Out of 100 Ibs. of scutched flax, not more than 50 Ibs. of line is produced. In most of the great mills nowadays this heckling process is done entirely by machinery. Show, if possible, a bundle of this heckled line, and let the children examine it, and note its properties for themselves. The fibres, although fine and soft to the touch, are very tenacious. They do not easily break. They have a glistening, silvery appearance, not unlike silk, and are of a pale yellow colour. The heckled line is now ready to be made up into actual fabrics. Show some pieces of fine linen, diaper, duck, huckaback, damask, sheeting. Tliese are some of the fabrics made of flax. Compare these fabrics with the heckled line. Pull a piece of linen apart, showing that the cloth is made of threads that cross each other at right angles. II. SPINNING What is there to be noticed about these threads different from the heckled line? They seem to be twisted. Tell and show that they are really twisted. The operation of twisting the fibres into thread is known as spinning. The spun thread is flax yarn. III. WEAVING THE YARN The making of the yarn into linen cloth is called weaving. Illustrate by the work of darning. Explain the terms warp and woof. Show by a picture or sketch on black-board how the two sets of threads interlace. Tell the use of the shuttle. Show one if possible. It would take too long to pass the shuttle under and over every other thread. Tell that the alternate threads of the warp i 76 OBJECT LESSONS STAND, in are all raised and lowered together, and that the shuttle, with its woof, passes first under and then over them. Tell how rapidly the weaver works his loom. But nearly all the weaving is now done by machinery. Tell that all articles made by weaving threads together into a web are called textile fabrics. " Textile " is from the Latin for " woven," and a "fabric " is any article produced by a skilled workman. Let the children name some other textile fabrics, e.g. doth, flannel, blankets, from wool ; silk and satin, from the thread spun by the silk-worm ; and calico, from cotton. LESSONS FROM ZOOLOGY Lesson XXX BIRDS AND THEIR COVERING I. INTRODUCTION INTRODUCE the lesson by leading the children to tell some of tlie points of difference between birds and the other animals dealt with in former lessons. First as to their covering. The cat, dog, sheep, cow, and rabbit have different kinds of coats. But how are all birds clothed ? All birds have feathers. Secondly, all those animals and many more besides suckle their young with milk from their own bodies. All have seen the cat suckle her little kittens. Now who has seen a mother-bird and her young ones ? Does she suckle them ? No, birds do not suckle their young. Deduce that the young ones are hatcJied from eggs which the mother-bird lays, and that from the first the parent-birds feed them with solid food. Show a picture of a nest of young birds with the old ones feeding them with worms and such-like food. LES. xxx BIRDS AND THEIR COVERING 77 .Again, all the animals we have studied live and move about either on or under the earth. What can you tell me about birds ? Birds fly in the air ; they have wings. Tell that there are other points of difference which we shall deal with as we proceed. These will be sufficient for the present. II. KINDS OF FEATHERS ON THE BIRD'S BODY Birds are clothed with feathers, the lightest, warmest, and most beautiful of all coverings. The feathers on the bird's body are not all alike. Show a bird of some sort. 1. Spread out the wings and tail, so as to show their long feathers. These we call the quill-feathers. The bird makes use of them in flying. 2. Call attention to the smaller feathers which cover the whole of the body. These we call clothing feathers. Run the fingers along them the wrong way, and then smooth them back to their proper position, and notice how beautifully they are arranged, one overlapping the other so as to form a close-fitting coat. 3. Beneath these clothing feathers, and next to the skin, are some very small, soft, fluffy feathers. These are called down. There are some big birds to be seen in shops at Christmas-time. These have a very thick, close covering of down. What birds do I mean 1 Ducks and geese. Lead the children to tell that these birds spend much of their time during all seasons of the year in the water. This close-fitting under-jacket of down is meant as a special protection against cold. III. USE OF FEATHERS 1. The clothing or body feathers of birds, especially of poultry-birds and wild fowl, are largely used for stuffing 78 OBJECT LESSONS STAND, in beds, pillows, and cushions. These birds are killed tfor food, and the feathers are plucked from their dead bodies. Lead the children to think of the immense number of such birds that are eaten in one year only in London or any other large town. In addition to the feathers obtained in this way, we every year import from other countries upwards of a thousand tons of these stuffing feathers. They require little preparation except drying and beating to remove dust? and baking in an oven to kill any vermin they may have. 2. Down, the soft, fluffy under-feathers of water-birds, is highly valued. The best down is obtained from the eider-duck and the swan. The eider-duck is a native of Iceland and Norway. As the bird itself is not used as -food, the down has to be obtained in a very curious way. The mother-bird makes her nest in the spring, lining it with down from her own breast ; and in this nest she begins to lay her eggs. Day after day men go round to take away some of the down and some of the eggs. The bird then plucks more down from her breast, and lays more eggs in the nest, only to have it robbed as before, and so on, until she can spare no more. Lesson XXXI A FEATHER I. PARTS OF A FEATHER HAND a few quill-feathers round the class for examination, and lead the children to point out the various parts, the teacher giving each its proper name. 1. The quill. This is the main stem of the LES. xxxi A FEATHER 79 fe ; ither. Its root is fixed in the skin of the bird, just as the hairs are fixed in the skin of our bodies. Cut one of them across with a sharp knife. Let the children examine, and tell that it is really a rounded, hollow tube. Let the children try to cut their quills. They find it is not such an easy matter as it seems, for although the quill is very thin and light, it is made of a very strong, tough, horny sub- stance. Test another in various ways to show that they will bear a good deal of rough usage without breaking. When lent or twisted they spring lack to their original shape. They are elastic. 2. The shaft. This is the continuation of the quill to the tip of the feather. It is made of the same tough, light, horny, and elastic substance as the quill. Show that it has four sides the upper and under sides smooth and more or less glossy, the other two sending off the long slender barbs right and left. Strip one of the feathers and show that it is so. Cut open a shaft and point out that, instead of being hollow like the quill, it is filled with a peculiar, light, tough, white substance, the pith. 3. The web. Show next the long, narrow, flat pieces or leaves which spring from loth sides of the shaft. Call attention to their long, tapering form. Pluck one or two from the feather. We call them barbs. Let the children see how they are arranged with their flat sides close together. Show that they always point towards the tip of the feather and away from the quill. Run the finger along the feather the wrong way, and show the larls ruffled up ; then draw it up the feather towards the tip, and show that the larls at once dose together again and the feather is as smooth as before. Explain that this arrangement of the larls is not acci- dental. It is a wise design to keep the bird warm, and to assist it in its flight. 80 OBJECT LESSONS . STAND, in All the feathers on the body of the bird, for the same purpose, point backwards. Thus, as the bird moves through the air, its feathers are pressed closely to its body, and the barbs of each feather are pressed close together, all pointing in the same direction. Show haw great an assistance this is to the bird in its flight. Each barb is furnished at both edges with an immense number of slender projecting fibres. These are called barbules. Explain the meaning of the words barb, barbule. The barbules are really little hooks, and it is their business to interlock themselves with each other and so hold the barbs of the web close together. When the feather is ruffled up and the barbules separated, these hooks are pulled asunder. II. USE OF FEATHERS (a) Quill pens. Slww a quill pen, some quill nibs, and an ordinary goose quill. The goose and swan are almost the only birds whose feathers are used for this purpose, although the crow quill is sometimes used for fine delicate drawing. Only the largest of the wing-feathers are used for pens. The quills cut more easily when soaked in warm water. They are hard and brittle when cold. (6) Feathers fof ornament. Tell of the use ladies make of the feathers of various birds for adorning their hats and bonnets. Few either know or think of the cruelties practised, or the slaughter carried on against the most beautiful of the feathered race in order to provide their personal ornament. Tell of ostrich farms in Africa where tJie feathers are regularly plucked from living birds. LES. xxxn BIRDS 81 I Lesson XXXII BIRDS I. BIRDS HAVE HOLLOW BONES THINK for a moment over what we learnt last lesson about the covering of birds. Why would not a fur coat or a thick hide do as well as feathers ? Feathers make the lightest of all dresses. Why is lightness necessary ? Because the bird has to raise itself in the air and fly. Then if lightness is necessary in the clothing, it is probably quite as necessary in other parts of the bird. Let us see. Show a picture of the bony skeleton of a bird ; or better still, an actual specimen if it can be obtained. If we look at the bones we shall see that they appear to be quite as large as those of any other animal the same size. But if we could weigh the bones of such an animal with those of the bird, we should find a great difference. The bones of the bird are very much lighter. Now how can this be ? Tell that the bones of the bird are all hollow. Strength rather than lightness is the main thing necessary in the bones of other animals. They have not only to support their heavy bodies, but also to provide means of locomotion. Hence their bones are thick and solid, except the hollow bones of the limbs, and they are filled with marrow. The bones of birds, however, are not only hollow, but they are very light and very thin. II. WINGS INSTEAD OF FORE-LEGS The animals we have already studied have two pairs of limbs fore-legs and hind-legs. VOL. II G 82 OBJECT LESSONS STAND, m Show that man himself is formed on this same principle, and that practically the bird is built on the very same plan, except that it has wings instead of arms or fore-legs. The bones of the bird's fore-limbs are not quite the same as those of other animals, although we can easily distinguish the different parts. . There are the upper arm, the fore -arm, and the hand ; but each of these is somewhat altered in form to serve the purposes of a wing. Now notice the broad flat bone in front of the bird's body, the one which has a deep keel projecting outwards from it. This is the breast -bone. It is large and broad, because all the great muscles which move the wings in the act of flight are attached to it. III. BEAKS INSTEAD OF MOUTHS Show some pictures of the heads of birds. Now look at these pictures and try to think of one other point in which birds differ from other animals. All birds have .hard, horny beaks or bills. "What do you know about their teeth ? Birds have no teeth. If you look again at the heads in the picture, and compare them one with another, you will see that they are not all alike. Lead the children to think of the cat, the horse, the sheep, the rabbit ; and to tell from what they have already learned, that when we want to find out the habits and food of any of these animals we examine its teeth. Birds have no teeth for us to examine, and yet we shall presently do just the same with them as with other animals. We shall examine their beaks. They will tell us all we want to know. IV. CLAWS FOR FEET Show a picture of the feet of various birds. They are LES. xxxin CLASSES OF BIRDS 83 totally different from the feet of any of the animals we have already examined. They are all claws. Remind the children that in dealing with other animals we found the feet to be quite as important as the teeth in helping us to decide the individual habits and nature of the animal. We never find the foot of a horse and the mouth of a lion, or the foot of a rabbit and the mouth of a sheep, in the same animal. It is just the same with birds. Although all birds have claws, we shall presently learn that there are many points of difference between the claws of one bird and those of another. In every case the nature, habits, and food of the particular bird depend upon the form of the claws as well as upon the structure of the bill. Lesson XXXIII CLASSES OF BIRDS I. BIRDS OF PREY LET us commence with this one. Notice the strong- looking, hooked, and pointed beak. Such a beak seems exactly suited to the piercing eyes, and the fierce, cruel-looking face of the bird. The bird is as fierce as it looks. It lives on the flesh of Other animals, and its strong, pointed, hooked beak is just suited to the work of tearing them to pieces. We call birds of this class seizers or birds of prey. They are the lions and tigers of the air. The one before us is an eagle ; it preys upon lambs, hares, grouse, and other small animals. It is found in many parts of the world, but only in the northern parts of our own island. Vultures, hawks, and owls are other birds of prey. 84 OBJECT LESSONS STAND, m II. FISHING BIRDS Now turn to this one with the long, slender, pointed bill. This bird lives either in marshy, swampy places, or by the banks of rivers, and feeds on fish, frogs, and other water animals. It is a most clever fisher, and very keen of sight. Its quick eyes no sooner see its prey in the water than it darts like lightning upon it, and the sharp, pointed beak pierces it through and brings it to the surface. Show a picture of the heron, the stork, and the crane, as illustrations of these birds. HI. BORING BIRDS This next is a picture of a bird called the wood- pecker. It has a long, straight, pointed beak very hard and strong. Let us see what work this beak is meant to do. The woodpecker lives in the trees, and feeds on worms, grubs, and insects which eat their way through the bark and often through the woody part of the tree too. Show a piece of worm-eaten wood. The bird, although it cannot see its prey beneath the bark, knows by instinct where they are. It appears to find them out by tapping on the bark with its beak, and then listening. No sooner is it sure of finding its prey than it begins to bore through the bark with its strong beak until it comes upon the spot where they are. Lead t)ie children next to see that a long, pointed beak would not be the most convenient means of capturing a number of tiny worms all wriggling to get off out of danger. Tell now about the woodpecker's tongue, the most wonderful contrivance of all. It is long, narrow, and pointed, with a sort of barbed LES. xxxin CLASSES OF BIRDS 85 tip, and the bird is able to thrust it out suddenly a long way beyond the beak. When, therefore, the strong beak has made the hole in the tree, and exposed the insects in it, the tongue instantly darts forward and seizes them before they can escape. IV. FLAT-BILLED BIRDS Here is another head. You know it, of course. It is a duck's head. Lead the class to notice the broad, flat bill, different from any of those we have seen. Show an actual head if possible. Point out tliat the bill is not hard, like those we have examined. It can be bent with the fingers. It cannot, therefore, be meant for tearing flesh, for boring holes, nor for stabbing. Open the mandibles, and call attention to the fringe on the edges of the upper one. Show the tongue. It is large and fleshy, filling the whole of the mouth, and its edges are also furnished with fringes like those of the beak. Now what is ihe object of this arrangement ? Deduce that these birds are fond of groping in the mud for worms and insects with their shovel-like bills. The mud and dirty water run out at the sides, but the insects and grubs are caught within their fringed mouths as in a trap. They live on grubs like the woodpecker, but catch them in a different way. Geese and swans belong to this class. V. NUT-CRACKING BILLS Look at this picture, and tell me the name of this bird. It is a parrot. It has a short, strong, hooked bill with a sharp point. It lives on nuts, fruits, and berries, and uses its strong bill as its nut-crackers. It also uses its bill in climbing the trees. 86 OBJECT LESSONS STAND, in VI. SEED-EATING BIRDS Show a picture of a crow or a sparrow. The beak is short, hard, and strong, and shaped like a cone. Let the children tell of some of the birds they see in cages. They are fed on hard seeds. The birds use their bills to crack the husks of the seeds. Lesson XXXIV BIRDS LEGS AND FEET I. SEIZERS, OR BIRDS OF PREY LET us commence with this large, powerful-looking claw in the centre of the picture. This belongs to the bird of prey. There are three toes before and one behind. Notice the long, sharp, hooked talons. Lead (he children to see that they are just the kind of feet we should have expected to find in connection with the cruel- looking beak of the bird. Birds of this kind pounce down suddenly with great force upon their prey, burying the sharp, hooked talons in their flesh. With their powerful wings they then raise themselves in the air, and bear off the victim to their nest to devour it, tearing it to pieces with beak and talon. Now tell me why we call them seizers ? They seize their prey, and carry it off in their talons. II. PERCHING BIRDS Now let us look at this one a claw, with three long, jointed, slender toes in front and a short one behind. This is the kind of foot we find in the sparrow, thrush, LES. xxxiv BIRDS LEGS AND FEET 87 lark, linnet, robin, and the host of little birds to be met with in our fields and woods. You have all seen a sparrow on the ground. Who can tell me how it moves about ? It goes with little short hops. It cannot walk on the ground. Its long, slender toes are made for grasping a branch or a twig, and not for walking on a flat surface. Birds of this class live almost entirely in the trees, hopping from twig to twig. They sit or perch on the branches, and are hence called perchers. They even sleep in this position, and without the slightest fear of falling. The strangest thing of all is that they could not fall from the perch if they wished. Let us see how this is. I have here the leg and foot of a fowl. Look at this glistening, white, flat cord which I can draw out at the upper part of the leg. It is very tough, Strong, and inelastic. What happens when I pull it ? The toes close up. Now I let go, and you see the toes stretch themselves out again. Explain that this strong cord passes up the leg and over the front of the knee-joint to the great muscle of the thigh. Show tJiat in the act of sitting, the bird must bend the knee-joint which pulls up the cord, and so draws the toes of the feet together without any effort of the bird itself. When, therefore, the bird perches on a branch, the whole weight of its body is resting on its legs, and this keeps the knee bent. The instant the knee bends, the^ toes draw themselves up so as to clasp the branch, and they cannot unclasp it until the bird raises itself from its perching position. The arrangement is very similar in the claws of the seizers. When the bird pounces on its prey, and flies off with it, it naturally draws it up as close to its own body as possible to assist the flight. 88 OBJECT LESSONS STAND, in This drawing up bends the knee-joint, pulls the cord, and makes the talons close together in the flesh of the victim. III. CLIMBING BIRDS The next picture we have to notice is that of a foot with two toes in front and two behind. This is the foot of a climbing bird. The parrot and the WOOd- pecker are the best examples of this class of birds. Such birds are never seen on the ground. They could only hobble about awkwardly on a flat surface. They live in the trees, their food is in the trees, and in the trees they are extremely nimble. The parrot is assisted in its climbing by its hooked beak. It uses its beak as much as its claws in clasping the branches. The woodpecker has to trust to its claws alone, but it runs very nimbly up the rough bark of the trees. IV. SCRATCHING BIRDS Let us next take this one with the strong-looking legs, and short, thick toes armed with strong, blunt claws. Such feet must be meant for hard work. Refer to the fowls in the garden, or on an ash-heap. What are they doing ? They are scratching in the ground. Why are they doing this ? Their feet are given them for the purpose of scratching in the ground in search of food. We call them scratchers. Fowls, pigeons, turkeys, pheasants, and part- ridges are scratchers. V. WADING BIRDS Look at this long and slender leg and foot. It belongs to a bird which lives near the water, and whose food is in the water. Here is a picture of the bird itself. LES. xxxiv BIRDS LEGS AND FEET 89 Do you remember the long, sharp, pointed bill ? What is that for t To catch fish. Quite right, and the long, Stilt-like legs are to enable the bird to walk or wade in the water in search of its prey. We call these birds waders. Note the long necks, and ask their object. The heron, crane, and stork belong to the waders. VI. SWIMMING BIRDS The next one is a peculiar-looking foot, with a skin or web stretching between the toes. We call it a webbed foot. Look at it and tell me whether you have ever seen a bird with such a foot. Ducks, geese, and swans have webbed feet. Show the duck's foot, and tell that such feet are specially adapted for swimming. These birds, as we saw in the last lesson, spend most of their time in the water, and get their food out of the water. Their webbed feet enable them to swim. VII. KUNNING BIRDS Show a picture of an ostrich. Tell of its great size and bulk, and note the comparative shortness of its wings. This bird never flies. It runs with great rapidity. Note the long, powerful legs. It does not swim, it does not perch. It has no need of long, wide-spreading toes or webbed feet. It has only two short thick toes which point to the front, and form a solid support for the runner. 90 OBJECT LESSONS STAND, in Lesson XXXV REPTILES I. INTRODUCTION Snow a picture of the common snake, and take this as the type of the class of animals next to be studied. Let the children describe its general appearance its oval head, elongated body tapering downwards to a long, pointed tail the entire absence of legs the peculiar covering of overlapping scales. Lead them to imagine what would be the condition of any of the animals we have already studied without their limbs. Their trunks would lie about helpless and unable to move. Here, however, we have an animal in its natural state without the least sign of a limb, and yet it is far from being a sluggish, helpless creature. The kind of snake represented in the picture lives on frogs, mice, and other small animals, and it must be quick in its movements to catch these nimble little creatures. Some kinds live in the trees, and feed upon squirrels, birds, and even monkeys. They climb the trees, and dart from branch to branch so rapidly that even these creatures cannot escape them. Birds, as we have seen, climb trees using their claws and bills, monkeys with the aid of their hands. But the snake has neither, and yet it is equally at home on the ground or among the branches. II. How THE SNAKE MOVES In order to find out how it is that the snake can move without any limbs, we must learn something about its structure, for its body is formed and adapted for this wonderful kind of movement. LES. xxxv REPTILES 91 1. The backbone. Show a picture of the skeleton of the snake. Call attention to the long string of separate bones which stretch through the whole length of the animal from head to tail. This is generally spoken of as the backbone, but in reality it consists of a large number of distinct and separate bones. The exact number differs in different animals. In the case of the snake these bones are joined together in a very wonderful way, and for a very wonderful pur- pose. Each bone has in front a kind of projecting knob like a round ball, while behind there is a cup-like hollow or socket, just large enough to hold one of these knobs. The whole string of bones is held together by the ball of one bone fitting into the socket of the one in front. We call these " ball-and-socket " joints. Show such a joint or a model of one if possible. Tell that we have a ball-and-socket joint in our own body at the shoulder. Put a boy through various movements with the arms, and show that a joint of this kind allows the greatest possible free- dom of movement. Lead the children to think again of the immense number of separate bones, all joined together by these ball-and- socket joints. What advantage does this give to the animal 1 It makes the body extremely flexible, and enables the animal to bend and twist easily in all directions. 2. The ribs. Return to the picture of the skeleton, and call attention to the short, curved, tapering bones which are arranged in pairs on either side of the backbone. These are the ribs. Man has ribs too, but only twelve pairs of ribs. Notice the immense number of ribs in this skeleton of the snake. One great snake has nearly 300 pairs of ribs. Explain that in man and in all the animals we have already studied, the ribs or most of them pass quite round the body, as 92 OBJECT LESSONS STAND, in hoops pass round a cask, and are joined to the breast-bone in front. -Here we see that the snake's ribs do not pass all round the body, and that the ends of all the ribs are free. Tell too that each rib is jointed to its own vertebra by a ball-and-socket joint. Lead the children to see the advantage derived from this arrangement. The ribs are thus enabled to move backwards, forwards, sideways in every direction. 3. The scales. Refer to the picture of the snake, and call attention again to the outer covering of hard, horny scales. Each scale partly overlaps the one behind it, so as to leave the hinder edge of all of them free. This we shall have to deal with presently. It is only with the scales on the under part of the snake's body that we have to do now. These are larger than the rest, and are joined by strong muscles with the lower extremities of the ribs. It is with these that the snake moves about as with so many legs. The ribs, as we have seen, can be moved forwards and drawn backwards, and each rib being connected with one of the under scales carries that along at the same time. When the snake, therefore, wishes to move, it first advances the ribs, and with them the under scales. These take a firm hold of the ground or tree on which they rest, and the body is drawn forwards with a gliding, creeping movement. Tell that the very name snake comes from a word which means to creep or glide. III. How THE SNAKE FEEDS Snakes, as we have seen, live on other animals. So do the cat and dog family, the mole, and others. How could we find out for ourselves, if we did not know ? By studying the teeth of the animal. Now, strange to say, the snake has no long canine LES. xxxv REPTILES 93 teeth for tearing, and no sharp jagged teeth for cutting through the flesh, as all these flesh-eaters have. It is not a flesh-eater. It does not eat the animals it preys upon as the flesh-eaters do. It swallows them whole. Examine the teeth in the picture of the skeleton. Notice that they are all small and sharp-pointed, and that they turn backward. Such teeth would be useless for tearing and chewing purposes. They are just suited for holding the victim between the jaws while it is gradually being swallowed. Show that the snake is specially constructed for this mode of feeding. 1. The head. In the animals we have studied only one part of the head, the lower jaw, is capable of move- ment ; and even this movement is somewhat limited. Tell that in the snake, not only the lower jaw, but the upper jaw as well is movable, and can be widely opened ; while the bones of both jaws, instead of being firmly jointed to the other bones of the head, are attached to them only by elastic muscular bands. Imagine a snake now in the act of swallowing its victim. It takes a firm hold with its teeth, and as these point backward there is no chance of their letting go while the act of swallowing takes place. All this time the jawbones have been widening and moving out of their sockets until space is made for the creature to swallow an animal much bigger round than itself. And so the victim passes down, and is swallowed whole. 2. The body. Now think of the ball-and-socket joints, by which the ribs are jointed to the vertebrae. Eefer to the freedom of movement which this arrangement gives to the ribs. Tell that as the body of the victim passes downwards after being swallowed, it simply pushes aside the ribs to make room. The overlapping outer scales readily slip aside too, as the body of the snake expands with its meal. 94 OBJECT LESSONS STAND, in Lesson XXXVI KINDS OF SNAKES SNAKES are found in most parts of the world, although they are by no means numerous in our own country. Snakes may be arranged in two great families the poisonous and the non-poisonous snakes. I. THE POISONOUS SNAKES As each class has its representative among our English snakes, we will examine these first 1. The adder or viper. This is the only poisonous snake found in England. It is therefore very necessary (especially for those who live in the more remote parts of the country) to be able to know the creature at a glance. It is mostly to be met with in the thickets and low brushwood of our forests and woodlands ; it likes to lie basking in the sun on the dry open heaths and sandy banks. Its hole or nest is sure to be found close to some such spots as these. Show a picture of the viper. Notice its size. It is very small, rarely measuring more than twenty inches in length. The head, pointed in front, is broadened behind the eyes so as to give it a triangular shape. But the great feature of the broad, flat head is the V- shaped mark between the eyes. Point this out on the picture, and show that it is formed by two black Stripes which meet there at an angle. Note also the long forked tongue. Tell tJiat ignorant people have imagined the tongue of the viper to be poisonous. It is quite harmless. In the living animal the tongue is restless ever on the move ; it is the snake's feeler. LES. xxxvi KINDS OF SNAKES 95 Call attention next to the body. Notice that the neck is somewhat smaller than the back of the head, and that the scales on the body are marked with dark zigzag patches. These black patches show up very distinctly against the general colour of the body, which is mostly olive, some- times brown, and sometimes brick-red. The fangs. In front of the upper jaw are two long, very curved, sharp-pointed, movable teeth. These we call the fangs. We cannot see them when the mouth is shut, for they are then drawn up and lodged in the gum. We sometimes call them poison-fangs ; but this is not quite correct, for there is no poison in the fangs them- selves. The poison comes from two bags lodged in the back part of the mouth. The fangs themselves are really hollow tubes, and when the snake is about to dart at its victim, not only do the fangs show themselves, but the hollow tubes within them carry a quantity of poison, which the poison-bags pour into them for the occasion. The adder or viper preys upon rats, mice, and birds. To them its bite is fatal. It is dangerous, though not often fatal, to people, except to delicate, unhealthy persons. It is extremely voracious and will often devour more than it is able to digest. Tell of its mode of attacking its victim its stealthy, gliding, noiseless movement, until within striking distance, then a lightning-like dart forward. One bite is quite sufficient, for the sharp tooth not only makes a wound, but at the same time leaves a quantity of poison in the wound, which soon kills the victim, or renders it insensible, so that the snake can gorge it at its leisure. 2. Other poisonous snakes. Tell that the poisonous snakes of many foreign countries are much more to be feared than our English viper, because they are larger and their bite is much more deadly. Describe the dreaded rattlesnake of America. 96 OBJECT LESSONS STAND, in It is usually about 5 feet long, and receives its name from a sort of rattle which it has at the end of its tail. Tdl the use it makes of this rattle when angry. Mention the hooded snake of India and the deadly cobra. Tell their method of trying to strike terror into their victim, and so rendering it powerless to escape before they strike. II. NON-POISONOUS SNAKES 1. The common snake. Show a picture of the common English snake. This is larger than the viper and often attains the length of three feet. It is quite harmless. In fact, children in the country often catch these snakes and tame them as playfellows. The general colour of the upper part of the body is a sort of greenish -brown or grey tinged with olive. The belly is of a leaden colour. There are always two rows of larger spots down each side. Point out these spots on the picture. In the living animal, they show up very distinctly on the lighter ground-colour. Across the back of the neck, behind the head, is a broad yellow stripe edged with black which looks like a ling or collar. It is this which gives it the name of the ringed snake. The head too is different from that of the viper. Instead of being flat and triangular and broader than the neck, it is long and slender. It has no black V-shaped mark, no sharp poison- fangs, and (if we could see within the mouth) we should find no poison-bags there. Neither has it the cruel, deadly look of the viper. Its food consists of frogs, eggs, mice, young birds. It is extremely fond of the water, and is a most graceful swimmer. It usually makes "its home in damp woods, meadows, and hedges, and by the side of ponds where its favourite food, the frog, is found. LES. xxxvn THE FROG 97 It may frequently be seen basking on a sunny bank close to its hole. There is another kind of snake sometimes met with in this country. It is called the smooth snake. In size and colour it is rather like the viper, but in every other respect it resembles the common ringed snake, and it is perfectly harmless. 2. Other non-poisonous snakes. The non-poisonous snakes oMoreign countries are usually of enormous size and strength. Show a picture of the great boa -constrictor and the python. Their usual Lngth is from 20 to 30 feet; but they often reach the prodigious size of 40, 50, and even 60 feet. They coil themselves round the trunk of a tree and lie in wait for some animal (often larger than themselves). One sudden spring and the animal is entirely within their power. They twist and coil themselves round the body of their victim, their enormous strength enabling them to crush it, bones and all, into a mangled mass. They then swallow it whole, after which they creep away, with their skin distended almost to bursting, to some qujet spot, to sleep while the work of digestion goes on. This often lasts for a month, and when the pangs of hunger awaken them, they go and look for another victim. Lesson XXXVII THE FEOG I. GENERAL DESCRIPTION Snow a good picture of the frog, and provide also a living specimen if possible. This in most cases would not be a difficult matter if the services of a few boys were called into requisition beforehand. Lead the children to work out the description of the animal. VOL. IT H 98 OBJECT LESSONS STAND, m 1. The head. The head is very large and broad and somewhat triangular in shape. It is set square on the shoulders without anything approaching a neck. Call attention to the extremely wide mouth and the enormous goggle eyes, with their yellow edges, looking like a pair of gold-rimmed spectacles. The eyes are, in fact, the most prominent feature in the head. They occupy nearly the whole of the head, leaving very little room for brain. Hence the frog is a very stupid creature. If we examine the inside of the mouth, we shall find that the upper jaw contains a row of sharp, pointed teeth, but that there are no teeth in the lower jaw. Perhaps the most wonderful thing about the frog is its tongue. Shoto a picture of this if possible. Explain that the frog's tongue, instead of springing from the back of the mouth as the tongues of most animals do, has its root in front, and actually points backward towards the throat. It can, when it wishes, however, throw the tongue forward, and then the tip reaches a long way beyond the mouth. It makes great use of its tongue, as we shall presently see. 2. The body. Notice the broad, squat, ungainly shape of the body. In fact it can scarcely be said to have any shape at all. Tell too that the animal has no ribs. There are some short projecting bones on each side of the backbone, but no actual ribs. Show a skeleton of a frog. One may easily be obtained by putting a dead frog into an ant's nest and leaving it for a week or ten days. 3. The skin is usually of a greenish -brown colour, with the under parts yellow. It is very porous, and absorbs water like a sponge. If a frog be put into a dry place, its skin shrinks and becomes stiff, and the animal itself grows thin and wretched-looking, and would soon die ; but if it is put back into a damp place it rapidly recovers. LES. xxxvn THE FROG 99 Frogs dislike heat, and in hot weather they always hide away under the broad leaves of cabbages and other large plants, or in some cool spot. For the same reason they always make their homes near the banks of ponds and ditches. Notice that the skin is always covered with a slimy fluid. 4. Legs and feet. Call attention to the animal as it sits up in its favourite resting position, on its haunches. Notice the disproportionate size of the hind as compared with the short fore legs. Point out that the hind feet have five toes of extraordinary length, the front ones four. Lead the children to tell of the frog's mode of travelling by hops or leaps. Show with the living specimen. Set it down on floor. The frog uses its strong hind legs, with their long toes, in leaping. Notice next the webbed feet. What does this tell us ? That the animal is a swim- mer. It is as much at home in the water as in the green fields. Describe the graceful movement of the frog in the water ; or put the living one into water, and let it show for itself. The frog is a very hardy creature ; neither cold nor hunger seems to hurt it. II. THE FROG AND ITS FOOD The frog preys upon living insects, cockroaches, flies, slugs, grubs, worms, and snails. It is therefore one of the gardener's best friends, for these vermin are very destructive in a garden. It never attacks its prey when they are perfectly still. It will only catch insects when they are on the move. It always swallows its prey whole, so that the row of teeth it has are not meant for chewing or tearing purposes. 100 OBJECT LESSONS STAND, in It is when it is trying to swallow larger prey than mere flies and grubs such as an earthworm that it finds its row of teeth useful. Describe the frog in the act of swallowing a worm pushing with its fore paws the worm into its mouth, while the teeth hold it securely in spite of its struggles to get free. Its great fleshy tongue, however, is its principal feeding-organ. It is the frog's fly-trap. Let the children describe this organ again. Tell that it is always covered with a thick, slimy matter which acts like bird-lime if once a fly touches it. Picture the frog lying motionless in wait for its prey. Pre- sently a fly comes within striking distance, the tongue is darted forward with the rapidity of lightning, and carried back to the mouth again. But the fly has gone with it, and is swallowed. Lesson XXXVIII THE FROG I. RECAPITULATORY LEAD the class to tell what they were taught last lesson about this animal its structure, habits, and food. We have more to learn now about this wonderful little animal. II. How THE FROG BREATHES Tell briefly of the mechanism of respiration in ourselves and most animals around us. The ribs form an air-tight box which holds the lungs. The ribs are constantly rising and falling so as to enlarge and diminish the capacity of that box and of the lungs themselves. As they expand, air rushes in at the mouth and nostrils to fill them, and when they fall, the air is driven out again. LES. xxxvni THE FROG 101 This constitutes the act of breathing, and it is always going on, without any effort on our part. Now the frog, as we have seen, has no ribs, and its lungs, therefore, cannot be expanded in the same way as ours are, so as to take in air. It must have air, however, and therefore it is com- pelled to swallow it in gulps, as we swallow our food and drink. It closes the mouth and sucks up a quantity of air through the nostrils, swallowing each draught with a special effort. It cannot take in much air in this way, but it is assisted in breathing by its moist, porous skin, which also absorbs a small quantity of air. During the winter, when flies and grubs are not to be found, the frog betakes himself to the bottom of the pond, scoops out a hole for himself in the mud, and there sleeps till the frost and snow have disappeared, and warm spring has come once more. All this time his skin has to do the entire work of breathing or taking in air from the water, for the frog cannot breathe under water with its lungs. Even with lungs and skin too, however, the frog takes in but little air. Tell that it is the air we take in that gives heat to the blood and the body. Picture a man or a horse doing hard bodily work. They breathe rapidly, i.e. they take in more air than usual, and soon become very hot. The frog takes in so small a quantity of air, that it is not enough to warm its blood. Its blood is always cold. We say it is a cold-blooded animal. It has no need to keep heat in its body, as warm- blooded animals have, hence it is not provided with a warm coat, but has a naked skin, which always feels cold and clammy to the touch. 102 OBJECT LESSONS STAND, in III. COMPARISON WITH A TOAD The toad is an animal belonging to the same class as the frog. The toad, however, differs from the frog in several particulars. In the first place it is more clumsily built, and moves about with a slow, crawling gait. Its legs are so short that it cannot leap as the frog does. It is a land animal and cannot swim. It hides during the day in damp spots, and comes out after sunset to prey upon insects, slugs, and worms. It has no teeth. Ugly and awkward as it is, it is quite harmless. Indeed it is most useful in the garden in destroying slugs, caterpillars, earwigs, and other vermin. Lesson XXXIX THE FROG ITS LIFE-HISTORY THE frog which we saw in our last lesson would (if it could be made to tell its own history) have a wonderful story to relate. As the frog itself cannot speak, I will tell its story myself. I. THE EGG It was Once an egg, floating on the surface of the water in some pond or ditch. Frogs, as we know, are very fond of the water, and they spend a great deal of their daily life in the water. They take their long winter-sleep in the mud at the bottom of the pond. But they also lay their eggs in the water. LES. xxxix THE FROG ITS LIFE-HISTORY 103 Tell that almost all reptiles, with the exception of some of the snakes, produce their young from eggs. (The viper brings forth its young alive.) But what can induce the frog to lay its eggs in the water? What do birds do when they have laid their eggs 1 They sit upon them and hatch them with the heat of their own bodies. Why does not the mother-frog act in the same way 1 The frog has no warmth in its cold-blooded body ; it cannot hatch its own eggs. It simply lays them at the bottom of the pond, and leaves them there. They soon rise to the surface of the water, and during the early part of April may be seen floating about, or clinging to the weeds, like a mass of dirty-looking jelly, filled with little black spots. These black spots are the eggs themselves, and the warmth of the sun hatches them as they float about. II. THE TADPOLE The little creature that comes from the hatched egg is not a frog. It is altogether unlike a frog. It looks like a very large head with a very long, flat, waving tail coming straight out of it. We call it a tadpole. Tell the probable meaning of the name tad = tailed, poll = head. If this lesson could be suitably timed, it would be well to call in the services of some of the boys a week or two beforehand, and so provide some living specimens of the tadpole in various stages of their growth. They may be shown in a glass bowl or a basin. Notice that they are quite at home and happy in the water. They are, in fact, formed to live in the water. If we took them out of the water they would die. The tadpole is very like a fish. Show in the living specimens, or on the pictures, the little pink gills at each side of the head. 104 OBJECT LESSONS STAND, in Tell their use for breathing in the water, and compare them with the gills of the fish. Show the gills of some common fish. Fishes and tadpoles have no lungs as we have. They have gills instead. They cannot breathe out of the water ; we cannot breathe in it. Turn to the picture again, and show that the tadpole has its mouth placed, not in front of the head, but rather under it. Tell that this mouth is specially fitted to nibble off the soft shoots of the water-plants upon which it feeds for it lives entirely on vegetable food. Lead the children now to compare the tadpole with the parent frog in its general appearance, its mode of breathing, its food. Why did the mother-frog lay her eggs in the water ? III. THE CHANGES The tadpole continues its water-life for four, six, or sometimes eight weeks, according to the condition of the weather. It remains longer in this state in a cold, damp spring, than in a warm, bright one. All this while, however, it is undergoing wonderful changes. It feeds very greedily on its vegetable food, and grows quickly. After a time, two little humps begin to make their appearance, one on each side of the tail, just where it joins the hinder part of the body. These little humps grow rapidly, and after a time take the form of hind legs. But notice what has been taking place besides. The long tail is gradually wasting away, and by the time the hind legs are formed, it will have become loose, and at last it tumbles off. Show a picture of the tadpole in this state, or letter still, if possible, the living specimens. LRS. xxxix THE FROG ITS LIFE-HISTORY 105 But other changes have also been going on indeed are going on. As the body grows, the gills commence to shrivel up, and become smaller and smaller, and lungs are developed within. The eyes also begin to push themselves outwards, and become prominent, as seen in the frog. But how is this ? The frog has four limbs, and this tadpole we have examined has only two. Tell that before the hind legs are fully developed the front ones begin to appear as little lumps under the skin. They soon force their way out, and take the form of legs and feet. Show the tadpole-frog with the four limbs fully developed. It is difficult to know what to call it now. It is scarcely a tadpole, for its long, waving tail has entirely disappeared ; it has four legs and feet fully developed ; its head and body have grown large and broad ; and its mouth, which was some distance under its chin (so to speak), is now quite in front of the head, and has become large and broad. Presently the last vestige of the gills disappears, and the creature begins to find itself unable to breathe in the water. Making its way by instinct to the surface of the water, it finds it can breathe air through its lungs. It at once leaves the water, and commences a new kind of life in the green fields a frog at last. It soon begins to feel the pangs of hunger, but it has now no appetite for the green vegetable food around. It has a craving for animal food. It has become a flesh-eater, and a very greedy flesh- eater too. It still continues to grow, as a frog, and as it grows it sheds its skin from time to time. The snake also sheds its skin, but the frog actually tears off its skin with its paws and swallows it every bit. Fancy a boy dragging off his coat and swallowing it, svhen it got too small for him. 106 OBJECT LESSONS STAND, in Lesson XL A FISH SHOW a mackerel or a herring as a type of the commonest sort of fish. We are now going to study a new class of animals animals that live all their lives entirely in the water, and could not live out of it. We shall learn how fishes are fitted to live in the water ; how they breathe ; Juno they move about without legs ; how they feed, and so on. I. How FISHES BREATHE A man, a dog, or rabbit would die if held under water. The fish dies directly it is taken out of the water. Yet both die from the same cause both are suffocated. The one cannot breathe in the water, the other cannot breathe out of it. Hence the first thing to puzzle us with regard to a fish is, how it can live and breathe in the water. 1 . The gills. Now look at these long slits or openings on either side, just behind the jaws. Watch while I lift this one up, and tell me what you see underneath it. A bunch of red, fringe-like leaves. These are the gills. Tell tJiat the fish has no lungs such as we have, that, in fact, the gills are the lungs of the fish. Fishes cannot live without breathing air any more than we ourselves can. We breathe by means of lungs, the fish by means of gills. But how can a fish breathe air, while it is living and moving about in the water 1 The water contains air. liefer to the earlier lessons on water, and remind the class that water itself is porous and absorbent ; that it absorbs air ; that, in fact, water always contains air. LES. XL A FISH 107 The fish lives by robbing the water of some of this air, which it breathes in through its gills. We might drive all the air out of a quantity of water by boiling. If we then put a living fish into it, the fish would die at once. It would die of suffocation, or want of air ; for although the fish lives in the water, it breathes air and not water through its gills. Sho\v, if possible, a living fish of some sort say a gold- fish in a glass globe. Call attention to the fact that the fish is constantly opening and shutting its mouth, as if it were drinking. Tell that it is not really drinking that it is not taking in water and swallowing it. It takes the water into its mouth, but only to pass it backwards over the gills, and so out again through the slits at the sides. Now why is this always going on ? Let us have another look at the gills of the herring. In the dead fish, the gills look dry and shrivelled, they became so as soon as the fish was taken out of the water. But in the living animal, they were larger and fuller. Why should they be red ? This we could easily learn by examining them under a microscope. We should then find that they are really crowded with tiny blood-vessels, and it is the blood in these vessels which gives the gills their red colour. Now let us see what happens every time the fish takes in water through its mouth and pours it over the gills. The blood in the little vessels all over the gills sucks up as much of the air as it can get from the water. This is the creature's way of breathing. 2. Fishes are cold-blooded. Lead the class to see that the fish cannot get as much air from the water as we and all lung-breathing animals can from the air. We live and move about in an ocean of air itself. Refer to the lesson on the frog, in which we introduced the cold-blooded animals, and let tJie children tell, this time, that our 108 OBJECT LESSONS STAND, m bodies are warmer or colder according to the amount of air we breathe in. Elusirate by a boy running, a man doing hard work, or a horse drawing a heavy load. Fishes take in so little air by their gill-breathing that it is not sufficient to warm their blood or their bodies. They are always cold. We call them cold-blooded animals. Having no heat in their bodies to keep in, they have no need of a thick warm coat. Hence they are never clothed in wool, fur, or feathers, or even with a thick hide, and their bodies always have a cold clammy feel. II. How FISHES ARE CLOTHED This leads us to the next part of our lesson the covering of fishes. There is another reason why wool, fur, or feathers would not make a good covering for the fish. Try and find out what I mean. Here is a smooth piece of wood. See how easily I can push it through the water. Now I will cover it with wool or fur, and try again. What do I find 1 It is not SO easy to force the stick through the water now, because the thick, woolly covering resists the water. Explain that the bottom and sides of ships even must be kept clean and smooth if they are to move quickly through the water. Now tell me why wool, fur, or feathers would not make a good coat for the fish. Because they would interfere with the movements of the fish in the water. Show the herring again, and call attention to its shiny, silvery-looking coat. Take up some of the loose scales on the finger and let the children examine them. This coat is made up of a multitude of these little round LES. XLI A FISH 109 scales, overlapping each other and embedded beneath the skin in front. The body of the fish is really encased in a coat of mail. Run the finger along the fish from head to tail. Its coat is very smooth. Rub it in the opposite direction and the scales ruffle up. The proper way of removing the scales in order to prepare the fish for cooking is by scraping it with a knife from the tail upwards. As the fish moves onwards through the water, then, its scaly coat is pressed closer and closer to its body, so that it offers no obstruction to its movements. Let one of the children take the fish in his hands and describe its slimy, slippery feel. Tell that fishes are able to send out and pour over their bodies a sort of slimy oil, which helps them to glide easily through the water. Lesson XLI A FISH I. HOW THE FlSH MOVES INTRODUCE the lesson by leading the children to describe the scaly coat of the fish, and its covering of oily slime. Let them show how such a covering affects the freedom of movement of the fish in the water. The movements of the fish are assisted by its structure in other ways, 1. The shape of the body. Take a small wedge of wood and let one of the children force it through the water, first with the base foremost, then the thin edge. Let them tell which end moves with greatest ease through the water, and why. The sharp edge cleaves, or cuts the water. Now yhow the herring. 110 OBJECT LESSONS STAND, in Its body, big in the middle, tapers to a sharp point both ways. It is like a pair of wedges joined together at their bases, except that all sharp corners are nicely rounded off. The herring's body is just of the shape to enable it to cleave its way through the water with the greatest possible ease. 2. The structure of the backbone. Show the lack- bone of a fish a mackerel will do very well for the purpose. Separate some of the vertebrce to show how they are joined. Show that each vertebra has a hollow socket on both sides, and that the bones are joined by the rim of one socket fitting closely to that of the next, thus forming a sort of hollow ball between the two. This ball is filled with an oily fluid, which helps the edges to move freely upon each other. The great thing needed in the body of the fish is flexibility. Show the fish in the glass globe. Notice the graceful, easy way in which it twists and turns in the water. This is admir- ably secured by such an arrangement of the vertebrce as we have described. Compare it with the backbone of the snake and that of some common animal, such as the rabbit. 3. The mechanism of moving. We have thus far noticed the aids with which the fish is provided to render its movements easy. We must now find out how it is that the fish can travel through the water at all. The fins. Show the herring once more. Point out the feathery fins and their position. Notice first a pair, one on each breast, just behind the gills. These are the breast -fins. Then there is another pair, also on the under part of the body, near the middle of the stomach. These are the belly-fins. Tell that these four correspond to the four limbs of land animals. Besides these, there is generally a large fin on the back, and one more under the body near the tail. LES. XLI A FISH 111 The largest and most important one of all is the broad upright fin at the end of the body, that which we generally call the tail. Its proper name is the caudal or tail-fin. Explain the application of these several terms. Let us see why we call the last the most important of all. Tell of a boatman propelling his boat by means of a single oar at the stern of the boat. The tail-fin is to the fish what the oar is to the boat. It does all the work of propelling the fish through the water. The other fins are useful to balance and guide the fish in its movements. II. HOW THE FlSH FEEDS Fishes, as a rule, feed on one another, and hunt their prey through the water as the lion, tiger, and other fierce flesh-eaters hunt theirs on the land. They are almost all l very rapacious, and, from the largest to the smallest, prey upon and devour each other. This explains why easy and rapid movement is so necessary to these creatures of the water. At one time they are the hunters, at another, the hunted prey. Let us examine our fish and try to find out how it goes about its water-hunting. Where shall we look to find out what we want to know ? In its mouth. Open its mouth and show that it is well provided with teeth. Show that the teeth are numerous, but very small ; they are simply little sharp spikes, and they all point back- wards, towards the throat. Fishes have no teeth either for tearing or chewing. Now let us see what all this teaches us. The teeth must seize the prey, they must also be strong enougli to hold the struggling, slippery victim fast, because as the fish has no tearing or chewing teeth it 1 N.B. The carp family are without teeth, and do not prey on other fish. 112 OBJECT LESSONS STAND, in must swallow its prey whole, without waiting to chew it. III. FISHES AND THEIR YOUNG Fishes are produced from eggs. Open the herring (first seeing that it has a " hard roe "). Take out the roe, and tell that each little grain of the roe is a tiny egg, which might have produced a young fish. What an immense number of eggs from one single fish ! The eggs, after they are deposited in water by the parent-fish, are called " spawn," and the spawn forms the favourite food of many water animals. Even the tiny young fishes that come from the spawn of one kind feed on the eggs laid by others. Then, too, these same young fry (as the little baby-fishes are called) form the chief food of all others that are large enough to prey upon them. This explains why one single fish is made to lay such a multitude of eggs. Tell that the eggs of the cod-fish float on the surface of the sea till the heat of the sun hatches them ; while those of the herring sink to the bottom of the shallow waters in which they are laid, and there stick to the rocks and sea-weed. Some fishes, that properly belong to the sea, always swim up the rivers to lay their eggs in some shallow place in the fresh water. The smelt, salmon, and trout are members of this class. Lesson XLII AN INSECT Snow a good picture of a few of the common sorts of insects, such as the bee, common house-fly, butterfly, moth, beetle, grasshopper, ant, n\><] of molecules of matter. Ijd a boy try to break it with tJte Jiammer, or twist it out of sJtape. LES. i MATTER 1'27 He cannot. Why is this ] Let us see what we mean by breaking. It really means separating one from another the particles the molecules of which the thing is made. Now evidently if we cannot separate these individual particles from one another there is some force which holds them together. We call this power, which holds the molecules of matter together, the force of cohesion. Cohesion itself means holding together. Illustrate further with pieces of lead, wood, glass, and chalk, to show that the force is not equally strong in all bodies. The lead and wood bend and twist, but will not readily break. We say they are tough. The glass and the chalk break easily, and we say they are brittle. Still there is cohesion in the most brittle bodies. Picture the world suddenly left without this force of cohesion. Everything round us, the world itself, we ourselves even, must fall to the finest dust or powder. Let us see how this force acts. Here is a brick. We will first of all break it into very small particles. Now, can I gather these particles all together and press them into the form of a brick again ? I cannot ; no amount of pressing would do it. Why is this 1 Tell that 'if two sheets of plate-glass, very smooth and level, be laid one on the other and pressed, the force of cohesion at once acts, and it is impossible to separate them. Show the two edges of a broken plate. It is useless to try to join these by pressing them together in the same way. Now why can we join the sheets of glass so as to make them cohere, and not the particles of the brick, nor the broken edges of the plate 1 The force of cohesion can act only when the particles are in actual contact with each other. The two sheets of glass were so perfectly smooth and 128 OBJECT LESSONS STAND, iv level that all their particles were in actual contact as they lay one on the other. Hence cohesion acted and joined them. Show how the same may be done by cutting a leaden bullet or a piece of india-rubber in two, and pressing the clean-cut surfaces together. We cannot make the force act on the particles of the brick or on the broken edges of the plate, because we cannot bring all the particles into actual contact ; and without actual contact there is no cohesion. III. SOLIDS, LIQUIDS, GASES What we have just learned about the force of cohesion will help us to understand better than we have done the nature of the three states of matter solids, liquids, and gases. 1. A solid is a body whose molecules are held firmly together. It is a solid simply because the force of co- hesion is very strong in it. If we break a soft solid, like a piece of chalk, it does not fall to powder. It breaks into pieces, and these pieces still hold together. 2. A liquid. Produce a basin of water, and set one of the children to take the water out, a spoonful at a time. Let him tell that he does it without any difficulty. Why is this 1 The particles of the liquid are not held together firmly by the force of cohesion as those of solids are, and he finds it quite easy to separate them one from another with the spoon. The force of cohesion is not so strong in liquids as in solids. 3. A gas. Make the children tell tJie chief cJiaracteristic of a gas. Its particles are always trying to get as far away from each other as possible. They repel each other. Illustrate by a slight escape of gas in a room. The particles soon seem to fill tlie whole room. In a gas, tlien, the force of cohesion does not ad at all. LUS. ii CAPILLARY ATTRACTION 129 Lesson II CAPILLARY ATTRACTION I. ADHESION WE have seen that it is a very difficult matter to join the particles of a solid, and if we were to examine their sur- faces through a microscope we should see the reason. Smooth as they might appear to the naked eye, the magnifying glass would prove them to be so rough and uneven, that it would be impossible to make them touch at all points. Hence there can be no cohesion, no joining. It is an easy matter to make a liquid and a solid join, because the liquid flows and fills up all the hollows in the solid. Illustrate by reference to the use of gum, paste, glue, melted sealing-wax, mortar, etc. Explain that the gum, glue, or mortar fills up all the hollows and pores of the solids which are to be joined, and thus by touch- ing every part on both sides is able to hold the two together. The force which holds them together in this way is called adhesion, and the various cements are said to be adhesive substances. II. POROUS ABSORBENT Let the children tell the meaning of the word porous, and make them enumerate as many examples of " porous bodies " as possible. Such bodies are absorbent, that is, they suck up liquids through their pores. liefer to the illustrations in the early lessons with sponge, salt, loaf-sugar, blotting-paper, string, lamp-wick. Repeat one or two experiments, e.g. the coloured water and chalk, and the paraffin and piece of cane. VOL. II K 130 OBJECT LESSONS STAND, iv We have been content to say hitherto that these substances are absorbent, because they are porous, and liquids rise up through their pores. We can go farther than that now. I have here a piece of glass tubing with the bore as fine as a hair. In this tumbler is some coloured water. Now watch and tell what happens when I stand the tube in the water. The coloured liquid rises a long way up the tube. We say it does this by capillary attraction. The word " capillary " comes from a word which means " like a hair." Liquids rise in all porous bodies in this way, for their pores are really very fine tubes. But why should liquids rise in such tubes 1 This is due not to cohesion, but to the force of adhesion between the liquid and solid through which they are rising. There is adhesive force between the oil and the wick, and between the paraffin and the cane, and it is this adhesive force which causes the liquids to rise gradually through the pores or hair-like tubes of the porous solids. Lesson III PROPERTIES OF SOLIDS IN our early lessons we dealt with some of the properties of solids. We are now in a position not only to say that certain bodies are hard or soft, brittle, or. tough and flexible elastic, malleable, ductile, tenacious, heavy, but also to examine into the reason why they possess these properties. Write the names of these properties on the black-board, and deal with them one by one. I. HARD AND SOFT Lead the children to tell what is meant by hard and soft ; and that the terms are really comparative. LES. in PROPERTIES OF SOLIDS 131 Chalk is hard compared with an apple, but soft when compared with stone ; oak wood is hard compared with cork, but soft compared with iron. We frequently compare one solid with another by rubbing the two together ; the harder will cut or scratch the softer body. Thus iron is harder than lead, for an iron nail will scratch lead, and a steel knife will cut it ; but the same knife will neither scratch nor cut diamond, because diamond is harder than steel, Now why should one body be able to scratch another in this way ? You will say because it is harder. Then why is it harder ? Let us think again of the force of cohesion. When the force of cohesion in a solid is great, the molecules are held very closely together, and the solid is hard. When there is little cohesion, the molecules are more loosely held together and the body is soft. It is because the particles of the soft body are held loosely that the hard substance is able to force them aside as it does when it scratches them. II. BRITTLE, TOUGH, FLEXIBLE, ELASTIC Strike a piece of cork with a hammer. Does it break 1 No. Do the same with a piece of chalk, lump-sugar, and brick. These break with the blow. Try to bend a piece of whalebone, cane, lead, or cork, and some copper and iron wire between the fingers. They bend easily without breaking. Do the same with a stick of slate-pencil, glass, or chalk. These snap, but will not bend. Make the children tell that the chalk, sugar, brick, pencil, and glass are brittle ; the pieces of wire, cork, whalebone, lead, and cane are tough and flexible. 132 OBJECT LESSONS STAND, iv Now we shall have to go back to the force of cohesion to find the reason why certain bodies have these properties. When the cork, whalebone, lead, cane, and wire are bent and twisted, it is clear that their molecules are forced out of their proper position ; and it is because the molecules of chalk, glass, etc., will not be forced out of their position that they break rather than bend. The whalebone, cork, and cane not only bend but spring back when let go to their former shape, each little particle taking up its old position. They are elastic. Deduce this from the earlier lessons. HI. MALLEABLE, DUCTILE, TENACIOUS Show some gold-leaf, lead and tin foil, and some sJieet-iron. How were these made t They were either hammered or rolled out into these thin sheets. Could we do the same with a piece of coal, brick, or chalk ? No. Their particles would separate with the hammering. They are brittle. Why can we do it with the other substances ? They are malleable. Let the doss tell the meaning and derivation of the word. Malleus = a hammer. Now show some specimens of wire, some thick and some thin. How were these made ? Lead the class to tell the meaning of the word ductile. Take a piece of lead and beat it on a flat iron. The hammering has made the lead larger, broader, and thinner. This really means that its molecules have been forced into different positions. Because they do this without losing their cohesion, the metal holds together, and we say it is malleable. Illustrate the drawing out of wire by heating a thin glass rod. Show that the glass becomes softened, and in that state may be drawn out into wire. LES. iv WEIGHT 133 The molecules again are made to take up a different position, and they do so without losing their cohesion. In fact, no substance can be ductile unless there is very strong cohesive force between its molecules. Without this force the substance will snap asunder. This is what we mean when we say some metals are tenacious, others are not. IV. HEAVY Show pieces of cork, wood, stone, and lead of about equal size ; and, let the children note their respective weights. We know that one substance differs from another in weight, and we say that bodies are light or heavy. But why are they light or heavy ? Tell that this is a question we shall deal with in another lesson. At present it will be sufficient to remember that in a heavy body the force of cohesion is stronger than in a light one the molecules are held more closely together there is more matter in it. Lesson IV WEIGHT TAKE the pieces of cork, wood, stone, and lead that were shown in the last lesson, and make the children tell what they have already learned as to their respective weights. Why should one be heavier than the other ? The force of cohesion is not the same in all bodies. In some it is very strong, and holds the molecules very closely together, so that more matter is massed together into a given bulk than if there were less cohesion. It is so with the lead and stone as compared with the wood and cork. 134 OBJECT LESSONS STAND, iv L WHAT WE MEAN BY WEIGHT You can tell me that bodies are light or heavy. Let us try and find out what we mean when we say this. Bring a boy to the front and place in his open hand, one by one, the cork, wood, stone, and lead. Let him hold them at arm's-length, and lead him to tell that each of them seems to press his hand downward, although the lead presses more than the others. What would happen if he let them go ? They would fall they neither mount up into the sky, nor move off sideways, but fall always to the ground. Show a bag of feathers equal in bulk to the other bodies. Feathers are very light. Would the bag of feathers fall to the ground too if let go ? Let us see. Yes. Show that this applies also to liquids. Let a boy hold an empty vessel at arm's-length while it is slowly filled with water. Make him explain that there is the same downward pressure, and that the pressure increases with the increase of water in the vessel. What would happen if the bottom of the vessel were to fall out ? The water would fall to the ground. Lead the class to tell that in each case the pressure on the hand and the tendency to fall were caused by the weight of the body. Illustrate with any other substance convenient to hand, and lead the children to see that all press downward, and all would fall to the ground if let go. Even a single feather, light as it is, must fall. What does this tell us ? That all have weight. II. UP AND DOWN We have seen that all bodies let fall from the hand come to the ground. But suppose I went to the top of this school and dropped a ball or stone in the air, what would happen then ? It would fall to the ground. LES. i-v WEIGHT 135 Suppose I did the same from a balloon sailing very high in the air ? The stone would fall to the ground. So we may say all bodies unsupported fall, and always fall in one direction. What is that direction 1 Down- wards. What is the direction opposite to this? Up- wards. I can throw a ball upwards to a certain height, but after going some distance it will be sure to fall downwards to the ground again. Up, then, means towards the sky ; down towards the ground. Now I want you to think a few minutes about this earth on which we live. You all know that it is a great ball, and that you and I and everybody live and move about on the outside of the ball. Show a globe. Let the children point out England and New Zealand on opposite sides. We are living on this spot. Point to it. Draw a circle on the black-board to represent the globe, marking the spot indicated. Now "suppose I wanted to represent some tall building (say the monument) towering up into the sky, how should I draw it ? Would this be right ? Draw a line from the spot perpendicular as to the board itself. Show that such a line would not be perpendicular to the surface of the earth, but slanting. Draw the correct line, and show that if produced it passes through the centre of the circle. Do the same from other points on the circle, and show that in each case the line must pass through the centre of the circle. But the top of the monument points up, and the bottom down. Now let us think of the people of New Zealand and their buildings. Their feet stand on the earth, and their heads point to the sky ; their buildings rest on the earth and tower towards the sky just as ours do. 136 OBJECT LESSONS STAND, iv What sort of line would represent them ? Have it drawn. Produce it. What do we find ? It passes, like the lines on the other side of the earth, through the centre. Now think of the man in the balloon again. Suppose the balloon went up in New Zealand. Show with the globe in what direction the balloon would move. Now let him drop his stone out of the balloon. What would be the direction of the falling stone ? Let us represent this direction with a line on the circle, and produce the line. What do you see ? That line too passes through the centre. Who can tell me now what we mean by up and down ? Up means towards the sky ; down means towards the centre of the earth. III. GRAVITY So, then, all bodies when unsupported fall downwards, and down means towards the centre of the earth. Why should they fall, and fall always in one direction 1 They fall because the earth attracts or draws them towards itself. There is a force which acts from the centre of the earth and draws every body towards that spot. We call this force gravity. It was the force of gravity which caused the feeling of downward pressure when the different bodies were held in the hand. The earth was trying to draw them downward towards itself. But why should it draw certain bodies more than others ? Because the earth attracts bodies in proportion to the amount of matter which they contain, and some bodies, as we have seen, contain more matter than others. It is the force of gravity which gives substances weight* The very word gravity means weight. LES. v LIQUIDS 137 Lesson V LIQUIDS I. COHESION IN LIQUIDS LEAD the children to talk of tJie difference between solids and liquids both being made up of molecules, but the force of cohesion being great in solids and weak in liquids. In a solid, so great is the force of cohesion that the molecules cannot shift about. The molecules which to-day form the extreme end of this iron rod will not to-morrow have moved into the middle, but will remain where they are. In liquids there is very little cohesion. The molecules of a liquid are free to move about, roll one over the other, and change their places. Show a tumbler of water ; move a knife or a stick through the water. No great force is required, because the molecules are pushed aside easily. Do the same with a tumbler of pease, shot, or small round Imagine the water to be made up of extremely fine round molecules many million times smaller than a pea, all the molecules being free to move, because there is little cohesion between them. II. LIQUIDS DIFFER IN COHESIVE POWER Show two tumblers holding equal quantities of water and treacle respectively. Slant them from side to side to show the difference of move- ment in the two liquids. Stir with a knife. Turn the tumblers upside down, and note how slowly the treacle runs in comparison with the water. 138 OBJECT LESSONS STAND, iv Why is this ? Tell that there is more cohesion between the molecules of treacle than those of water, and that therefore they separate more slowly. Let the children mention other liquids which resemble treacle in this respect, e.g. tar, glycerine, castor-oil, liquid gum. We call them viscous liquids. Alcohol, ether, and benzoline, on the other hand, are types of liquids which have less cohesion than water. Their molecules move about very freely indeed. We call these mobile liquids. Explain the meaning of these terms. III. LIQUIDS HAVE NO SHAPE Point out again that in a solid the force of cohesion is strong, and holds each molecule in one position. Thus the whole solid body has a definite shape of its own. In a liquid, on the contrary, there is little cohesion and the molecules are free to move about in any direction. Hence a liquid cannot have any fixed or definite shape. Pour the tumblerful of water into a basin, a jug, and a bottle, and call attention to its repeated change of shape. Why is this ? Tell that the force of gravity draws the molecules downward to the bottom of the vessel ; they cannot stand in a heap, because those above press on those below, and push them into every corner of the vessel, and the molecules force one another downward and outwards in this way until they meet with the bottom and sides of the vessel. Thus a liquid can have no shape of its own, but at once takes the shape of the vessel which holds it. IV. SURFACE OF LIQUIDS Call attention to the fact that although just now we poured the water into variously shaped vessels, its surface was in every case level. LES. v LIQUIDS 139 Fill a tumbler with flour or sawdust. Pile it up in a heap on one side of the glass. Could I do the same with the water ? No, the water would run down and become level again. Why should this be ? Tell that the solid particles of the flour or sawdust are drawn down by the force of gravity, but they are also acted upon by their own force of cohesion ; and the force of Cohesion is greater than that of gravity. Hence they remain piled up together in a heap. In the case of the water, the force of gravity is much greater than that of cohesion. It draws the molecules downward, and as they have little cohesion, they do not resist, but roll and tumble one over the other, until the surface is level. V. WATER ALWAYS TRIES TO FIND ITS OWN LEVEL Pour some water into a I) tube. Show that as the water is poured down one arm, it rises in the other. It will rise until it stands at exactly the same height in both arms. Show the same thing with a teapot or watering-can. Tilt the pot and so alter the level of the water in it, and the level is also changed in the spout. Water will find its level. Tell how this principle is turned to account in making fountains. All that is required is a cistern of water in some elevated position with a pipe leading from it to the ground, the lower end of the pipe being bent upwards. The water will flow down the pipe, and at the lower end rush upwards in a jet, trying to rise again to the same level as the cistern from which it flowed. It is on the same principle that towns are supplied with water from the water-works. The reservoirs are placed on elevated ground, and the water which leaves them rushes on, trying to find the level from which it started. 140 OBJECT LESSONS Show a spirit-level, and tell of its uses. Why should alcohol be used for this purpose ? It is a very mobile liquid. VI. LIQUIDS WILL NOT BE SQUEEZED INTO A SMALLER SPACE Fill a squirt or syringe with water, and close the hole firmly with the finger. Now try to force down the piston. It will not move. The water refuses to be squeezed into smaller space. Fill a, bottle to the top of the neck with water, and then try to push a cork into it. You can only force the cork in by forcing some of the water out, to make room for it. The water refuses to be squeezed. We say liquids are incompressible. Lesson VI PRESSURE OF LIQUIDS I. LIQUIDS PRESS DOWNWARDS IF I take this brick in my hand, I know it presses downward. Why ? Because it feels heavy when I try to lift it. If I fill a jug with water, I also know that the water presses downward, for I find that the jug is heavier than it was when it was empty. Put the brick into this box. Its whole weight is pressing on the bottom, it does not even touch the sides. Place another on the top of this, and a third on that, and note that each time the downward pressure increases. The top brick presses upon the one below, and this transmits the pressure to the bottom of the box. LES. vi PRESSURE OF LIQUIDS 141 Now we will remove the bricks and pour water into the box. Show that as the water rises the downward pressure increases. The upper layers of water (like the upper bricks) press upon those below, and they transmit or send the pressure through to the bottom of the box. II. LIQUIDS PRESS SIDEWAYS We will next bore a hole in the side of the box. The water runs out in a stream. Plug up this hole, and make another on the opposite side. The water flows out through this hole too. Do the same on the other side, and show that the water flows out as before. Remove the plugs, and show all the streams flowing sideways in various directions. Now what does this prove? That water presses sideways as well as downwards. The upper layers of water press on those below, and they transmit the pressure (not only downwards) but also sideways. What is true of water is true of all liquids. III. LIQUIDS PRESS UPWARDS Lay a broad, flat piece of light wood on the water, and call upon one of the boys to come and press it down below the surface. It is not easy to do this. Why ? Because something seems to force it up. Take a glass cylinder and tie over it at one end a piece of bladder, leaving the bladder to hang loosely down like a sort of bag. Plunge this end of the cylinder into water, and the bladder will be forced upwards and inwards into the cylinder. Take the same glass cylinder and cover one end of it with a light metallic disc, suspended from its centre by a string which passes up through the cylinder. 142 OBJECT LESSONS STAND, iv Lower into the waiter^ "keeping the disc dose by means of the string. Release the string and show that the disc does not fall away, but remains pressed against the lower end. Thus the bladder and disc are pressed upwards by the water. Liquids therefore press in all directions. IV. LIQUIDS TRANSMIT PRESSURE EQUALLY IN ALL DIRECTIONS We have seen that liquids press downwards, upwards, and sideways. Let us go a little farther. Here is a hollow india-rubber ball. We will fill it with water. What happens when I press it ? The water squirts out in a stream through the hole. Why 1 I will tell you. The pressure applied by my hand is conveyed or trans- mitted through the water towards the hole in the ball. Now we will fill the ball again ; but this time I am going to pierce it with a needle in a great many places. I close the big hole with my finger, and then give the ball a sharp squeeze. What happens? Little streams of water flow out through the needle-holes in all directions. What does this show ? That the water transmits equally in every direction the. pressure which I applied by my hand. Lesson VII PRESSURE OF LIQUIDS continued I. PRESSURE INCREASES WITH DEPTH (a) The downward pressure. This we showed just now. The more water we poured into the box the heavier it became, i.e. the greater the downward pressure became LES. vii PRESSURE OF LIQUIDS 143 (b) Pressure sideways. Take a long, round cardboard case. Close one end with a bung or plug of some sort, so as to make it water-tight. We have now a tall vessel capable of holding water. Fill it. If I bore a hole in the side, of course the water will flow out. Now notice I will bore several holes, one below the other. The water flows out through each. But are all the streams alike ? Let us look at the top and bottom ones. The top one flows gently compared with the rush of the bottom one, and each one, from the top downwards, flows with greater force than the one above it. Now what does this prove ? That the pressure of a liquid sideways increases with the depth. Tell that in constructing reservoirs, canals, etc., it is necessary to make the walls or banks thicker at the bottom than the top, because the greater the depth the greater the sideway pressure. (c) The upward pressure. We will return now to our glass cylinder and disc. Lower the cylinder a little way, and let go the string. What is it that keeps the disc close to the cylinder ? The upward pressure of the water. Now pour water gently into the cylinder until the disc falls away. Note what amount of water stood in the cylinder at that moment. It required the downward pressure of that amount of water in the cylinder to overcome the upward pressure on the disc. Lower the cylinder again, but to a greater depth, and show that more water is now required to detach the disc. Hence the greater the depth the greater the upward pressure. Thus we see the pressure downwards, upwards, and sideways in all directions increases with the depth. II. AT THE SAME DEPTH THE PRESSURE is EQUAL IN ALL DIRECTIONS Return to the cardboard case. First plug up all holes. 144 OBJECT LESSONS STAND, iv Now pierce a cirde of holes at the same level, and fill with water. Show that equal streams flow from all with equal force. Repeat at intervals farther upwards, keeping the cylinder filled in each case. At the same depth the pressure downwards and sideways is equal. Lower again the cylinder and disc to a certain depth in the water, and let go the string. Tlie disc does not fall away. Move it horizontally through the water. No change in the disc. The pressure upward is the same at that depth. Raise it ever so slightly, and the disc falls because the pressure is not so great there. Repeat at lower depths and with water in the cylinder, and show that it is always the same. At the same depth the pressure upward is always equal. Lesson VIII BUOYANCY OF LIQUIDS I. SOLID BODIES WEIGH LESS IN WATER THAN IN AIR SUSPEND a small square block of flint-glass from a string, and lower it into a vessel of water. Make the class apply to the immersed body all they have learned about the pressure of liquids. Lead them to see that the side pressures are all equal and balance each other. The block does not move right or left. We need now only take account of upward and down- ward pressures. Make the children show how these act. Which is the greater, and why 1 But you can tell of another downward pressure besides that of the water on top of the block. The pressure of gravity or the weight of the block itself. Let us find out what this is. LES. vni BUOYANCY OF LIQUIDS 145 Remove it from the water and weigh it. Our piece of glass weighs 3 oz. ; so then, when we lower it in the water, it presses downward with a weight of 3 oz. Now I am going to take away the scale -pan and suspend the piece of glass from the arm of the balance. It still weighs 3 oz. Now I will lower it into the water. What do we see 1 The scales will not balance. The glass does not weigh 3 oz. in the water. Let us see what it weighs. Show that instead of 3 oz. it will only weigh 2 oz. Explain what this means. The piece of glass is pressing downwards with a force of 3 oz., but the water is pressing upwards, and it is this upward pressure of the water which seems to rob the glass of $ of its weight. The principle may be illustrated with a piece of brick or sulphur. Each of these substances loses half its weight when suspended in water. Now if I detach the piece of glass, brick, or sulphur from the string, what will happen to it 1 It will sink to the bottom. Show that it does. Why does it sink? The downward pressure of its weight is greater than the upward pressure of the water. All solid bodies weigh less in water than in air, but some, such as stone, iron, lead, and other metals, sink to the bottom if unsupported. We call them heavy bodies. II. FLOATING BODIES Place in the water blocks of cork and one or two different sorts of wood, e.g. oak, beech, and white pine. Note that these rest on the surface of the water. Let one of the children try to force them down to the bottom. What is the result ? They immediately rise to the top again. Let them try to do the same with a bladder filled with air. VOL. II L 146 OBJECT LESSONS STAKD. iv It is not at all an easy matter to force this under water, and as soon as they let go it springs up to the surface again. As they press U down they feel the water pressing up. The water tries to bear or buoy it up. It tried to do the same with the piece of glass, 'but it was too heavy, and its weight overcame the upward pressure of the water, so that it sank. We call this upward pressure of the water its buoy- ancy. By this we mean its power of bearing or buoying bodies up, and making them rest or swim on its surface. Bodies which rest or swim in this way are said to float. But why do they float ? They float because the upward pressure of the water is greater than their downward pressure or weight. Call attention to the way in which the various bodies float. The bladder rests lightly on the water, the cork sinks into it a little way, the pine, beech, and oak woods sink lower down. Now what does this mean 1 Take a vessel with a hole in one of its sides, and fill it with water up to the hole. Now take the piece of glass which we used just now and lower it into the water. What happens? Some of the water runs out of the hole into the basin below. Why does it run out ? Because it must make room for the glass. The glass as it dips down forces out exactly its own bulk of water, for the water and the glass could not occupy the same space. Now if we collect this water and weigh it, we shall find it weighs just 1 oz. But 1 oz. was exactly what the glass lost in weight in the water. That is to say, the upward pressure of the water is equal to the actual weight of the quantity of water which the body displaced. If now we put into the water some body equal in weight to its own bulk of water, it would float with its upper LES. ix PRESSURE OF THE ATMOSPHERE 147 surface on a level with the water. It would in fact displace a quantity of water equal to itself, bulk for bulk. Our piece of oak floats, but its upper surface is a little way above the water. The beech wood floats too, but higher than the oak ; the pine wood higher still ; the cork still higher ; while the bladder filled with air simply rests on the water. A piece of iron or tin sinks in the water because it weighs much more than its own bulk of that liquid. But I put this canister in the water and it floats. Why is this ? Lead the class to discover. It is made of " tin " (i.e. iron coated with tin), but being hollow and filled with air only, it weighs much less than its own bulk of water, and the water can thus bear it up. This explains why our great iron ships float on the sea. They are lighter than the water, bulk for bulk, and the buoyancy of the water makes them float. Lesson IX PRESSURE OF THE ATMOSPHERE I. AIR HAS WEIGHT THE air all around us is, as we have seen, a material sub- stance or gas. It surrounds our earth and covers the tops of the highest mountains. We, in fact, live and move about at the bottom of an ocean of air just as fishes and other animals do at the bottom of the sea. This ocean of air, being a gas, has no surface. It ex- tends far beyond the mountain tops probably fifty miles upward perhaps beyond that. People who go up in balloons find the air gets thinner as they ascend, until it becomes very difficult and at last quite impossible for them to breathe. Tell that the greatest height ever reached in a balloon was seven miles. 148 OBJECT LESSONS STAND, iv Picture a pile of feather-beds placed one upon another and extending upwards for miles. They might all be made of the lightest down, but those at the bottom would be packed close and dense by the weight of those above. The weight or pressure of the layers above is transmitted to the lower layers. It is just so with the air. This, being a material sub- stance, has weight. That is to say, every particle of air is attracted or drawn down to the earth by the force of gravity. The layers above press upon those below, so that the air at the foot of a mountain or near the sea-level is always denser and heavier than that at its summit. Refer to our late lessons on liquids, and compare what was said as to the pressure of water at the bottom and near the surface. So then air, like water, is a material substance and has weight. Tell how we can actually weigh a quantity of air, by exhaust- ing the air from some vessel, and then weighing the vessel both empty and when full of air. The actual experiment is best shown after the air-pump has been explained. If we take a square box measuring a foot each way, we shall find that the air in it weighs rather more than 1 oz. A cubic foot of air on the side of a mountain would not weigh an ounce, and it would weigh less still at the top. Why ? Because as we ascend the air becomes lighter and thinner ; it has less weight to support above it. II. THE AIR PRESSES EQUALLY IN EVERY DIRECTION Show a boy's leather sucker. Make the class describe it ; say how it is made and how it is used. You have often seen boys play with the sucker. Let us play with it now. LES. ix PRESSURE OF THE ATMOSPHERE 149 We will first soak it in water to make it soft and flexible, and then press it on the hearth-stone. If now I pull the string, I shall find that the leather holds firmly to the stone as though it were stuck to it. It is not stuck to the stone as we have seen some things stuck together, for leather, whether wet or dry, is not an adhesive substance. Show that leather does not adhere to other substances. There is another way to make two things hold together. Suppose I lay this card on the floor and stand this heavy weight on it. Could you pull the card away with a string ? No. Why not 1 Because the weight presses it down. But what has this to do with our sucker ? Let us see. When I put the sucker on the stone I pressed the leather well. I did that in order to squeeze out all the air from between the leather and the stone. There is nothing between them, not even a little air. There is air outside, but none under the sucker. The sucker is held fast to the stone by this outside air pressing down upon it, just as the weight presses down upon the card. Repeat the experiment with a slate held in various directions horizontally, slanting, vertical, overhead. Show that in every position the sucker holds fast to the slate. Even when we hold the slate overhead and pull the string downward the sucker holds firmly. But we found out why the sucker clung to the hearth- stone. The air all round pressed it close to the stone. We have seen that the sucker adheres equally close to the slate in whatever position it is placed. Hence it is the pressure of the air in every case which makes the sucker hold fast to the stone or slate. If this is so, what have we found out ] That the air presses equally in every direction, for it did not matter in the least how we placed the slate the sucker still held on. 150 OBJECT LESSONS STAND, iv The air in this room is pressing equally on floor, walls, and ceiling ; that is to say, in every direction. Call attention once more to the sucker. It is still clinging fast to the slate. Try and pull it away. It will not move. Now bore a small hole through the leather, and let the class note the result. Why does the sucker become detached now ? Tell that air rushed through the little hole immediately it wa& made, and this air pressed upward on the under side of the sucker with as much force as the outer air was pressing down- wards, and thus the sucker was released. Fill a tumbler with water, and cover with a card or piece of paper, pressing the paper dose to the rim of the glass. Now invert the tumbler. When the hand is removed the paper will not fall. The water will not run out. Why ? The air presses upwards on the paper and holds it close to the glass, so that the water cannot fall out. Note that this pressure of the air must be considerable, for the water in the tumbler is heavy and would naturally fall if un- supported. Next take the tumbler, inverted as it is, and place it in a basin of water with the lower end just below the surface. Gently remove the card. What do we see? The water still stands in the tumbler although there is no card below it now to keep it in. What is there below it ? The water in the basin. Why does it not rush out and push this water away ? The air is pressing downwards on the surface of the water in the basin, and this downward pressure is transmitted in all directions by the water itself. The result is that the water in the basin exerts an upward pressure upon the water in the tumbler, and prevents it from running out of the tumbler into the basin. LES. x WEIGHT OF THE ATMOSPHERE 151 Let us now see what we have learned. 1. Air has weight, and presses equally in all directions. 2. The weight of the air, and consequently its pressure, varies with the height the densest and heaviest air and the greatest pressure being near the sea-level. Lesson X WEIGHT OF THE ATMOSPHERE I. INTRODUCTION REFER to the experiment with the inverted tumbler in the basin of water. Make the class describe what took place, and why. Repeat it now, using a long glass test-tube instead of a tumbler. The result is the same. The water stands in the tube, held there by the downward pressure of the air on the surface of the water in the basin. Any other liquid will do equally as well as water. Repeat with mercury, using a small test-tube. The mercury stands in the tube just as the water did, and for the same reason. It is held up by the downward pressure of the air. Now take a much longer glass tube, say a yard in length. It must be closed at one end, and should have a small bore. Fill with water and invert as before. None of the water flows out. Now remove the tube, pour out the water, and replace with mercury. Wlien full, invert the tube in the usual way, and stand it in a vessel of mercury. AYhat has happened ? Some of the mercury has run out of the tube into the vessel. There is no mercury in the top part of the tube. 152 OBJECT LESSONS STAND, iv What is there then ? Air ? There can be no air in that upper space, because we filled the tube with mercury, and the mercury has simply dropped down. It is an absolutely empty space. We call it a vacuum. Let us see whether the mercury will fall any lower in the tube. No, it will not move, even if we shake the tube, so long as we keep the lower end in the vessel of mercury. If we take it out, all the mercury at once runs down the tube, but if we refill it and invert it again in the vessel of mercury, the mercury will stand at the same height as before. If we measure the height of this column of mercury from the top to the level of the liquid in the vessel below, we shall find it to be as nearly as possible 30 inches. Now we must ask ourselves two questions 1st. Why the mercury stands in the tube at all ? 2nd. Why it stands at 30 inches ? IL WHY THE MERCURY STANDS IN THE TUBE Let us take the first one. We have in the tube a long thin column of mercury 30 inches high. This mercury is a very heavy liquid metal, and its weight presses downward. If it could it would run down the tube into the basin below. As it does not run out, there must be something to prevent it. Let us see what that something is. Try and picture (for we cannot see it) a very long", tall column of air of exactly the same thickness as the mercury in the tube, but reaching many miles upwards to the very extreme limit of the atmosphere. Imagine if you like that this long thin column of air is contained in a tube reaching all the way up from the surface of the mercury in the basin. LES. x WEIGHT OF THE ATMOSPHERE 153 This long column of air then presses downwards, by reason of its own weight, upon the surface of the mercury in the basin. What else did we say is pressing down upon it as well as this column of air t The mercury in the tube is also pressing down upon it ; it is trying to get out of the tube and cannot. The downward pressure of the air prevents it. The column of air and the mercury in the tube press downwards with equal force and balance each other like two equal weights in a pair of scales. III. WHY THE MERCURY STANDS AT THIRTY INCHES Now you can answer the second question yourselves. Why does the mercury stand at 30 inches ? The column of mercury 30 inches high weighs exactly the same as the long column of air, and so the two balance each other. Explain now what is meant by a square inch. Draw a square inch on the black-board. Show, if possible, a tube 30 inches high with a base of a square inch. Imagine this filled with mercury, and tell that such a quantity of mercury would weigh just 15 Ibs. Now, if our tube had been as big as this one, our column of air pressing downward on the surface of the mercury outside must also have been a square inch in section ; that is to say, it must have covered a square inch of the mercury in the basin. What do we learn, then, from this ? That the pressure of the air on a square inch of surface would be balanced by a column of mercury weighing 15 Ibs., i.e. that the air presses with a force of 15 Ibs. on every square inch of surface. IV. PRESSURE EQUAL IN ALL DIRECTIONS Show a slate say 10 inches by 8. This contains 80 square inches. 154 OBJECT LESSONS SFAND. iv Calculate the pressure upon this slate eighty times 15 Ibs. or upwards of half a ton. But a baby could lift the slate. It is not heavy. Why is this 1 There is not only that enormous pressure on the top of the slate, there is an equal pressure from below and all round. Think what must be the pressure upon this table. But the table is not crushed. Why not? Because there is also an upward pressure of equal force to balance it, and it is not felt. Every child goes about with many tons pressing upon his body, but he never feels it, because there is air inside his body too and this presses outwards and balances the pressure on all sides of him. We shall be able to understand now why our sucker held fast to the stone. Suppose the sucker measured 6 sq. in. There would then be a force or pressure of 6 x 15 Ibs. = 90 Ibs. press- ing it to the stone. We felt that pressure when we pulled the string, because there was no upward pressure between the stone and the leather to balance it. The pressure of 90 Ibs. on the top of the sucker pressed the sucker and the stone firmly together, and we could not move them. When I bored the hole in the leather, however, and air rushed in, we had the same force of 15 Ibs. on every square inch of the under surface, and the sucker let go the stone the two pressures balanced each other. Lesson XI THE BAROMETER I. INTRODUCTION LEAD the children to talk about the experiment shoum in the last lesson with the tube of mercury. LES. xi THE BAROMETER 155 Make them tell how it was done, and why the mercury stood in the tube instead of falling into the basin. Keep up the idea of a balance or pair of scales the column of air on one side, the column of mercury on the other both pressing downwards on the mercury in the basin neither able to force the other aside. They balance one another. Repeat the experiment, now making the class explain step by step. The mercury in the tube measures the pressure of the air on the surface of the mercury in the basin. Now I have here a pair of scales. Let us weigh some- thing. We put our object (whatever it may be) into one scale, and then we must put certain weights into the other scale to balance it. When we have done this, we say we have weighed the thing, and can tell its weight. But suppose I put something into the object scale in addition to the first thing. What else must I do ? Put more weights into the other scale or they will not balance. The weights in the one scale measure the downward pressure of the object in the other scale. Now our tube of mercury is another balance. What is the object to be weighed ] The air. What does duty for the weights 1 The mercury in the tube. What does the mercury measure 1 The pressure of the air on the surface of the mercury in the basin. But suppose the pressure of the air increased. What would happen then 1 The increased pressure of the air on the surface of the mercury in the basin would force more mercury up into the tube. The mercury would be said to rise in the tube- the column would be higher, and, of course, heavier than it was. There would be a greater weight of mercury in the tube to balance the greater pressure of the air. Follow up the same reasoning, and show that if the pressure 156 OBJECT LESSONS STAND, iv of the air decreased, the mercury would fall in the tube, because it would not require so great a weight of the metal to keep the balance. II. THE WEIGHT OF THE ATMOSPHERE VARIES We have just been inquiring what would happen to our column of mercury if the pressure of the air became greater or less than it is at present. I am now going to show you that this is not a mere supposition, for the pressure of the air is not always the same. 1. It varies with the height above the sea-level. You know that, as we climb up a mountain or sail up in a balloon, we leave all the dense and heavy air below us. The higher we ascend, the thinner and lighter the air becomes. Let us take our mercury-tube up with us. If we look at it after we have ascended 1000 feet, we shall find the mercury has fallen one inch, and it would continue to fall at the same rate for every 1000 feet we ascended. On the top of Mont Blanc, 15,000 feet high, the mercury in the tube would stand only about 15 inches high, and would weigh 1\ Ibs. instead of 15 Ibs. What does that tell us ? That the pressure or weight of the air at that height is only half what it is here to-day. If, on the other hand, we take our mercury-tube down into a coal-mine, we shall find that the lower we go the higher the mercury will rise. Roughly speaking, we may say it rises 1 inch for every 1000 feet we descend. What does that tell ? That the weight of the air in the mine increases as we descend. 2. It varies according to the quantity of vapour it contains. The air always contains more or less vapour, because evaporation is always going on to a greater or less extent. LEA xi THE BAROMETER 157 What becomes of this vapour ? It rises in the air and forms clouds. If it rises in the air, which is the lighter body ? Vapour is lighter than air. Air, then, which contains much moisture is always lighter than air which is drier. The vapour actually takes the place of some of the air. Dry air is heavy ; moist, damp air is light. Now how would the condition of the air affect our mercury-tube ? When the air is dry and therefore heavy, it presses with greater force on the mercury in the basin, and must then be balanced with a taller and heavier column of mercury in the tube. When the air is saturated with vapour and is therefore very light, the pressure is less and the column of mercury in the tube balancing it will accordingly fall. III. THE BAROMETER AND ITS USES We have all this time been talking of a very wonderful instrument, although I have only spoken of it as the tube of mercury. We see that the tube of mercury, as we call it, measures exactly the pressure or weight of the atmosphere. I am going now to call it by another name which means all this. Its proper name is barometer a word which means the weight-measurer. Our tube and basin of mercury really formed a baro- meter, although they would be very awkward to carry about from place to place. All that is necessary for a barometer is a glass tube, closed at the upper end and of equal bore all through, with a cistern or reservoir at the lower end. The tube is usually made thirty-three inches in length, and the cistern at the bottom has one opening through which the air can enter. For the sake of safety the tube and cistern are usually fitted into a frame, and the height of the column is 158 OBJECT LESSONS STAND, iv marked on the frame or glass in inches. The marking, for general purposes, commences at twenty-seven, and ends at thirty-one inches. 1. Its use in measuring heights. The barometer tells us the height of mountains. We have only to read the barometer at the foot of the mountain and again at the top, and then reckon on 1000 feet for every inch difference in the mercury, and we know approximately the height of the mountain. 2. Its use as a weather-glass. We have seen that the barometer tells us two things: (a) The weight of the atmosphere. (b) Its condition (moist or dry) from the amount of vapour it contains. If we kept a barometer in one place, and watched it carefully from day to day, we should find that the mercury would rise and fall in the tube, sometimes reaching to nearly thirty-one inches, sometimes falling to twenty- eight inches. When the mercury in the barometer falls, what does it mean ? That the air is getting lighter. What makes the air lighter 1 ? The large quantity of water-vapour it contains. But if the air contains a large amount of vapour, we know we are likely to get rain and stormy weather, for the air is being loaded with more vapour than it can hold. In the same way, when the mercury in the barometer rises, we know that the air is heavier, and therefore drier, and we have a prospect of fine weather. Most barometers are furnished with a dial-face marked with the various changes in weather, from stormy and rain to fair and very dry. Show, if possible, one of these, and illustrate by means of a diagram the working of the hands. LES. xii THE SYRINGE 159 Lesson XII THE SYKINGE I. INTRODUCTION TAKE a glass tube, open at both ends. Place the finger firmly over one end, fill the tube under water, and invert it, still keeping the open end below the surface. The water Stands in the tube. Make the class tell why ? The pressure of the air on the surface of the water in the basin forces back the water in the tube, and prevents it from running out. Remove the finger from the top of the tube, and the water runs out at once. Why is this ] There is air now pressing on the water in the tube with the same force as that which presses on the water in the basin. One pressure balances the other, and the water in the tube rests level with that in the ,basin. Let a boy come and suck the upper end of the tube. The water rises into his mouth. Who can tell why ? He does not suck up the water itself. By sucking he removes the air which fills the tube, so that there is no longer any air within it to press down the water at its lower end. But he cannot remove the air outside the tube. That is still pressing on the water in the basin. Instead, therefore, of having two equal downward pressures, one inside and one outside, balancing each other, we have now only one, and it is this pressure of the air outside which forces the water up the tube into the boy's mouth. We can prove that the boy did not suck up the water itself. Here is a bottle filled with water. The cork fits very close, and I have fitted a glass tube through a hole in the cork. 160 OBJECT LESSONS STAND, iv Now I will press the cork tightly into the neck of the bottle, and some one shall come out and try to suck up the water as before. He now finds it impossible to draw the water up into his mouth. Let us see why this is. The sucking removed the air from the tube as before. Why does the water not rise ? The bottle is quite full of water ; there is therefore no air above it to press down on its surface, as there was in the other experiment, and so force the water up the tube. In the first experiment, then, the water is not sucked up, it rises in the tube by the pressure of the air all round. II. THE SYRINGE Show a common squirt or syringe a glass one mil be best. Prepare a little coloured water. Now I am going to show you how we can raise water by means of this instrument, but first let us have a look at the instrument itself. Take the syringe to pieces, and let the children examine it. It is simply a tube with a rod, which we call the piston, fitting it closely all round, so that no air can pass between them. We say it fits the tube air-tight. Now I will dip the end in this coloured water, and pull up the piston-rod. What takes place ] The water rises in the syringe. Why does it rise ? That piston sucks up the air, so as to form an empty space or vacuum above the water. The pressure of the air on the water outside forces the water up into the tube to fill up this vacuum. The water rises, then, in the piece of glass tube and in the syringe from the same cause. The air above it is first sucked up or removed. LES. xni THE SUCTION-PUMP 161 In the one case we suck it up by the mouth, and in the other it is the piston which does the sucking. Press the piston back, and show that the pressure drives out the water in a stream. Tell the uses of the instrument. Lesson XIII THE SUCTION-PUMP I. INTRODUCTION I DARE say you have often seen water raised by means of a pump. Let us next try and find out why the water rises in the pump. First of all, where does the water come from 1 It comes from a well. Before pumps were used people had open wells, and drew up the water in buckets. Show a picture of a well with its bucket. A pump is better, for many reasons. The first essential in a pump is a long pipe or tube dipping down into the well. Sketch it on the black-board. This is generally called the SUCtion-pipe. Now here we have the tube, and here is the water all round it, and we know that there is air both in the tube and above the surface of the water outside. This air is always pressing downwards with the same force, and thus the water in the tube is kept at the same level as the water in the well. Think now of our glass tube, and how we made the water rise in it. We first removed all the air from the tube. This is exactly what we must do with the pump, or the water cannot rise. VOL. II M 162 OBJECT LESSONS STAND, iv II. CONSTRUCTION Closely fitted to the upper end of the SUCtion-pipe is a wider tube the barrel. Follow up the sketch on the black-board step by step. The entrance from the suction-pipe into the barrel is guarded by a little door which works on a hinge and opens upwards only. A door of this kind allows a fluid to pass in one direction, but prevents it from returning. Such a door we call a valve, and this is known as the suction-valve. Show the valve of a pair of bellows, and explain its working. It is very similar to that mostly used in the common pump. In the barrel itself is fitted an air-tight piston, capable of being moved up and down by a piston-rod which is worked by a handle. A spout opens on one side of the barrel. In the centre of the piston is another valve similar to the suction-valve, and, like it, opening upwards only. This is called the piston-valve. There should now be a complete sketch on the black-board of the whole contrivance. III. WORKING // would be well, if possible, to show a small glass model of the pump here. Remind the children again that the suction-pipe is full of air from the surface of the water upwards. The whole object of this contrivance is to remove the air, and so allow the water to rise in the pipe. Let us set our machine to work. Imagine that at the commencement the piston has been forced down and made to rest upon the suction-valve in the bottom of the barrel. Both valves are closed. There is no space, and consequently no air between. Now gradually raise the piston by lowering the fiandle. LES. xiii THE SUCTION-PUMP 163 There is of course air above the piston, and as the piston rises this air forces down its valve and quite closes it. But what has been happening at the suction -valve meanwhile 1 The raising of the piston (with its valve closed) has made an empty space or vacuum in the barrel, and the air in the pipe below has forced open the suction- valve and rushed through to fill up the space. There is therefore less air in the suction-pipe than there was there is not the same pressure on the water within the pipe. But the air outside is pressing on the water in the well with the same force as ever. There is the same 15 Ibs. pressure on every square inch, and this outer pressure forces the water to rise some distance in the pipe. Now lower the piston by raising the pump-handle. As the piston descends it presses upon the air below it in the barrel, and this air forces up the piston-valve and escapes through it. But why does the air not return down the suction-pipe again ? It cannot. The first result of lowering the piston and pressing it down upon the air is to close fast the suction-valve. The piston and suction-valve are now close together as they were at first. We raise the piston again as before. This time more air, probably the whole of it, is exhausted from the suction- pipe. If so, the water rushes up through the suction-valve and fills the barrel. When we lower the piston again it is water which forces its way through the piston-valve, and by the time the piston has reached the bottom of the barrel again, we have a continuous column of water from the bottom of the pipe upwards. liaise the piston once more. The weight of the water above closes its valve, and that water is carried up to the spout, whence it runs out in a stream. The raising of the piston has again filled the barrel, and the stream will now be continuous. 164 OBJECT LESSONS STAND, iv Lesson XIV OTHEE PUMPS I. LIMIT TO THE RAISING POWER OF THE COMMON , PUMP REFER to the experiment with the tube of mercury which was shown in connection with the lesson on the atmosphere. Make the children tell all they can about it. What is the height of the mercury in the tube ? What causes it to rise in the tube 1 What causes the water to rise in our pumps 1 Now if we used the pump to raise, not water, but mercury, how high do you think we could lift the mercury by pumping 1 The mercury, like the water, would rise through the pressure of the atmosphere only ; and it would be im- possible to raise it higher than 30 inches. Make the class tell that a column of mercury 30 inches high and a square inch in section weighs 15 Ibs., -and this exactly balances the pressure of the atmosphere on the square inch. Tell that we might have used water in the tube instead of mercury for our experiment ; but that water is 13 J times as light as mercury, and it would have required therefore 13 times more water to balance the weight of the air. Our tube must have been long enough to hold 30 x 13 J in. = 34 ft. of water. Lead the class to deduce this for themselves. You see now why we used mercury instead of water. But if we had such a tube filled and inverted in a vessel of water, the column of water in it would reach nearly 34 ft. in height. Why 7 Because 34 ft. of water weighs exactly the same as 30 in. of mercury, and exactly balances the pressure of the air. LES. xiv OTHER PUMPS 165 Now can you tell me how high we can raise water by means of the pump ? Nearly 34 ft. It ought to rise to that height, but does not because it is impossible to obtain a perfect vacuum unless the pump is constructed with the greatest care. The greatest height with an ordinary pump is 26 or 28 feet. II. THE LIFTING PUMP Draw a sketch of this in section on the black-board. Show that the main difference between it and the common pump is that the piston of this one is solid and has no valve. Near the bottom of the barrel is a discharge pipe, which bends upwards, and is provided with a strong valve opening outwards, to allow water to pass out from the barrel, but to prevent its return. The working may be explained from the sketch. It will lift water to almost any height. III. THE FORCE-PUMP Draw a section on the black-board as before. Show the points of similarity between it and the last. The great difference is that in this machine the pipe leading from the barrel opens into a condensing 1 chamber. The entrance into this chamber is guarded by a strong valve opening upwards, and the walls of the chamber are of great strength. The discharge pipe dips down into the chamber and passes upward into the air. This pipe has no valve. As in the case of the lifting pump, the piston in descend- ing presses down on the water in the barrel, closes the suction-valve, and drives the water through the horizontal pipe. At each downward stroke of the piston, then, more water is driven along the pipe through the valve and into the condensing chamber. 166 OBJECT LESSONS STAND. i\ This chamber is full of air, and as the water rushes in, the air is very much compressed. The rest is a struggle between the compressed air and the water which is still being forced in. The air presses down on the water ; but water cannot be compressed into smaller bulk. The water cannot return by the way it came, partly because of the valve, and also because of the body of water behind. There is one way of escape up the discharge pipe ; and up that pipe it rushes in a continuous stream. IV. THE FIRE-ENGINE Draw a sketch. Show that this machine is really a double force-pump. There are two pipes, one from each pump, opening into a central condensing chamber, from which the delivery hose passes. A strong hose from the bottom of each pump is attached to the water-supply, and as the pumping goes on the water is raised through these pipes into the barrels of the pumps, and passed from the barrels into the common condensing chamber, whence it is sent out in a continuous stream through the delivery hose. Lesson XV THE AIR-PUMP THE pumps we have examined are employed for pumping liquids. We are now going to study a machine for pumping air. We call it the air-pump. I. CONSTRUCTION This machine consists of two parts a pump and a receiver. LES. xv THE AIR-PUMP 167 Draw a sketch on the Hack-board as the description proceeds. 1. The pump. The pump is very similar in con- struction to our common pump. It is formed of brass, and every part is most carefully made and fitted. It has a tube or barrel in which an air-tight piston, worked by a piston-rod, moves up and down. The piston itself is furnished with a valve opening outwards, and there is at the bottom of the barrel another valve opening in the same direction. What is the object of valves ? How do they act 1 They allow fluids to pass readily in one direction, but prevent them from flowing back again. The first attempt the fluid makes to flow back shuts the valve, and the way is closed. This is exactly the construction of our common pump. Below the barrel is a brass pipe leading from the pump to the second part of the machine the receiver. This pipe is furnished with a close-fitting stop-cock. When the cock is turned on, the way along the pipe is open ; but it can be turned off, and so closed, and when that is done not a particle of air can find its way through. 2. The receiver. This is simply a large glass bell, which fits closely and exactly on a brass plate. It is called a receiver because it has to receive any substance with which we may have to deal. In the brass plate is a hole into which fits perfectly air-tight the pipe leading from the barrel of the pump. There should now be a complete sectional sketch on the black- board. II. WORKING Let us imagine that we have an actual machine ready to work. Before commencing to pump you must remember that the receiver and the pipe leading from it are full of air. Our object is to remove the air by pumping it out. 168 OBJECT LESSONS STAND. IY We will commence pumping with the piston close down on the suction-valve at the bottom of the barrel. That valve is quite closed, and so is the piston-valve above. Now when we raise the piston the pressure of the out- side air closes its valve, and all the air above is forced out through the upper part of the barrel. But what else has been going on 1 The raising of the piston has made (or tried to make) a vacuum above the suction-valve. Now I want you to think of the principal properties of air and all gases. There is no cohesion of particles. They spread themselves out from each other so as to fill the greatest possible space. Let us see what that has to do with the air-pump. When the vacuum is made in the barrel of the pump, the air in the receiver and the pipe leading from it ex- pands so as to fill a greater space. It thus forces open the suction-valve, fills the barrel again, and there is no vacuum. We will now force the piston down again. The first movement downward compresses the air in the barrel and shuts the suctibn-valve. But the compressed air forces open the other valve as the piston descends and makes its escape above the piston. The next upward and downward strokes of the piston repeat exactly what has been already done. This goes on until the air in the receiver has so ex- panded that it has become thinner and thinner, and at last it is so thin and feeble that it is not able to force open the suction- valve. We then say that the air has been exhausted from the receiver. This is as far as we can get, although it is not absolutely emptied of the air it contained. It still contains a little air, but it is exceedingly thin and rarefied. Point out that, before the experiment, we could easily lift the receiver off the plate. L. xvi HOW HEAT AFFECTS DIFFERENT SUBSTANCES 169 Let some one try now to lift it. He cannot. WTiy ? Tell that before we commenced to pump there was air inside as well as outside the bell and the pressure was equal. We had only to lift the weight of the glass itself. Now there is only a very small quantity of highly rarefied air inside the bell, but the outer air is still pressing with a force of 15 Ibs. on every square inch. Imagine the tons which are pressing upon the glass bell. It is this pressure which holds it so firmly to the brass plate. LESSONS ON HEAT Lesson XVI HOW HEAT AFFECTS DIFFERENT SUBSTANCES I. INTRODUCTION HOLD a piece of metal in the flame of the spirit-lamp. After a time remove it and place it on a tray or a plate in front of the class. We could not take it up in our fingers. Why? Because it is hot. It was heated in the flame. Now lift it with the tongs and plunge it into a vessel of cold water. Let one of the boys next take it out of the water with his hand. It has less heat than it had ; it is only warm noAV. Place it in some ice, and let the same boy take it out and tell what he observes. It is very cold now. Explain that what he really means to say is, that the metal has less heat still now. There is actually no such thing as cold. Wlien we speak of cold, we mean absence of heat. 170 OBJECT LESSONS II. HEAT EXPANDS BODIES 1. Solids. Take a short round bar of iron, which fits exactly into a hollow metal groove, and will just pass through a ring. Let the class test it. Heat the bar in the fire, and then show that it is too long and too broad to lie in the groove now, and that it will not pass through the ring. Why is this t The bar is longer and thicker than it was. The heat has made it expand in every direc- tion. Throw it into cold water and try again. It fits exactly now. It fits exactly now, because the heat is removed or taken away. Take a ball of copper or brass and show that it will just pass through a metal ring. Place it in boiling water and try again. It will not now pass through the ring. It is too large. The heat has made it expand. Cool it by throwing it into cold water, and call attention to the fact that it again passes through the ring. It has con- tracted again because the heat has been taken away. What is true of these is true of almost all solid bodies. They expand by heat, and contract when the heat is removed. 2. Liquids. Fill a test-tube quite full of water and apply the spirit-lamp. What happens ? The water swells up and overflows. Repeat with mercury in the same tube. The result is the same. The mercury swells up and would overflow. Why is this? Both liquids expand with heat and require greater space. Show another test-tube which, some time before the lesson, was filled quite full of boiling water. Note that it is not full now. What does this mean ? The liquid has cooled and at L. xvi HOW HEAT AFFECTS DIFFERENT SUBSTANCES 171 the same time contracted. As the heat passed away the liquid contracted into smaller bulk. Take a small flask filled with coloured water and fitted with a cork and a long glass tube passing through it. Press the cork well into tJie neck of the flask. Tlie water will rise a little way in the tube above the cork. Now plunge the flask into a basin of boiling water, and let the class note the result. For a moment the water will sink a little way in the tube, as though it were contracting, but immediately after- wards it will begin to rise, and it will rise very high in the tube. This is curious. Let us try and find out what it means. The heat first affects the glass, and this, like all other solid substances, expands, so that the flask stretches and becomes larger. It is because the flask becomes larger that the liquid at first sinks in the neck, for it has to fill a larger space. Immediately afterwards, however, the liquid itself begins to feel the effect of the heat and expands too. Then we see it rise in the tube, and it rises much higher than it was at first. Therefore it is clear that when the solid and the liquid are equally heated both expand, but the liquid expands more than the solid. Remove the flask from the hot water and plunge it into cold. Note that at first the liquid begins to rise in the tube, but immediately afterwards it begins to sink slowly. Let the class now explain why. 3. Gases. Stand an empty glass retort over the spirit- lamp with its neck in a vessel of water. Let the class tell what they observe. Bubbles of air rise through the water and burst on its surface. Whence did these air-bubbles come ? The flame heated the retort and the air in it, and heated air expands or swells so as to occupy more space. Now remove the flame and allow the retort to cool. Let the 172 OBJECT LESSONS STAND, iv class tdl again what they observe. The water has risen higher in the neck of the retort. WTiy 1 As the air cools in the retort it contracts or shrinks up into smaller space. Some of the air was driven out in bubbles when it was heated, and there is not (now that it has contracted again) enough air to fill the retort. Hence the w,ater rises to fill its place. What is true of air is true of all gases. All gases expand with heat and contract when the heat is taken away. Lesson XVII EXPANSION AND CONTRACTION I. RECAPITULATORY LEAD tlie class to explain what they were taught in the last lesson about heat, and its effect on different bodies solids, liquids, and gases. They should be made to give intelligent accounts of the various experiments that were shown. That of the flask filled with coloured water will afford a good test of their intelligent appreciation of the lesson ; and it ought to be well understood now, because we shall frequently refer to it in later lessons. We have seen that heat causes bodies solid, liquid, and gaseous to expand, and that when the heat is re- moved the bodies contract again to their original bulk. It will be our business in this lesson to learn why this happens. I. HEAT OVERCOMES COHESION Refer to our earlier lessons on fusible substances. Show a piece of iron. LES. xvn EXPANSION AND CONTRACTION 173 It is so hard that we cannot even scratch it. The smith heats it in his forge, and it becomes soft and plastic, so that he can beat, cut, and pierce it, and work it up into any shape he pleases. Why can he do this ? The force of cohesion between its molecules is not so strong now as it was. The heat has overcome the cohesion. It is the same with all metals. What happens to these metals if they are still further heated ? They melt. What does that mean ? They change from the solid to the liquid form. How can you explain this more fully ? The force of cohesion has been still further weakened. The particles are not now held together but are free to move about. The heat has changed the solid into a liquid form. Heat in front of the fire some ice, butter, bees'-wax, palm-oil, sealing-wax, and show that the result is the same. The heat liquefies them. Liquids, as we have seen, expand more than solids. Why is this 1 The force of cohesion in liquids is very slight, and is thus easily overcome. What happens when we continue to apply heat to a liquid 1 The liquid is converted into a gas, the particles of which having no cohesion fly from each other in all directions. The solid ice becomes liquid water the water becomes vapour or water-gas, and all by the applica- tion of heat. Put a piece of camphor in a spoon over the spirit-lamp, and show that in this case heat converts the solid directly into a vapour or gas. TJiere is no intermediate liquid state. Tell that many solids may be converted directly into vapour besides camphor. 174 OBJECT LESSONS STAND, iv III. EXPANSION AND CONTRACTION IN ARTISANS' WORK Workmen often make great use of these expanding and contracting forces in the materials which they use. 1. In fitting the tires on wheels. The tire is made red hot, and while in this expanded state is placed and fitted round the wheel. It is then plunged in cold water. As it cools it contracts and presses the wheel so closely that it not only takes a firm hold itself, but also binds all parts of the wheel together. 2. In building furnaces. The iron bars of the furnace are always left with one end free. If both ends were built fast into the bricks or masonry, their expansion by heat would tear away the brickwork. 3. In fitting the rails of a railway. The iron or steel rails are not placed with their ends close together. There is a little space left between. The rails expand with the heat in summer, and if they were close together the expansion would cause them to bulge and curve. 4. In fitting iron plates. The iron plates of ships and boilers are held together with iron rivets. These rivets are always fastened and fitted red hot, and thus as they cool they by their own contraction draw the plates together with great force. 5. Heated iron bars are often used to draw bulging walls upright. The bars are secured and screwed up while heated, and as they cool they contract and so draw the wall into the proper shape. Lesson XVIII THE THERMOMETER I. HOW TO MEASURE HEAT TAKE three basins, one containing ice-water, another some water from the tap, and a third warm but not hot water from LES. xviii THE THERMOMETER 175 the kettle. Let a boy come to the front and pud one hand in the ice-water and the other into that from the kettle. After a time let him remove them and put both into the tap water. Make him tell the different sensations in the two hands. That taken from the ice-water now feels warm, the other feels cold. A wind which in the heat of summer would appear cool, would in winter be called warm. Two persons meet in the hall of a building on a cold day. The one who has left the warm room feels cold ; the other coming in from the cold outside feels warm. All this proves that our feelings would not afford a true measure of heat. They tell us only relatively. Refer to the teaching of last lesson. Lead the class to tell of the general effect of heat on bodies, solids, liquids, and gases. Set a number of basins side by side, and Jill them with water of different temperature. Now take the flask filled with coloured water and furnished with a long glass tube, and place it in each vessel in turn. Call upon ihe class to note and explain what happens. 1. The water in the flask expands and therefore rises in the tube as it receives the heat. 2. The hotter the liquid into which it is plunged the higher the water rises in the tube. Place it next in some ordinary cold water, and show how the water shrinks and falls in the tube. So, then, by marking carefully the height of the water in the tube each time, we could use our flask and tube as an instrument for measuring the degree of heat. If we were to put our hands into these basins, we should experience sensations of heat and cold, but they would be very deceptive. The flask would give us a rough and ready but true measurement. It is really a simple sort of ther- mometer. Tell the derivation of the word. Therme = heat ; metron = a measure. 176 OBJECT LESSONS STAND, iv II. THE BEST SUBSTANCE FOR MEASURING HEAT What makes the flask and tube a heat-measurer 1 The expansion and contraction of the water inside. But other substances besides water expand with heat, and contract when the heat is taken away. Our bar of iron which we used did so, and almost every solid does the same. Why then would not a bar of iron make a good thermometer 1 ? Solids do not expand sufficiently to be seen and marked. Air and other gases contract too rapidly. We find liquids are the only substances fitted for the purpose. We said just now the flask of water made a rough and rude sort of thermometer. It is rough and rude because it would not suit all purposes. Suppose I had stood the flask in a basin of ice for some time. What would have happened 1 The water inside would have become ice, and have been of no further use for measuring. Or suppose I had placed it over the spirit-lamp ? It would have boiled and become changed into steam or water-gas, and therefore useless again. We have found that the best substance for making a thermometer is mercury. 1. It expands and contracts sufficiently to be seen and marked. 2. It does not change into the vapour state till an exceedingly high temperature is reached. 3. It does not freeze except at a very low tem- perature. Lesson XIX HOW TO MAKE A THERMOMETER SHOW a thermometer, and point out that the essential part of the instrument is a long glass capillary tube with a hollow LES. xix HOW TO MAKE A THERMOMETER 177 bulb or reservoir at one end. This reservoir is filled with mercury, which also rises some distance up the tube. Point out that the tube and reservoir are quite sealed and closed. Notice the space at the top of the tube. What is this space ? It is simply a vacuum. What does that mean 1 The space is quite empty ; there is no air in it. L THE TUBE What is it that does the actual work of measuring the heat] The expansion and contraction, and consequent rise and fall of the mercury in the tube. If this measurement is to be correct, the rise and fall must be equal in all parts of the tube. Show that this could not be if the tube were, even in the slightest degree, wider at one part than another. The greatest care therefore has to be used in making these capillary tubes. They must be of uniform bore throughout. When the tubes are made, they are tested by introducing a small quantity of mercury. The mercury is moved about into different parts of the tube, and if it always measures equal lengths, the tube is proved to be of uniform bore. When a suitable tube has been obtained, a reservoir is blown at one end, and it is now ready to be filled with mercury. II. FILLING THE TUBE Show a piece of capillary glass tubing. Try and pour a little mercury into the open end of the tube. This is not possible, because of the fineness of the bore. The tube cannot be filled with mercury by pouring it in. It is a much more difficult process. Sketch on the black-board and explain. VOL. II N 178 OBJECT LESSONS STAND, iv 1. The upper end of the glass tube is heated until it becomes soft and plastic. It is then blown out into a sort of long, pointed funnel, and a little hole is made in the point. The bulb at the other end of the tube is then heated over the spirit-lamp. This heating causes the air in the bulb and tube to expand, and part of it passes away out of the hole at the pointed end. The point is immediately plunged into a vessel of mercury. As the tube cools the air left in it contracts, and requires less room. The pressure of the air on the surface of the mercury then forces some of it into the tube. 2. The tube is then placed in an inclined position in a charcoal furnace, and the bulb at its lower end is heated. The heating expands the air in the bulb and tube, and some of the expanded air escapes by the funnel at the top. It is then set upright to cool. The little air left contracts as it cools, and the mercury passes down- wards into the bulb. The same process is repeated again and again, till the bulb and part of the tube are filled with mercury. 3. The rest is easy. The mercury in the bulb is heated until it boils and begins to pass off in vapour. The vapour in escaping carries off with it all moisture and air that may still remain in the tube, and the moment the boiling mercury reaches the top, the glass tube is again softened with heat and then pinched together and securely closed. The funnel top is then removed, and the filling process is complete. When the thermometer has cooled, the mercury will be seen to fill the reservoir and part of the tube. LES. xx THERMOMETERS 179 Lesson XX THERMOMETERS I. How THE THERMOMETER is GRADUATED BY way of introduction, lead the children to tell the uses of the thermometer, and to describe the various steps in making, filling, and sealing the tube. Let us see what we have got now. We have an instrument which will tell us that one body is hotter than another. But we want something more than this. We want to be able to say how much hotter it is. We want to show the steps or degrees of heat. 1. Plunge the bulb or reservoir into a vessel of melting ice. The mercury contracts and sinks in the tube to a certain point, but it will not sink lower. We mark this point in some way on the tube, and remember it shows the melting 1 point of ice, or, as we more frequently call it, the freezing point of water. Both mean the same thing. 2. Next suspend the instrument in a vessel in which water is being boiled, so that it is surrounded on all sides by the steam of the boiling water. The mercury will expand with the heat, and rise in the tube to a certain point, but will not rise higher. We mark that point and call it the boiling point of water. We have not yet got our steps or degrees. We have found two important points one, that at which water freezes ; and the other, that at which water boils. Between these points we may make our own steps. Show a stick or piece of string, or draw a line on the black- board. Each of these measures a certain length. I could divide them into any number of equal parts. Just in the same way the space between th# freezing and boiling points of water may be divided into any number of equal parts or steps. These steps we call degrees or grades. 180 OBJECT LESSONS STAND, iv II. DEGREES AND GRADES The thermometer takes different names, according to the way in which the space between these two points is divided. 1. Centigrade. In one thermometer the space is divided into 100 equal steps, so that the freezing point is marked 0, and the boiling point 100. This is a very simple arrangement, and the instrument is known as the centigrade thermometer from centum = a hundred, gradus = a, step. It has 100 steps or grades. 2. Fahrenheit. The one most commonly used in this country places the freezing point at 32, and the boiling point at 212; thus making 180 steps between them. We call the steps in this thermometer degrees, and write them thus, 32, 212. This instrument takes its name from the man Fahrenheit who invented it. Tell that the freezing point of water is not the lowest temperature that can be reached. Fahrenheit found, by making a mixture of snow and salt, a temperature 32 lower than this, and then he thought he had actually reached the extreme limit. He called this point or zero, and worked upwards from it. Lower temperatures, however, than this have been found, since his time, and they are marked - 1, - 2 (i.e. 1 or 2 below zero). Ten degrees below zero on the Fahrenheit thermometer therefore means 32 + 10 = 42 below freezing point. In the centigrade thermometer 10 grades below zero signifies 10 grades below the actual freezing point, because the freezing point in that instrument is zero. LEB. XXI ICE 181 Lesson XXI ICE I. How WATER ACTS WHEN FREEZING LET us return to our flask and tube filled with water. A very small phial and hair-tube will be best for this purpose. We may call it our water-thermometer. (Coloured water should be used.) We will raise the temperature of the water to about 60 or 70. Test it with an actual thermometer, and let the class see it registers that degree of heat. Now we have been taught that bodies expand with heat, and contract when the heat is taken away. We should expect to find that in all bodies there would be a regular step-by-step expansion with every degree of heat added, and a corresponding regular step-by-step con- traction with every degree of heat taken away. If we raised the present temperature of the water in our phial by degrees, we should find this to be actually the case. There would be a gradual expansion with every degree of added heat. But we are not going to increase the temperature. We will lower it. Place the phial in a vessel of water of the same temperature. Stand the thermometer also in the water, so that the temperature may be shown. Now cool gradually by adding cold water. As the water in the phial feels the diminution of heat, it will gradually and regularly contract, and the column in the tube will fall. This will go on till 39 or 40 is reached. From this point, as the cooling process goes on, tlie coloured water in the tube will rise. 182 OBJECT LESSONS STAND. IT It is actually expanding again. Put some pieces of ice in the water to cool it still more, and the expansion in the tube will be seen to continue. Put in more ice, and wait till tJw thermometer marks 32. The expansion of the coloured water will still go on, for it may be seen to rise in the tube. When at last it reaches the same temperature as the surrounding water, remove the phial, and place it in a mixture of ice and salt to freeze it. The phial will in all probability burst with the experiment. This gives us another reason why water would be unsuitable fur making thermometers. II. NATURAL RESULTS OF THIS PECULIARITY IN WATER Lead the children to tell that as bodies contract their molecules are drawn more closely together. They become denser and of course heavier. When they expand, the opposite happens their mole- cules are driven apart; they are less dense, and conse- quently lighter than they were. Water contracts as it cools, till it reaches 40, but lower than that it expands. Water, then, is heaviest when it stands at 40. Imagine a pond of water in winter. The surface-water cools first, and when it has cooled to about 40 it has so far contracted that its particles are densely packed and it is heavier than the rest of the water in the pond. What must happen then ? This heavy water must sink to the bottom. It does sink, and drives up to the surface that which is not so dense and heavy. This becomes cooled and sinks in turn. So that the whole body of water is cooled. But suppose the same thing went on until the freezing point was reached. The coldest and heaviest water would be at the bottom and the ice would be formed from below upward, till the whole pond became one solid mass, killing all plant and animal life in it. LES. xxn THE WOODY STEMS OF PLANTS 183 Instead of this, the water cooling from 40 to 32 gradually expands, so that when the actual freezing takes place the mass of ice is much lighter than the water, and floats on its surface, where it forms a protecting coat for the unfrozen water beneath it. LESSONS FEOM BOTANY Lesson XXII THE WOODY STEMS OF PLANTS I. EXOGENS LEAD the children to think about the lesson on "Seeds and Seedlings" in the last year's course. How did the seeds we examined differ from each other ] Some had two " seed-leaves," some had only one. What other name can you remember for " seed-leaf " ? Cotyledon. How do we name the two kinds of seeds? Dicotyledons, monocotyledons. Have these carefully explained. How could you tell a monocotyledonous from a dicotyledonous plant 1 The leaves of the monocotyledon have parallel veins ; those of the dicotyledon have a net- work of veins. We are now going to compare these two kinds of plants in another way. Show a piece of the stem or branch of one of our timber-trees oak mil perhaps be best. Call attention to the outer covering of lark. Notice next the central pith, with the hard solid wood arranged round it, layer after layer, in concentric circles. When the tree was young, this pith was a very thick 184 OBJECT LESSONS STAND, iv cord of soft, greenish, pulpy matter, and took up nearly all the centre of the stem and branches. It was through this central pith that the dissolved earth-food absorbed by the roots rose upwards to the leaves. It had then only one woody layer round it. Next year, however, and each year after, a new layer of wood was formed on the outside ; and these rings of new wood, growing one by one, compressed the pith, till at last it became a mere thread. We can see in our piece of oak only the spot where it once was in the centre of woody rings. Lead the class next to tell that ihe oak grew from an acorn, and that the acorn is a dicotyledon. As the stems of all dicotyledons grow like the oak by the yearly addition of a woody layer on the outside, we often speak of these plants as " exogens." The word "exogen" means "growing outwards." Explain that the great majority of all the plants in every part of the world are exogens, and of course dicotyledons. Lead the class now to enumerate the distinctive marks of the dicotyledons. 1. The seeds have always two seed-leaves. 2. The stem has a central pith, round which the wood forms year by year in concentric layers. 3. The oldest, densest, and hardest wood is in the centre. 4. The stem is clothed with a more or less rough outer bark which may be peeled off. 5. The leaves always have their veins arranged in a network. II. ENDOGENS Show next a piece of cane or bamboo. A piece of sugar- cane would serve the purpose admirably. Notice the entire absence of any outer cork-like bark. Cut through the stem, and show that there is no central pith, and that the wood does not grow in concentric layers or rings. LES. xxii THE WOODY STEMS OF PLANTS 185 Split the stem lengthwise, and point out that the wood is arranged in threads or fibres. Tear away some of these woody fibres, and show how they extend parallel or side by side through the stem from root to summit. There is a pith, but it is mixed up with the parallel threads of wood. It occupies the spaces between the threads, or in other words the parallel bundles of woody threads pass upwards through the pith. Set one of the children to cut through the cane. Lead him to tell that he finds the outside very hard indeed. Let him now press the point of the knife into the central part of the cane. He finds the inner wood much softer than that on the outside. Explain that in plants of this kind the new wood is formed in bundles of parallel threads or fibres, through the centre of the stem. That is to say, they increase or grow " from within." We describe such plants as endogens. The word "endogen" means "growing from within." Lead the class to see that as the new wood is always deposited in the centre of the stem, that which has been already formed is continually being forced outwards. In this way the outer fibres become compressed and very dense. This explains why the outside of the cane is so hard to cut, while the central part is soft. The cane and the bamboo are monocotyledonous plants. In every monocotyledonous plant the woody stem grows always from within. They are all endogens. The monocotyledons or endogens form a small class of plants. The palms, canes, and bamboos are the chief among those with woody stems. Let tJie class now tell the distinctive marks of the mono- cotyledons. 1. The seeds have a single seed-leaf. 2. The stern grows from within by the addition of bundles of parallel woody fibres through its centre. 3. The oldest and hardest wood is on the outside. 4. There is no bark. 186 OBJECT LESSONS STAND, iv 5. The leaves have their veins arranged as nearly as possible parallel to each other from foot-stalk to tip. Lesson XXIII THE WOOD OF THE EXOGENOUS STEM SHOW the piece of oak-stem again. Let the class tell all they know of its structure the concentric layers of wood, with the spot showing the original position of the pith. What is the meaning of these woody layers ? What was the purpose of the pith before it became dry, dead, and useless 1 Notice too the bark. What lies immediately under the bark in all such stems 1 The last-formed layer of wood. I. THE MEDULLARY RAYS Continue the examination of the oak-stem. Call attention to the silvery white streaks running irregularly from tJie central pith to the bark which surrounds the stem. They appear to be mere lines radiating like the spokes of a wheel from the centre of the stem. We speak of them as the medullary rays. Explain that if the stem were cut lengthwise, we should find tliat tliese " rays " are not lines that each of them is, in fact, a thin wall which radiates from the centre to the outside of the stem. When the stem is cut across as this one is, only the edges of these radiating walls are seen, and they appear to be mere lines. Tliese thin radiating walls consist of the same soft cell-tissue as the pith an entirely different substance from the hard, fibrous, woody tissue of the wedge-like blocks between them. LES. xxni THE WOOD OF THE EXOGENOUS STEM 187 This is why the name medullary is given them. Explain carefully the meaning of this term. What is the work of the pith in the growing plant ? Tell that this cell-tissue of the medullary rays is for the same purpose. It forms channels for the passage of the sap upwards, and between the pith and the bark. Explain that the cabinetmaker depends very largely on these medullary rays for the beauty of his polished woods. He calls them the silver grain of the wood. The beauty of the various ornamental woods used by the cabinetmaker depends upon the closeness of their texture, and the skill in cutting so as to expose this silver grain. II. HEART- WOOD AND SAP-WOOD Examine once more the piece of oak-stem. Which part of this wood was first formed, and is there- fore the oldest ? The central part of the stem. What happens to this central part as outer layers are formed one by one round it 1 The outer layers press upon it more and more, and it becomes denser and denser. Let one of the class try to force the point of a knife into this centre of the stem. He find>s it very hard indeed. He cannot force the knife in. Tell that this is commonly known as the heart-wood. // is the hardest wood in the tree. Heart of oak is always selected for purposes where strength and durability are required. Tell of our old ships of war, that were always built of this wood. Show now a branch of some growing tree. Strip tJie bark from it. In the spring and early summer we should always find between the bark and the wood a Sticky, watery fluid. This is the sap which has found its way upwards through the medullary rays and is being deposited here. From this fluid a new layer of woody matter is formed during the growing season. It is, at first, soft 188 OBJECT LESSONS STAND, iv and somewhat pulpy, but in time hardens into actual wood. We call this the sap-wood. It is of course the newest formed wood in the tree. Explain that while this liardening process is going on, the sap-wood continues to afford a channel for the upward passage of the sap. Remind the class that in the young plant this work is done by the pith. But as the tree grows, both the pith and the heart-wood round it cease to take any active part in the life-work that is going on in the tree. This has to be done by the younger sap-wood and the medullary rays. The heart -wood becomes darker and more deeply coloured than the layers around it, and it is this gradua- tion of colouring that makes our cabinet- woods so beautiful. III. HARD WOOD AND SOFT WOOD The usefulness of a piece of timber depends upon two things : the age of the tree, and the part of the tree from which it is taken. Tell that trees, like animals, grow till they reach maturity, but after that they begin to decay. The age for reaching maturity depends on the nature of the tree, as well as on the soil and climate. The tree which is felled at its maturity yields the best timber. At this period the whole of the trunk, except of course the new sap-wood, is equally good. In a young tree the heart-wood is always the best ; but after the tree has passed maturity, this heart-wood is the first to decay. In the young tree, on the other hand, the sap-wood is always the worst part of the timber, and is liable to decay quickly. But after the tree has readied its maturity, even the sap-wood becomes good, useful timber. LES. xxiv THE OAK AND THE FIR 189 Lesson XXIV THE OAK AND THE FIE (A COMPARISON) IN our last lesson we took the oak as the representative of dicotyledonous or exogenous trees. Let the class explain the meaning of these terms, and show their application to this large family of plants. There is a large and valuable family of timber- trees the firs and pines which are usually classed with the dicotyledons, but they differ from the oak and other timber- trees in many important particulars. Among the firs and pines we include the Scotch fir, the spruce fir, the silver fir, the cedar, the yew, and the larch, and the pines of Sweden, Norway, Eussia, Germany, and Canada. Let us see how these trees differ from the oak and the other exogens. I. THE FRUIT AND SEEDS Show a few acorns, and let the children tell that these are the fruit of the oak. They belong to the class of fruits commonly known as nuts. The seed-vessel itself develops into a hard shell which holds and protects the single seed. Among other fruits of a similar kind are the hazel- nuts, filberts, beech-nuts, and chestnuts. Remove the seed itself from the shell, and let the children examine it and give their reasons for calling it a dicotyledon. Next show a pine-cone. Tell that this is the fruit of the fir and pine family of trees. Have it examined by the class. Notice that it consists of a great number of dry, hard, thick scales. This cone is really a great many fruits in one for each of these scales is a single fruit. 190 OBJECT LESSONS STAND, iv Lead the class to tell that, in all plants, the fruit is simply tlie ripened pistil of the flowers. Explain that in the case of the pines and firs the pistil of each flower, instead of being folded up to form a sort of Iwllow receptacle for the seed, is simply a flat open leaf, joined, like the rest, to a common central stalk. As the cone ripens, these individual leaves become dry, hard scales such as we see in the pine-cone. In these scale-like pistils, too, the seed is not enclosed in a seed-case as we find in most plants. It is simply attached to the upper surface of the pistil-leaf, near the central stalk. When the cone is quite ripened, the scales curl up, and the seeds themselves fall to the earth. Explain that the fir and pine family are often described as the cone-bearing trees, because they are the only trees which bear fruit of this kind. II. THE STEM SIww pieces of oak and fir stems. Let the children take tJiem and examine them for themselves. What difference can you see in the two 1 Lead them to tell that in each there is the same outer bark, the same central pith-spot, with the same ring-layers round it, telling of as many yearly additions in the growth of the tree. There is no difference in the appearance of these stems. Explain that pines and firs differ from the oak family in one very important particular. Their stems yield the inflammable substances known as turpentine and resin. They are described as resinous trees. To obtain the resin the stems of the trees are pierced with holes, and from the holes these resinous substances exude in the form of a liquid, not unlike honey in appearance. This thick, honey-like liquid is put through various pro- cesses, and is made to yield the solid resin and the thin, clear, liquid oil of turpentine. LES. XXIV THE OAK AND THE FIR 191 We shall deal further with these substances in a later lesson. N.B. There is no such resinous substance from the oak. III. THE LEAVES Show, if possible, some oak-leaves. Let the children examine them and tell their characteristics. They are net- veined leaves, and consist of a blade and a foot-Stalk, as is usual with the leaves of all dicotyledonous plants. The microscope would show us the stomata or breathing pores studded all over the blade. Now show some pine-leaves. Let the class compare them with the leaves of the oak. Notice that tliey are mere spikes or needles. They are known as needle-shaped leaves. Tliey are found only on trees belonging to this group. They grow in clusters of from two to five, and have small scales at their base. As a family these trees are all evergreens ; that is to say, the new leaves always make their appearance before the old ones fall off, and hence the trees are always green. The larch, however, sheds its leaves as winter ap- proaches. Is the oak an evergreen 1 It would be well to tabulate on the black-board the distinctive characteristics of these two families of trees. THE OAK 1. The oak is an exogen. 2. The fruit of the oak is a nut. 3. The acorn the seed of the oak is enclosed in a shell. 4. The oak has no exudation. 5. The leaf of the oak is a blade with a network of veins and stomata. 6. The oak sheds its leaves before winter approaches. . THE FIR 1. The fir is an exogen. 2. The fruit of the fir is a cone. 3. The fir-cone bears naked seeds on its upper surface. 4. The fir is a resinous tree. It yields turpentine and resin. 5. The fir bears clusters of needle- shaped leaves, with no net- work of veins. 6. The fir family are evergreens. 192 OBJECT LESSONS STAND, iv Lesson XXV TIMBER I. HARD AND SOFT WOODS PLACE a piece of ebony or lignum vitae in a basin of water and it mil sink. Next try pieces of oak and Spanish mahogany. Tliey float with the upper edge almost on a level with the surface of the water. A piece of yellow pine floats higher out of the water ; larch higher than the yellow pine; and common poplar higher still. Why does the ebony sink ? Because it is heavier than the water. Remind the class that heavier means denser. The molecules of the wood are packed very closely ; there is much matter in them. The piece of poplar floats high out of the water. Why ? Because it is lighter than the water. What does that mean? It means that the molecules of this wood are less densely packed ; the substance of the wood is loose as compared with the ebony. The oak, mahogany, yellow pine, and larch are examples of the varying degrees of density between the ebony and poplar. Why are some bodies denser and heavier than others ? Because the force of cohesion binds their molecules more closely together. Lead the class to tell tliat the stronger the forces of cohesion, the greater will be, not only the density and weight, but also the hardness of the body. This is a general rule. We are able to judge as to the hardness of different woods by their action in water. Hence ebony and lignum vitae represent very hard LES. xxv TIMBER 193 woods ; poplar a very soft wood. The rest show varying steps between these two extremes. II. SEASONING OF WOOD Newly -felled timber is unfit for use. It is not only weak, but is liable to warp, twist, and change its form. In this state it is known as green wood. The outer surfaces, acted upon by the air, crack and split more than the inside. All timber requires to be well seasoned to make it durable. It must be cut up by the saw while green, and exposed to the air for a long time. The result of such exposure is to gradually dry the whole of the wood. The surrounding air first absorbs all moisture from the surface, and then as the outside dries, the air by degrees finds its way to the inside, and the whole becomes uniformly dry. With some woods this seasoning or drying is done in an artificial way. The wood is placed in a drying-room, and a current of air at about 90 or 100 is passed over it. This hot, dry air soon absorbs all the moisture from the wood, and seasons it as effectually as years of exposure would have done. III. SHRINKAGE OF WOOD During the seasoning process the wood shrinks, but always according to a natural law. That is to say, the amount of shrinkage in length is so small that it may be altogether disregarded. It is in the breadth of the plank that the shrinkage takes place. Lead the class to think again of the structure of the exogenous stem. Let them tell that the woody fibres are arranged lengthwise down the stem in irregular circles, and that these fibres are bound together by the radiating plates, known as the "medullary rays "or the " silver grain." Impress upon them the fact that this "silver grain" is not of VOL. II 194 OBJECT LESSONS STAND, iv the same nature as the woody fibres ; it resembles the pith in structure. As the drying process of the seasoning goes on, the woody fibres contract or shrink in bulk. But they can only shrink in this way by, at the same time, tearing the medullary rays. That is to say, the shrinking of the woody bundles finds relief by splitting the timber in the direction of the medullary rays. This explains why timber, after it is cut, and before it is properly seasoned, always cracks and splits on the outside more than the inside of the mass. It would be interesting to note the behaviour of a trunk of one of the stronger exogenous woods, such as oak or beech, if cut up info planks. Imagine a trunk cut lengthwise by the saw into seven planks. After the planks had been properly seasoned, the middle one would be found to retain its original thickness in the centre, but the edges of the board would be thinner. The breadth of the plank would be the same as at first. The medullary rays being closer together towards the centre of the trunk, offer greater resistance there to the tearing than at the edges. The planks on either side of the middle one would, from the same cause, become bent out of shape, or pulled round into a convex from the centre of the trunk, and each board would be narrower. IV. PRESERVATION OF WOOD Timber is liable to decay from many causes. Among these, moisture and changes in temperature are its worst enemies. They not only lead to decay of the wood, but they encourage the attacks of insects and worms, and the whole substance of the wood gradually crumbles away. Where timber structures have to be exposed to all the changes of air, light, heat, and moisture, something must be done to protect them from the effects of these. LES. xxvi TIMBER ITS USES 195 Lead the class to tell why we use paint, coal-tar, and other substances for covering woodwork ; why, in fixing a wooden post in the ground, we always soak the lower end in tar, or stand it in pitch; why ships, boats, and barges are always kept well painted and tarred. Another enemy to timber is dry-rot. The simplest and best way of preventing this is to saturate the wood in oil. Lesson XXVI TIMBER ITS USES I. TIMBER AND WOOD THE trunks of all our trees yield wood. The only distinc- tion between timber and wood is that the timber -trees are so large that their trunks may be sawn up into pieces not only long, but wide and thick as well. Such pieces of wood we call logs or balks of timber. They may be used in that state, or they may be sawn up into planks. In any case, by the term timber we mean great balks or planks of wood which, from their size and quality, are fit to be used in engineering and building. For all such purposes, strength and durability are, of course, the primary objects. Amongst the chief of these timber -trees are the ash, beech, cedar, elm, fir, hornbeam, larch, lime, mahogany, oak, poplar, teak, etc. The various ornamental woods used by the cabinetmaker form a class by themselves, and are not included under the head of timber. Among these are the ash, birch, box, cherry, ebony, maple, rose-wood, satin-wood, walnut, etc. II. USES It is the special quality of each individual wood that renders it specially fitted for some particular kind of work. The woods may be classified in some such way as this : 196 OBJECT LESSONS STAND, iv 1. Durable for dry carpentry. The cedar, yellow deal, and poplar. 2. Durable for wet carpentry. The alder, white cedar, and plane. 3. Elastic woods. The ash, hazel, hickory, and yew. 4. Even grain. The beech, lime, pear, and pine. 5. For ship-building purposes. The oak, teak, fir, and larch. 6. For machinery. Box, beech, hornbeam, mahogany. 7. For turnery. The alder, apple, birch, holly, plum, sycamore, and willow. 8. For furniture. Amboyna, beech, cherry, ebony, maple, mahogany, oak, rose-wood, satin-wood, walnut, etc. Show as many specimens of these woods as can be obtained, and lead the class to tell as far as they can where we may meet with articles made from them. III. SOME OF OUR PRINCIPAL TIMBER-TREES 1. The Ash. Show a picture of the tree, and a specimen of the wood. This wood is specially valuable for its great toughness and elasticity. It is coarse in texture and of con- siderable strength. It is much used in building and engineering. It is the principal wood of the wheel-wriglit, on account of its elasticity. He makes the spokes of the wheels and the shafts of carriages of this wood. For the same reason it is specially fitted for all purposes where severe shocks and wrenches have to be provided against. This explains why it is the best wood for making hammer- shafts and the handles of tools generally. 2. The Beech. Show a picture of the tree and a specimen of the wood. This wood is almost as strong as oak, but it is specially distinguished for its closeness of grain, and the even smoothness of its surface. It polishes readily, and is a LES. xxvi TIMBER ITS USES 197 beautiful wood, when it is so cut as to skilfully expose the silver grain. It is much used for furniture ; and is also largely employed, because of its closeness, toughness, and strength, for making cogs for mill-wheels. 3. The Elm. Show, as before, a picture of the tree, and a specimen of the wood. It is a rough, cross-grained wood, of considerable strength. It is very durable under water; but it rapidly decays if it is subjected to frequent changes from wet to dry. Hence it is not a good wood for exposure to the atmosphere in a climate such as ours. It is chiefly used for rough purposes, where toughness and strength are required. The wheel-wright makes the nave of his wheel of elm, and this wood is also used for making pulley-blocks. 4. The Fir. The fir and pine family are perhaps the most valuable of all our timber-trees, because they are plentiful and therefore cheap. The wood of these trees is not so strong nor so durable as many other kinds of timber ; but it is easily worked. The family comprise a great variety of trees. The most durable among them are the larch, the pitch-pine, and the firs of Norway, Sweden, Eussia, and Germany. These trees yield resin, turpentine, and pitch. The white and yellow pine of the Canadian forests is not one of the strong durable woods ; but it is much in demand in this country, because it is so easily worked. The Scotch fir yields a very valuable timber, little inferior to oak. It is obtained from Scotland, Sweden, Norway, and Russia, and is frequently named red pine, red deal, and Riga fir. The spruce and silver firs are employed largely for making ladders, masts of ships, scaffolding, etc. Show specimens of these woods. 5. Hornbeam. Show a picture of the tree and a specimen of the wood. 198 OBJECT LESSONS STAND, iv This, from the closeness of its grain and the remark- able toughness of its fibres, is largely used by engineers for the teeth of COg-wheels. It is also used for making mallet-heads. 6. Mahogany. Show a picture of the tree. Describe the tree of Honduras (commonly known as the Spanish mahogany). In comparison with this giant all other trees look insignificant. It is sometimes called the "king of the forest trees." Show a specimen of the wood. Call attention to its beautiful close-grained texture. It is highly valued for furniture -making, but will not stand exposure to the weather. The wood of the limbs or branches is preferred for ornamental purposes, because the grain is closer, richer, and more variegated than in the trunk itself. 7. Oak. Show a picture of the British oak and a specimen of the wood. This is one of the strongest and most durable of woods. It suffers less than any other from water or changes in climate. It stands first among the hard- wooded timber-trees. It is highly prized for ship- building purposes. It is also invaluable for making roofs ; for which purpose its lightness combined with its strength and durability specially fit it. 8. Teak. Show a specimen of this wood. Of all the hard woods imported into this country, teak is the most valuable. It is useful for all purposes in which we employ oak. It is equally durable, and is not subject to decay through exposure to a hot climate, nor from worms or insects. It is very stiff and tough. It is used largely in ship-building, and in making gun-carriages. LES. xxvn THE ATMOSPHERE WHAT IT IS 199 BOYS OE GIELS Lesson XXVII THE ATMOSPHEEE WHAT IT IS WE have learned a great many facts about the atmosphere as a material substance about its weight and its pressure in all directions, and how it affects other bodies. We have now to study it from another point of view. I. NITROGEN Take a large glass pickle-jar, and either cut or crack off the bottom. Cork the neck carefully, and thus extemporise a kind of bell. Of course a proper bell-jar would be preferable if it could be obtained, but this will serve the purpose. The bell contains nothing but air. Place a piece of phosphorus about the size of a pea on a little tin plate, and let the plate float in a large basin of water. Now light the phosphorus with a taper, and cover it quickly with the beli-jar. The phosphorus burns with an intensely bright flame in the jar, and gives off dense white fumes. Wait till the fumes clear off, and then show that the jar, which was at first full of air, now contains a great quantity of water. Actual measurement would prove that the water occupies about one-fifth of the jar. Now we know that the water and the air could not occupy the same space one must make room for the other. It is the air in this case that has made room for the water, for there is now only about four-fifths of the original quantity in the bottle. Our next business will be to see whether what is left in the jar now is the same as it was before the experiment. 200 OBJECT LESSONS STAND, iv Light a taper or a splinter of wood and show that it burns in the air. Now plunge it into the neck of tJie jar. It is immediately extinguished. Lower a piece of burning phosphorus into it. The result is the same. It goes out. The gas, therefore, which is now in the jar is not air as it was at first. One-fifth of its bulk has been burned away, and the remaining four-fifths is a gas which puts out a flame. It will not allow anything to burn in it. Tell that the name for this gas is nitrogen ; and that it forms four-fifths of all the air around us. II. OXYGEN Prepare three or four bottles of oxygen by heating in a retort some chlorate of potassium mixed with about one-sixth its weight of black oxide of manganese. Colled the gas in bottles by displacement of water in the usual way. Hold up the bottles. There is nothing to see. The bottles appear empty. Show another bottle, empty in the ordinary sense of the word. The children know that it is not really empty. It is full of air. Neither are these other bottles empty, as we shall see, although they do not contain air. 1. Light a splinter of wood. It burns in the air. Blow out the flame, leaving only a red spark, and plunge it into one of the bottles of this strange gas. The spark at once bursts into flame again and burns with a very brilliant glow. It burns more brightly and more fiercely than it did in the air. 2. Repeat the experiment in the other bottles with a piece of red-hot charcoal, a bit of burning sulphur, and a piece of phosphorus. All these things burn in the air, but they burn much more fiercely and brilliantly in this gas. Tell that the name of this gas is oxygen. It is a powerful supporter of combustion or burning. It was this gas which disappeared in the bell-jar. The burning phosphorus went out immediately it was all gone. LES. xxviii MORE ABOUT THE ATMOSPHERE 201 We afterwards found out that the other gas, nitrogen, that was left behind, would not support burning, but ex- tinguished the flame at once. Oxygen formed one-fifth of the bulk of the air in the bell-jar ; it forms one-fifth of the bulk of the air all over the world. But why not have an atmosphere all oxygen ? Burning would go on too fast Eemind the dass how fiercely the flame burned in the bottles of oxygen. We shall have to learn too, presently, that we and all animals live by burning. Our bodies are daily and hourly burning away. If we lived in an atmosphere of oxygen, we should burn away too fast and live too rapidly, like the flames we saw just now. An atmosphere of nitrogen only, on the other hand, would not do, for in it there could be no burning, and without burning there could be no life all animals and plants would die. Tell that the one part of oxygen is diluted by being mixed with four times its bulk of nitrogen, just as we dilute vinegar, milk, wine, brandy, and other things with water. Thus diluted it forms just the atmosphere required. Lesson XXVIII MORE ABOUT THE ATMOSPHERE I. RECAPITULATORY CAREFULLY recapitulate the subject-matter of the last lesson. Lead the children to tell the composition of pure air the proportions in which the two gases oxygen and nitrogen are mixed in the air the nature of each gas. What is the purpose of the gas nitrogen ? What would be the effect of an atmosphere of pure oxygen ? Let the class describe the various experiments shown. 202 OBJECT LESSONS STAND, iv II. WHAT ELSE ORDINARY Am CONTAINS We have just learned that air is a mixture of the two gases oxygen and nitrogen. We could make some air for ourselves by preparing one bottle of oxygen and four similar bottles of nitrogen, and mixing them together. The mixture would be pure air. But the air all round us is never a perfectly pure mixture of oxygen and nitrogen. I think you can tell me of something else it contains. 1. Carbonic acid gas. Refer to the lesson on carbonic acid gas. Lead the class to tell the sources of this gas in the air, from the burning of our fires and furnaces, and from the breathing of animals. How shall I prove that there is carbonic acid in our breath ? By breathing into lime-water. If I burn a taper in oxygen, I know that carbonic acid is produced, but how can I prove it ? By shaking up some lime-water in the bottle. Thus far we simply know the fact that the burning of the taper in oxygen produces carbonic acid gas. Let us now learn the reason why. Take the bottle in which the piece of carbon was burned, pour some clear lime-water into it, and shake it up. What do we see 1 The lime-water has become cloudy or milky-looking. What does that prove? That the bottle contained carbonic acid. We burned a piece of charcoal in this bottle, and char- coal has another name carbon. Whenever we burn carbon we produce carbonic acid. Then it is clear that the taper must contain some of this carbon, for when it burned it produced carbonic acid. Tell that not only the taper, but wood, coal, coke, fuel of every kind, as well as candles, oil, and coal-gas, all contain carbon. It is the carbon in them which makes them valuable as substances for burning; and the burning of all of them produces carbonic acid. LES. xxix WATER ITS COMPOSITION 203 Yet with all the fires and lights, and all the many millions of animals breathing out carbonic acid, there is never more than a mere trace of this gas in ordinary air usually about 4 parts in 1000. How is this? Let the class explain that plants take in this gas which animals breathe out. Every plant that grows requires carbonic acid just as we require oxygen. They take carbonic acid from the air, and so a balance is kept between the wants of animals and plants all over the world. 2. Water- vapour. Refer also to the lesson on water- vapour. There is always more or less water-vapour in the air. Make the class tell that the air is porous and absorbent, and absorbs water-vapour into its pores. The air consists of a mixture of molecules of the gases oxygen and nitrogen. These molecules have no cohesion, and the spaces between them form the pores into which the water-vapour is absorbed. Close with a few useful hints on practical ventilation. The object of ventilation is to get rid of the injurious carbonic acid gas. Ventilation should provide for a flow of good air into the room somewhere near the floor, and an outlet for the bad air, with its carbonic acid, near the ceiling. Why ? Lesson XXIX WATER ITS COMPOSITION I. HYDROGEN TAKE a flask or bottle, well corked, and furnished with a thistle tube and a piece of bent glass tubing. Put some zinc clippings into the flask, with just enough water to cover them, and then carefully pour in, through the funnel, a little sulphuric acid (oil of vitriol). The liquid mixture will at once begin to bubble and effervesce all round the pieces of zinc. These bubbles are bubbles of gas. We call this gas hydrogen. The zinc 204 OBJECT LESSONS STAND, iv is really separating this gas, hydrogen, from the dilute acid. When the hydrogen has quite filled the flask, it will begin to force its own way outwards through the tube. Dip the end of the tube into the water in the trough, and show the bubbles of gas rising upwards to the surface. Collect some of the gas in a bottle filled with water and in- verted in the trough in the usual way. There must be no air mingled with the hydrogen, or our experiment may result in an explosion. Catch a little of the gas in a small test-tube first, and apply a lighted match. The gas, if pure, will burn quietly without exploding, and may be collected in the bottle for experiment. Our bottle is now full of this new gas, hydrogen ; but before we begin to examine it, I want you to think about the other gas, oxygen, which we talked of in the last lesson. What are the two chief properties of oxygen? It makes other things burn; it does not take fire itself. Why do things burn in the air ? Because the oxygen in the air makes them burn. They burn more slowly, however, than they would in pure oxygen. When we burned carbon (charcoal) what did we get? Carbonic acid. How was this formed ? The carbon united with some of the oxygen and formed a new substance carbonic acid gas. The oxygen in combining with the carbon produced heat the more oxygen the greater the heat, and the greater the amount of carbonic acid formed. Now let us return to our new gas, hydrogen. We have here a bottle filled with the gas. What can we learn about it ? Take the bottle of hydrogen keep it mouth downwards, and plunge a lighted taper into it. Call upon the class to describe what takes place. The gas hydrogen catches fire and burns with a blue flame in the mouth of the bottle, but the flame of the taper LES. xxix WATER ITS COMPOSITION 205 itself is no longer burning. It has been extinguished by the gas. Remove the taper and show that it again takes fire as it passes through the flame of the gas at the mouth of the bottle, but that as soon as it is plunged into the bottle again it goes out. What have we learned from all this ? That hydrogen is a very different gas from oxygen. Hydrogen is very inflammable ; it burns with a blue flame. But oxygen will not take fire. Hydrogen will not allow other things to burn in it, but oxygen helps all other things to burn. It is the great agent of burning. What was it that made the hydrogen burn in the mouth of the bottle ? The oxygen in the air all round. If there had been no oxygen present, the hydrogen would not have taken fire ; for oxygen makes hydrogen burn as well as other things. II. WHEN HYDROGEN BURNS, WATER is FORMED Remove the piece of bent tubing from the flask, and in its place fix a straight tube, with the upper end drawn out to a point. See that cork and tubes fit air-tight. Now pour a little more sulphuric acid down the funnel into tJie flask, and the effer- vescence mil commence again. Hydrogen mil pass off in bubbles and Jill the flask once more. As it fills the flask, it must find some way of escape. It will escape up the straight tube. Place a small dry test-tube over the top of the tube and collect a little of the gas as it comes off. Test it by applying a lighted match to it. As soon as it is clear that nothing but hydrogen is coming off, bring a light near the top of the tube, and the gas mil burn with a pale blue flame. Cover the flame with a dry, cold glass, and after holding the glass there for a short time, call attention to its appearance. The inside of the glass soon becomes covered with little dew-like drops of moisture. 206 OBJECT LESSONS STAND, iv How did this moisture get into the glass ? Hydrogen burns and forms a new substance water ; just as carbon burns and forms a new substance carbonic acid. The new substance, carbonic acid, was made by the union or combining of carbon and oxygen when heated ; the new substance, water, has been made by the union or combining of hydrogen and oxygen when heated. Tell that the water as it is formed from this burning hydrogen is not liquid as we usually see it. It is made in the form of steam or water-gas. We could not see it until we placed the glass over the flame. Then the steam came into contact with the cold glass and condensed into little drops of actual water. So then we have seen that out of fire comes water. Strange as this may appear, it is quite true ; and more than that, we may say that out of every fire* comes water. Our fuel and candles of all kinds, the oil we burn in our lamps, the gas which lights our streets and houses, all contain hydrogen as well as carbon. What then must be formed when such things burn 1 Water. Hold the cold shovel over the fire for a minute or two. Re- move it and drops of moisture will be seen on it. This moisture came from the burning of the coal and wood, for these substances contain hydrogen, and hydrogen burns and forms water. *N.B. This would not be true of a fire made exclusively of coke. Lead the class to tell why. GENEEAL STEUCTUEE OF THE HUMAN BODY Lesson XXX THE BONY SKELETON Snow a good wall-sheet picture of the full-sized skeleton of a man. This represents the strong framework of hard firm LES. xxx THE BONY SKELETON 207 bones on which our bodies are built up. We call it the skeleton ; and it consists of upwards of 200 distinct and separate bones of various shapes and sizes. The skeleton determines the shape of the body. Show pictures of other skeletons say those of a horse, a rabbit, a bird. In each case the skeleton itself suggests the well-known shape of the individual body. The skeleton gives Strength and Solidity to support the softer fleshy parts. Call attention to the strong pillar-like bones of the legs which support the body upright on the feet ; then tell of the strong backbone which continues this support upwards. Point them out on the diagram. The body consists of three parts head, trunk, and limbs. I. BONES or THE HEAD The head is made up of two parts the skull and the face. 1. The skull is a hollow box intended to hold and protect the brain. It is built of eight separate bones most of them broad flat plates. They are joined together firmly at their edges, because, as they simply form a box, there is no need for these bones to move. 2. The face comprises all the rest of the head that is not included in the skull. It is formed of no less than fourteen separate bones. It will not be advisable in these lessons to insist on the naming of all the bones in the skeleton. The general arrange- ment and the special adaptability of the most important mil be all that is necessary. Thus tell of the orbits or sockets in which the eyes are lodged, and the providential means taken to protect those precious organs from injury. They are surrounded by the broad frontal bone of the forehead above, the nasal or nose-bone, and the two malar or cheek-bones below. These effectually protect the eyes from injury. 208 OBJECT LESSONS STAND, iv Only one of all these fourteen bones is capable of move- ment. Which is it? The lower jaw-bone. Why should this move ? All the other bones are firmly fixed to each other. This bone is attached on either side by a sort of hinge to the other bones of the skull, and can be pulled up and down, so as to open and close the mouth. Both jaws are armed with teeth for biting and chewing our food. We have, during our lives, two sets of teeth ; the first, called the milk teeth, which are twenty in number, and fall out while we are young; the others, known as the permanent teeth, because they last througli the rest of our life. The permanent teeth are larger and stronger than those of the first set, and there are thirty- two of them instead of twenty. II. BONES OF THE TRUNK The trunk is that part of the body which would be left if the head and limbs were lopped off. The main pillar which supports the body is the back- bone, which extends from the neck to the bottom of the trunk. The name backbone is a little misleading. It is not one long bone, but a string of many bones. Each of these bones is called a vertebra, and the proper name for the whole string of bones is the vertebral column. The vertebrae are joined together by thick smooth pads of gristle, which form springy, yielding cushions between each bone and the one above it. Why should such an arrangement be necessary ? Picture a man with a bone rigid as a poker down his back ; and then refer to the feats of acrobats, tumblers, and rope-walkers. It is the jointed backbone with the pads of gristle which give this freedom of movement. The seven smallest and topmost vertebras form the bones of the neck ; they support the head. LES. xxx THE BONY SKELETON 209 The next twelve vertebrae below these support the twelve pairs of ribs, one rib on each side. Below these are the five lumbar vertebrae (vertebrae of the loins). Notice that the bones have been increasing in size and solidity downwards. The remaining bones which form the base of the column are very thick, solid, and strong. The vertebral column of a child contains 33 distinct bones. As the child advances into adult life the five vertebrae next below the lumbar vertebrae grow together, and become welded into one piece, which is known as the sacrum ; at the same time the four lower- most bones also grow together and form one piece a sort of rudimentary tail. Hence the total number of vertebrae in the adult is only 26. The haunch or hip bones can be felt at the hips. They are very peculiar in shape. Point them out on the diagram. They meet in front and form a sort of bony basin the pelvis. Point out the ribs on the diagram. They form a kind of hollow bony cage in the skeleton itself. This we call the chest. The ribs strengthen and protect this chamber. Compare the hoops round a cask. Point out that most of them are joined in front to another bone the breastbone. Tell that the ribs are not fixed immovably to the vertebrae. They are able to move up and down. Show that they do not pass horizontally round the body, but slant downwards. When they are moved upwards, therefore, they make the inner chamber larger ; when they are depressed it becomes smaller. III. BONES OF THE LIMBS The arms are joined to the trunk by two bones the blade-bone behind, and the collar-bone in front. These form the shoulders. VOL. II P 210 OBJECT LESSONS STAND, iv The legs are joined to the trunk by means of the hip- bones. The arm consists of three parts the upper arm, the fore-arm, and the hand, and has thirty-two distinct bones. The leg corresponds to it, and consists of an upper leg (thigh), a lower leg, and a foot ; but it has only thirty separate bones. Why these distinct parts and this large number of separate bones in each limb ? The upper arm and the thigh each consists of one single bone. The bone of the upper arm is joined to the shoulder- blade ; the bone of the thigh to the hip-bone. The fore-arm consists of two bones (one larger than the other) jointed at the elbow to the bone of the upper arm. The lower leg also consists of two bones (one larger than the other) jointed at the knee to the thigh-bone. The knee differs from the elbow-joint in having a small flat bone the knee-cap placed over the joint. There is no such bone in the arm. The hand and foot are built on very much the same plan. The wrist of the one corresponds to the ankle of the other. The wrist has eight little bones ; the ankle seven. The palm of the hand corresponds to the sole of the foot, and each of them has five bones running through it, connecting the wrist and the ankle with the fingers and the toes respectively. The hand has four fingers and a thumb each finger being formed of three bones; the thumb of two. The foot in its turn has four toes and a great toe ; the great toe having two bones, the others three each. Compare the bones of the hand and foot, and show their peculiar adaptability in each case. In the hand, the wrist-bones are small, and the bones of the fingers very long. The corresponding bones in the foot are short, thick, heavy, and clumsy in appearance. The thumb too is placed so as to move in the opposite LES. xxxi THE JOINTS 211 direction to the fingers ; the great toe has little or no movement. Lead the children to tell that in the one case strength and solidity of support is all that is needed ; in the other flexibility and rapid movement, delicate touch, and firm grasping powers have to be secured. Lesson XXXI THE JOINTS I. INTRODUCTION LEAD the children to tell that the bony framework or skeleton of the body consists of more than 200 distinct bones, and that the object of this large number of pieces in the human machine is to secure easy and free movement wherever movement is necessary. Some of the bones, e.g. those of the skull and the face, are not meant for movement. Such bones are united firmly and immovably together. Let us look at some of the bones that do move ; and try and find out how they are attached to each other. Bring a child to the front and put him through a few move- ments such as opening and closing the hand, drawing up the elbow and knee, swinging the arms round in a circle, and turning the head to the right and left. Explain and show that each of these movements is different from the others. Tell that such a variety of movement must be brought about by a similar variety of arrangement in the bones themselves, and the way in which they are connected with each other. II. JOINTS When two bones are connected in such a way that we can bring them together or straighten them out, as the boy did just now with his hand, arm, and leg ; or swing one round the other as he swung his arm round at the shoulder, they form a joint. There are many joints in 212 OBJECT LESSONS STAND, iv the body, and they differ among themselves in their form and mode of action. We generally arrange them in three classes hinge-joints, ball-and-socket joints, pivot- joints. 1. Hinge-joints. In these the plan of structure and mode of working bear a close resemblance to a common hinge. They allow of only two motions a backward and a forward one, just as a door moves on its hinges. Joints of this kind form the most numerous class in the body. Call upon the children to give illustrations of this kind of joint, such as the elbow, the knee, the wrist, the ankle, and the joints of the fingers and toes. Point out the difference in movement between the fingers and the thumb. The thumb has not only a backward and forward movement such as the fingers have ; it can move also from side to side at right angles to that. In either direction the movement is that of a hinge, and we usually describe this as a double hinge-joint. Make it clear that this double joint is situated not in the thumb itself, but in the long bone which connects the thumb with the wrist. This bone is jointed to one of the wrist-bones by a double hinge-joint. 2. Ball-and-socket joints. In joints of this class one bone has a rounded knob a sort of ball at its extremity, the other a cup-shaped hollow just large enough to receive it. The ball of the first bone plays freely in the hollow cup of the other, and this allows very extensive movement in any direction Illustrate the action of such a joint by some mechanical contrivance of a like nature e.g. the hanging gas-pipe or chandelier. These are often made to hang by a ball-and-socket joint, and may be moved in any direction. Tell that the arm is jointed to the shoulder and the thigh- bone to the hip by a ball-and-socket joint. The bone of the arm and the bone of the thigh have each a round knob or ball, which fits and plays freely in a corresponding cup or socket in the shoulder-blade and hip- bone respectively. LES. xxxi THE JOINTS 213 Put a boy through a variety of movements with the arms. Could we do the same with the legs ? Lead the class to see that the movements in the two cases are alike in character, but that they differ in extent. We cannot swing our legs as freely as we can our arms. Why is this 1 Tell that the cup in the hip-joint is very deep, and the ball of the thigh-bone is deeply lodged in it. Consequently the movement there is not so extensive as at the shoulder-joint, where the cup is shallow. 3. Pivot -joints. Explain what the arrangement is in this kind of joint a round peg or pivot in the one bone fitting into and playing freely in a sort of ring or hollow in the other. The most perfect example of these pivot-joints in the body is in the neck. The skull rests of course on the topmost vertebra. This is provided with a hollow ring, into which fits an upright peg or pivot of the second vertebra. Make one of the children turn the head first to the right and then to the left. Tell that in this movement it is the topmost vertebra that moves round on the peg of the second; and that in moving round, it carries the head round with it. A boy's top spins or rotates upon its peg its peg is a pivot on which it spins. We cannot turn our heads completely round and round in the same direction as the top turns. Why not ? It would tear away and destroy the flesh and all the other parts near the joint. In the pivot joints the rotation is only partial. III. How THE JOINTS WORK SMOOTHLY Call attention to some piece of machinery at work e.g. a sewing-machine. All must go smoothly and easily. There must be no rubbing, no grating. If we examine it, we shall find that the working edges 214 OBJECT LESSONS STAND. i\ are smooth, polished steel ; and we know that the machinist is careful to keep these smooth surfaces well oiled from time to time, so as to make them glide easily over each other and to prevent the slightest friction. Now let us look at these joints in the bones. Show a suitable bone, if possible. The whole of the working surface of such bones is covered with a smooth, shiny coating of gristle. The two bones which form the joint are thus able to glide smoothly one over the other without friction. Show the smooth edges of the bone, and scrape away some of the shiny coating of gristle with a knife. Then, too, each joint is completely enclosed in a sort of bag, made of a very delicate skin or membrane. This bag, which is known as the synovial sac, has the power of preparing and pouring into the joint a peculiar oily fluid, resembling somewhat the white of egg. We call the fluid synovia, and its business is, of course, similar to that of the oil with which we lubricate the working parts of machinery. Nature stores up her own joint oil in these synovia! sacs, just where it is wanted, and in the very quantity required. What happens if these joints become deprived of their synovia ? The working edges of the bones grate painfully one upon another, with a noise like the creaking of a wicker basket. IV. LIGAMENTS Why do the bones not slip out of their places very often? Tell that they are held in their places by strong gristly bands, called ligaments. The word ligament simply means a band which holds or binds one thing to another. Refer to the strong ligaments which bind the joints of a fowl, a goose, or a turkey together. Difficult to carve these birds. Why? LES. xxxn MUSCLES, NERVES, AND SKIN 215 Lesson XXXII MUSCLES, NERVES, AND SKIN I. MUSCLES INTRODUCE the new lesson by making the children talk of the solid, bony framework as a piece of machinery, capable of an almost endless variety of movement. Our next business will be to find out what it is that sets these bones in motion. Tell one of the boys to hold up his arm in front of the glass. Compare the round, shapely limb with the bony framework on the large wall-sheet. Notice that the bones as seen in the skeleton are small in the middle, and swollen into a sort of knob at the extremities, so as to form the joints. The arm itself, however, is largest in the middle, and gradually becomes small towards the extremities. It is the flesh that gives roundness and beauty to the body. We must now see what this flesh is. 1. What the muscles are. If the white skin all over the body were stripped off, the red flesh would be seen beneath. This red flesh is muscle. Think of a piece of lean beef. It is of a reddish colour. This redness is due to the blood in the flesh. Soak it in water, and the blood from it will tinge the water. The muscles are the agents by which every movement we are capable of performing is carried out. Hence where the greatest power of movement is required there we find the largest and strongest muscles. In some parts of the body, as in the legs and arms, the muscles are placed in large, solid-looking masses round the bones. In other parts we find the muscles extended between the bones. The skull has a very slight covering of muscle beneath the skin. Why is this ] The reason is that the bones of 216 OBJECT LESSONS STAND. i\ the skull do not move, and therefore have no need of muscles. 2. Structure of a muscle. A piece of lean flesh from the body of any animal, if examined, will be found to consist of separate bundles of flesh arranged side by side, in such a way that each has the power of moving or sliding about independently of the rest. These separate bundles of flesh are the muscles. A muscle consists of a thick, solid middle part, which is called the belly, and two tapering ends. As a rule the muscle is attached to two bones one fixed, the other movable. They are not joined directly with the bones. Their tapering ends usually terminate in tough, whitish, leather- like cords, which we call tendons. It is the tendon which binds the muscle to the bone. 3. How the muscles act. But we have not yet seen how the muscles move the bones. Tell that the muscles are very elastic; but theirs is the elasticity of sponge or cork, and not the elasticity of india- rubber. Why do we say that india-rubber is elastic ? How does cork or sponge differ from it 1 The cork and the sponge contract or shrink up with pressure, and expand or spring back when that pressure is removed. The india- rubber expands when pulled, and contracts or shrinks up when let go. So then the muscles resemble in their elasticity sponge and cork, and contract when interfered with. Take two bars of wood, and join them loosely together at one end by a sort of peg. Take now a piece of rope and attach it to the ends of the two bars, so as to keep them separated at a certain angle. The bars represent two bones, the rope the muscle attached to them. Now wet the rope, and note the result. The wetting causes the rope to contract, or swell up and shorten. As it does this it pulls up one of the bars. Apply this to the great biceps muscle in front of the upper LES. xxxii MUSCLES, NERVES, AND SKIN 217 arm ; to the closing of the hand ; the drawing up of the knee, and a fairly correct idea of muscular action will be formed. When I wish to draw up my arm, the great biceps muscle contracts ; and as this is connected with both the upper arm and the fore-arm, it draws the latter up. There are more than 500 distinct muscles in the body. II. NERVES Refer to the skull as a hollow, bony box containing the brain. Tell that in the floor of this box, and just where it rests on the vertebral column, there is a round hole. In the vertebra itself, immediately below, and in every one of the vertebrce in the column, is a corresponding hole. These standing one above the other, as we might stand a string of reels, form a long, continuous tube from the bottom of the column upwards to the skull, and into the skull itself. We call this tube the vertebral or spinal canal. The skull, as we have seen, is filled with the brain. Some of the brain extends downwards from the skull and fills the spinal canal. It is known as the spinal cord. Obtain a sheep's brain, and cut it up before the class to show the kind of substance. It is very different from the solid flesh of the muscles. From the brain and spinal cord extend outwards through the body long, white, silvery-looking threads the nerves. Some of these nerves spread themselves all over the surface of the skin, and it is through them that we are able to feel the hardness or softness, the heat or cold, the roughness or smoothness of various bodies. Others spread themselves among the muscles of the body. They are the foremen or overseers who set the muscles to work. Tell that when we wish to lift our hand or turn our head, it is the nerves that make the muscles do our bidding. If the nerves in our arm were destroyed or injured (as they are some- 218 OBJECT LESSONS STAND, iv times by paralysis), however much we might desire to lift the limb, we should find ourselves unable to do it. But whence do the nerves get their orders 1 The brain is the chief centre; the nerves may be compared to a multitude of telegraph wires, extending into every part of the body. They are continually carrying messages to and fro. Illustrate simply in this way : A hot body, say a hot iron, is brought near a person's hand without his seeing it. Instantly he draws his hand away. Simple as this seems, the nerves have been very busy. They first carried up a message to the brain to say that the hand was being burned ; and then they brought back from the brain an order to the muscles to draw the hand back. Explain that, in addition to this, the brain is the seat of the will, the intellect, and memory, of the affections and the emotions. It is by the brain and its nerves that we see, hear, smell, taste, and touch. III. THE SKIN The whole of the external surface of the body is covered with a coat of its own, which we call the skin. Tell that the internal parts of the body are also covered with a somewhat similar lining ; and call attention to its difference in appearance, as seen on the lips. The skin not only binds together the bones, muscles, nerves, and all parts of the body, but also serves to protect them from injury, dirt, and the action of sun, rain, and frost. We shall deal with the structure and work of the skin in a later lesson ; and we shall then learn that it is a very complex part of the body. LES. xxxin CIRCULATION OF THE BLOOD 219 Lesson XXXIII CIRCULATION OF THE BLOOD I. MEANING OF THE TERM REFER to the preceding lessons. Lead the class to tell of the various parts of the body the bony skeleton, the muscles, the skin, the nerves all doing their own special work for the general good. Explain that all these parts of the body require to be fed and nourished, or they cannot do their work. They are nourished by the blood. The great work of the blood is to feed the tissues in every part of the body. This explains why blood is found in every part of the body. We cannot prick ourselves even with the sharpest of needles without drawing blood. Lead the children to tell that there is no blood in the hair and the nails. They do not bleed when we cut them. One of the first things to learn about this blood is the fact that it does not rest stagnant as water stands in a bottle, but that it is always on the move. It flows through the body in a continuous stream, round and round, returning to the same spot again and again. This incessant onward flow of the blood, round and round, through the body, is known as the circulation of the blood. Lead the class to see that as the blood flows, or circulates, in this way, it must have certain distinct channels through which to flow. All the blood in the body is contained in pipes or tubes, which we usually speak of as blood- vessels. Take the arm and hand as an illustration. Lead the class to see that there must be a flow of blood down the arm to the fingers, and a return flow up the arm. Explain that those vessels which convey blood down the arm 220 OBJECT LESSONS STAND, iv towards the hand are known as arteries ; those which carry it back are called veins. But why should the blood flow at all ? What is it that keeps this stream incessantly on the move ? Tell that this is the work of the heart. We are now going to find out what the heart is, and how it does its work. II. THE HEART The heart is a pear-shaped organ, about the size of one's fist. It is situated in the middle of the thorax or chest (the upper portion of the trunk). It is made entirely of muscle, and contains four chambers of equal size. The two upper chambers are called auricles, the two lower ones are named ventricles. Thus there is a right and a left auricle, and a right and a left ventricle. Explain that the floor of the auricles forms the roof, so to speak, of the ventricles. Each auricle communicates with the ventricle below it by means of a hole in this floor ; but there is no communi- cation of any kind between the right and left sides of the heart. What name did we give to those blood-vessels which convey the blood up the arm from the hand 1 Veins. In all parts of the body there are vessels of this kind veins, and their work is to convey the blood towards the heart. They unite with each other, on their way, forming larger and larger vessels, as they get nearer and nearer to the heart. All the blood from the upper part of the body is brought back to the heart at last by one great vein ; and all that from the lower part by another. These two great veins open into the right auricle of the heart. Remind the class next that the heart is made entirely oj muscle. Lead them to tell the nature of a muscle, and how it ads by contracting, when interfered with. It is tlie nerves LES. xxxin CIRCULATION OF THE BLOOD 221 which control the muscles all over the body, and keep them at their work. There are certain nerves whose business it is to act aa overseers of the heart and see that it does its work. How vigilant these nerve -overseers must be ! The heart, under their control, begins its work at the very commencement of life, and never rests for a single moment till death comes. This work is always done in one way. Auricles and ventricles do not work together. Both auricles begin to contract at the same moment ; but while this is going on, the ventricles, left to themselves, expand. The instant the auricles cease working, the ventricles begin ; but while the ventricles contract, the auricles are expanding. Hence when the auricles are contracted to their smallest size, the ventricles are stretched out to their fullest ; and when the ventricles, in their turn, have finished their contraction, the auricles are expanded to their utmost. Fill a hollow india-rubber ball with water, and then squeeze it in the hand to show what must happen. The contraction drives out the water from the ball. Explain that this will roughly illustrate what takes place when the chambers of the heart contract. The auricles at the moment they commence to contract are stretched to their fullest extent, and have been filled with blood from the two great veins. The act of contracting must drive the blood out of the auricles. It cannot return, because of the great body of blood behind in those veins. It flows onward into the right ventricle, which has expanded to receive it. The ventricle is no sooner filled than it begins in its turn to contract, and so to drive out the blood. As the ventricle contracts it closes the orifice between it and the auricle above, so that the blood is prevented from returning. It finds an easy passage along a great vessel, which opens out from the ventricle, and leads away from the 222 OBJECT LESSONS STAND, iv heart, to the lungs. This is the course the blood now takes. Return for a moment to the vessels in the arm which carry blood down to the fingers. We called them arteries. Explain that they are really carrying the blood away from the heart. All vessels which convey blood from the heart are arteries. The great vessel which leads from the right ventricle to the lung's is called the pulmonary artery. Explain why. The blood after passing through the lungs is brought back to the heart by other vessels. What shall we call them ? Veins. They are known as the pulmonary veins, and they open into the left auricle. Explain that the rest is just a repetition of what took place in the right side of the heart. The auricle expands, and receives the blood, and when full begins to contract. The contracting drives the blood from the left auricle into the left ventricle through the hole between them. When the ventricle in turn contracts, this hole closes, and the blood cannot return. There is a great artery the largest artery in the body opening out from the left ventricle, and the way through it is open. Hence the blood flows along into this great vessel. This artery is the aorta. It branches out into smaller arteries and so carries the blood into all parts of the body. The smallest of these branching arteries break up at last into still finer tubes, in. all parts of the body. These are so fine that they are the merest hair- tubes. They are called capillaries, from a Latin word which means " a hair." These unite again and form the commencement of the veins so that the capillaries form the connecting link between the smallest arteries and the smallest veins. LES. xxxiv DIGESTION 223 Lesson XXXIV DIGESTION I. THE BLOOD WHAT IT is OUR last lesson showed us the blood as a stream flowing or circulating round and round through the body. We must next learn what the blood is, and what work it does as it flows along. Explain that every act of our daily life destroys some part of the substance of the body. The muscles as the movers of the body, the brain as the centre of thought and intellect, the eyes, ears, nose, skin, every part of the body, performs its work, but in the very act destroys some of its own substance. This is why we feel faint and tired after exertion. We have a desire for food. We are hungry. If we were kept without food, our bodies would shrink in size, and we should become weaker and weaker. The tissues of the body must be renewed and built up again as they are destroyed, or the body would lose in weight and strength. The blood does this work of building up. But whence does the blood get its materials for this work? The food which we take supplies the materials. The blood is actually made from the food which we eat. The process by which our food is changed into blood fit to nourish the body and build up the worn-out tissues is digestion. We may call digestion the work of blood- making. II. THE WORK OF BLOOD-MAKING Lead the class to think about the blood-vessels which vje described in the last lesson. The smallest of these the capillaries are tubes finer 224 OBJECT LESSONS STAND, iv than the finest hairs ; yet the blood in its course through the body must flow through them. The solid bread, meat, pudding, potatoes, in fact all our food, must be broken up into such extremely fine particles that it may find its way into these delicate pipes and flow along them in the stream of the blood. The food must not merely be broken up, it must be dissolved before it can be of any use in the body. This dissolving of the food is what we mean by digestion. 1. In the mouth. Lead the class to tell that the first part of the process of digestion takes place in the mouth. We call it mastication or chewing. Let them describe what goes on. But this grinding up the food by the teeth is not all. Lead them to tell that as ihe food is crushed up, it becomes moistened in the mouth. The fluid which moistens the food is called "saliva," and is poured out from the lining membrane of the mouth. Saliva has the power of changing starch into sugar. Starch is insoluble, but sugar is a soluble substance. Elicit from the children that bread and many other things which we eat contain starch. Lead them to show by experiment the insolubility of starch and the solubility of sugar. These starchy foods, being insoluble, would be useless. The saliva changes the starch into sugar ; the sugar is soluble, and is easily absorbed and dissolved in the blood. 2. In the stomach. When the food has been properly masticated, it is swallowed. It passes down a tube at the back of the mouth, known as the gullet or food-pipe. This tube carries the food into the stomach. Show these on the wall-sheet, or by a black-board sketch. The stomach is a strong, muscular bag or pouch, situated in the upper part of the abdomen, immediately below the diaphragm. By means of its muscular walls, it is constantly at work contracting and expanding, especially when it contains food. These movements in LES. xxxiv DIGESTION 225 the bag roll and churn the food about, and so help to still further break it up. While this is going on, a fluid is constantly oozing out from the inside coating of the stomach, and mixing with the food. This fluid, is known as the gastric juice. Explain that this gastric juice is meant to do a similar work to that performed by the saliva in the mouth ; but it mil not act upon starches. It dissolves lean meat and the glutinous parts of bread, and so renders these substances fit to be absorbed into the blood. Explain that the inner lining of the stomach is crowded with a close network of blood capillaries, and these vessels are always at work sucking up the fully dissolved matters of the food. 3. In the intestines. The stomach at its right-hand lower extremity tapers off to a narrow pipe, and this forms the commencement of a long tube the intestines. The first part of the intestines is smaller than the rest. We call it the small intestine. This tube is folded and doubled many times upon itself. Explain that the entire length of the intestinal tube, if it were stretched out in a line, would measure between five and six times the length of the person ; and that it would be impossible to pack it in the small space provided unless it were folded up in this way. Describe briefly the liver and its position just above the junction of the small intestine with the stomach. The liver is a great gland, and its work is to prepare a special fluid the bile which is required for the com- plete digestion of the food. Explain that there are a great many organs in the body engaged in preparing fluids for future use; and they are all called glands. The saliva and the gastric juice are prepared by glands. The food, as it is being churned about in the stomach, is constant^ giving up the fully dissolved portion to the blood- vessels all round. But all the fat and oily parts of the VOL. II Q 226 OBJECT LESSONS STAXD. iv food still remain undissolved. They cannot be taken into the blood in that state ; they pass out of the stomach unchanged, into the intestine. The bile, which is prepared iu the liver, is poured into- the small intestine, near its junction with the stomach. The food therefore, as soon as it passes from the stomach into the intestine, becomes mixed with bile, and it is this bile which dissolves the fatty parts of the food, and renders them fit to be absorbed by the blood. As the food passes along the intestinal canal, these dissolved fats and all that is of use are absorbed into the blood, and only the useless, undigested remainder is discharged from the body. N.B. The actual process of absorptionby the villi,indeed every- thing intricate has been purposely omitted. The object of this lesson has been to give merely a broad notion of the work of digestion. The subject will be more fully dealt with in a later stage. Lesson XXXV RESPIRATION I. ARTERIAL AND VENOUS BLOOD COMMENCE by directing the thought of the class to the circulation of the blood. Lead the children to describe the flow of the blood from the heart along the arteries ; the breaking up of the smallest arteries to form capillaries ; and the return of the blood from the capillaries through veins to the heart. The blood sent out by the heart along the arteries to the capillaries is a bright scarlet colour, and fit to do its proper work in the body. We call it arterial blood. Why ? This blood passes through the capillaries, and is collected up again by the smallest veins, which unite into larger and larger vessels, and at last carry the blood back again to the heart. LES. xxxv RESPIRATION 227 The blood which is taken back to the heart by the veins is of a dark purple colour. We call it venous blood. Why ? In its passage through the capillaries it becomes loaded with impurities from the worn-out tissues. These impurities not only change the Colour of the blood, but they poison it, and render it unfit for its work. The blood which is brought to the right auricle of the heart by the great veins is impure. It is not only unfit to do its proper work, but it would poison the body if it were sent out from the heart again in that state. One of the principal poison-matters taken up by the blood in the capillaries is the gas carbonic acid, with which our lessons have already made us familiar. This poisonous gas must be removed from the blood before it can again do its proper work in the body. Lead the class next to trace the blood from the right auricle to the left ventricle. Show them that the blood in both chambers on the right side of the heart is dark purple, venous blood. What becomes of it after it leaves the right ventricle. It is carried away to the lungs by the pulmonary artery, which branches into two immediately after leaving the heart, one branch going to each lung. Why is this called the pulmonary artery ? Pulmonary comes from a Latin word pulmo, which means " lung." It is the artery which carries the blood to the lung. What kind of blood does this artery carry away from the heart 1 Dark purple, impure blood. What kind of blood have we already found in arteries ? Bright scarlet blood. Explain that this is the only artery which carries dark purple, venous blood. How is the blood brought back again to the heart from the lungs ? By the pulmonary veins. Explain that the blood which these veins carry back to the heart is no longer dark purple, and impure, but pure, bright scarlet blood. 228 OBJECT LESSONS STAND. IT Lead the children, as before, to tell the kind of blood usually found in veins. Here we have veins bringing bright, scarlet blood to the heart. They are the only veins which do so. To which chamber of the heart is the blood now brought ? To the left auricle. Show that both chambers on the left side of the heart contain this arterial blood. The pulmonary artery took away from the heart dark venous blood, the pulmonary veins bring back to the heart bright arterial blood. The change takes place in the lungs. II. THE LUNGS The lungs are two large organs situated in the thorax, one on each side of the heart. They occupy the whole of the space in the thorax which is not taken up by the heart and its great blood-vessels. Explain that these are the organs which the butcher calls , the lights. Sheep's lights may be seen hanging up in the butcher's shop. The lungs are of a pinkish colour, soft and spongy, and very elastic. In the body they are attached to the walls of the thorax and to the diaphragm by a membrane the pleura. Call attention to the hard gristly pipe which passes down- wards in front of the throat. This is the windpipe ; it is sometimes called the trachea. Explain that it commences at the back of the mouth and nasal passages ; passes into the thorax ; and then splits up into two one pipe going to each lung. Each of the branching pipes is called a bronchus. In the lung the bronchus splits up again and again into smaller and smaller pipes the bronchial tubes, the smallest at last ending in little bags or cells. These are known as air-cells. The whole substance of the lungs is simply a mass of these air-cells. Explain the reason for the name air-cells. These little cells are in direct communication with the air all round us. LES. xxxv RESPIRATION 229 When we breathe, air passes down the windpipe, the bronchus, the bronchial tubes, into the air-cells. Now let us go back to the pulmonary artery which brings to the lung dark impure blood to be purified. This artery (like all others) splits up in the lung into smaller and smaller vessels, ending at last in capillaries. The capillaries spread themselves all round the walls of the little air-cells. The air-cells are full of air, the capillaries all round them are full of this bad blood. Two things then take place. The blood gives up its impurities to the air in the air-cells, and takes something from the air in exchange. In one of our lessons I showed you a little experiment by setting a boy to breathe through a tube into a glass of lime-water. What took place? The lime-water became milky- looking. What did that prove ? That carbonic acid had been put into it. Whence did this carbonic acid come ? From the boy's breath. The blood is purified in the lungs by giving up to the air-cells the carbonic acid which it has absorbed in the body. Lead the children next to talk of the presence of oxygen in the air, and the important part it plays in all combustion. The air in the air-cells contains oxygen, and this oxygen the blood absorbs in exchange for the carbonic acid which it gives up. The incessant act of breathing is merely to drive out from the air-cells the carbonic acid which they take in from the blood, and to keep them filled with fresh pure air containing plenty of oxygen. 230 OBJECT LESSONS STAND, iv LESSONS FROM ZOOLOGY Lesson XXXVI THE ANIMAL KINGDOM I. INTRODUCTION LEAD the class to think of the great number and variety of animals they have seen and know. Tell of countless multitudes which tliey have never seen and are never likely to see some living on the earth, some burrowing beneath its surface, others living in the water, others in the air. These form the animal kingdom. It is very important that we should know as much as possible of this vast array of living creatures, both for our pleasure and our profit ; but the first step towards studying them is to arrange them in some definite order. Refer to the necessity for a proper classification in other matters. Children are classified to be taught successfully ; work- men by their masters to work properly. A general classifies his soldiers, a librarian his books. Nothing can be carried out successfully without order in arrangement. Let the class think of some of the animals of our former lessons. Cats, dogs, sheep, horses, birds, snakes, frogs, and fishes are all alike in one respect, and all differ from such animals as bees, butterflies, beetles, and spiders in that same one respect. Run your hand down the middle of your back. You feel a ridge of bony knobs or projections. This ridge is your backbone. We ourselves are like the cat, dog, sheep, bird, snake, and fish in this respect. We and they have a hard, LES. xxxvi THE ANIMAL KINGDOM 231 bony, internal skeleton ; and the most important part of this skeleton is the backbone. You can see and feel it too along the back of some poor, ill-fed dogs or horses, because they are so thin ; and when you eat a herring 1 or some other fish you leave the backbone on the plate. Bees, butterflies, beetles, spiders, and hosts of other animals have no backbone at all. It is this distinction which enables us to make our first great classification of the animal kingdom. We arrange all animals in two great groups those having a backbone, those without a backbone. II. VERTEBRATES AND INVERTEBRATES The word backbone is misleading. Why ? Because it is not the name of a single bone a bone all in one piece. The backbone is really made up of a great number of separate, bony rings, all fitting closely together, but capable of moving to some extent. Illustrate by threading a number of wooden reels on a string, and show that although each individual reel moves only to a slight extent, there is great flexibility and freedom of movement in the whole chain of bones. The backbone of a little boy is formed of thirty-three separate bony rings fitting together in this way. He can easily bend his back without putting it out of joint. By the time he reaches manhood, however, several of the lower rings will, for the sake of strength, have grown together. A man has only twenty-six separate bones in the column. Most of the animals we see around us have more separate bony rings in their backbone than we have in ours. I think you can tell me of some animals which have a very great number. Snakes. Yes. One great snake, the python, has no less than 400. We have a particular name for these separate bones which form the backbone. We call them vertebrae. 232 OBJECT LESSONS STAND. :v Verio is Latin for " I turn " ; and by means of these bones we and other animals can turn, move, or bend our backs and necks freely. As the backbone is made up of vertebra, it is sometimes called the vertebral column, and all animals which have a backbone are called vertebrate animals, or vertebrates. They form the first sub-kingdom of the animal world. The other sub-kingdom comprises all animals which have not a backbone. They are called invertebrate animals, or invertebrates. In means "not." Lesson XXXVII NATURE OF THE BACKBONE I. THE VERTEBRA WE have called these separate bones rings. Let us see what that means. Show, if possible, a few vertebral bones. It would not be a difficult matter to obtain what is required from the butcher. The bones must be boiled, and the fleshy and gristly parts removed. They may then be kept for reference in the school museum. Failing these larger bones, the vertebrce of a rabbit will serve the purpose equally well Point out that each bone is pierced through, from top to bottom, with a rounded hole. Let the children examine. Tell that when the bones are fitted together, tJtese holes also fit to each other, so as to form one continuous tube or canal. This canal extends from one end of the vertebral chain to the other, and is known as the vertebral canal or spinal canal. Eefer to the ridge of knobs or projections felt down the middle of the back. Show the separate vertebrce, and call attention to the three projections or processes. LBS. xxxvii NATURE OF THE BACKBONE 233 Tell that the word " spine " means a projection ; that it is the middle spine which is felt along the back ; and hence the lack- lone itself is sometimes called the spine, and the canal, the spinal canal. II. THE SPINAL CORD The upper part of this spinal canal opens out into the great cavity of the skull. The skull is a sort of bony box made to hold the brain. All animals with a backbone have also a brain, although none have so great a brain as man. Part of the brain stretches downwards by means of a hole in the bottom of the skull and runs through the spinal canal. We call it the spinal cord. It is the great nerve of the body. The brain and spinal cord are the overseers or foremen to see that all the rest of the body does its proper work, at the proper time, and in the proper way. All vertebrates have a brain and spinal cord. III. How THE VERTEBRAE ARE JOINED Refer to earlier lessons, and elicit a description of the manner in which the vertebra are joined in different animals. In man and most of the animals around us the vertebrae are joined by pads of elastic gristle or cartilage, which allow limited movement and prevent friction or grating of one bone against another. The vertebrae of a snake are joined by ball-and-SOCket joints. Why? In fishes each vertebra has a sort of Clip or socket on either side, and it is only the rims of these cups which fit together, the hollow being filled with a sort of fluid. Why? In all animals strong gristly bands called ligaments hold the vertebrae together, and keep them in their places. 234 OBJECT LESSONS STAND, iv The separate bones are allowed a certain freedom of move- ment, but the ligaments prevent them moving beyond that limit. Lesson XXXVIII VERTEBRATES LET the dass tell the meaning of the term " vertebrate," its deriva- tion and application. The great sub -kingdom of vertebrate animals (i.e. animals which have a backbone) includes many varieties of creatures. Lead the dass to think of a horse, a pigeon, a herring, a frog, and a snake. These, although belonging to the same great sub-kingdom, are very different one from the other, and it would be impossible to study them in one group. We must find out in what points the various members of the sub-kingdom differ among themselves, and that will help us to a second classification. You have all seen the cat with her kittens; perhaps some have seen the cow with her calf, or a sheep with its little lamb. The mother in each case feeds her young one with milk which is formed in her own body. We say she suckles them. If we put our hands on any of these animals, we feel that their bodies are warm. Why ? Because they have warm blood. The body of a fish or a frog always feels cold and clammy. A bird also feels warm if we take it in our hands. It has warm blood. But it is quite a distinct creature from those we have named. Why ? Birds produce their young from eggs ; and they do not suckle them. Snakes and lizards, frogs and toads, and fishes all resemble birds in producing their young from eggs, and in not suckling them. But they differ from birds in having cold blood. The four-footed animals and birds might then be arranged in one group or class and called warm-blooded LES. xxxvin VERTEBRATES 235 animals ; while the snakes, frogs, and fishes would form another group of cold-blooded animals. It is usual, however, to arrange the vertebrate animals in five classes. I. MAMMALS Boys and girls living in the country may have seen the little calf sucking the milk from its mother's body. The milk comes from "teats," which the little one sucks. The Latin name for "teat" is mamma, and as all animals which suckle their young are provided with teats, we give them the name of mammals. What did we say about the blood of these animals ? It is warm blood. You know too the colour of their blood. It is red. If we took the heart of a sheep, a horse, a rabbit, or any one of these mammals, we should find it to consist of four distinct chambers. Mammals all breathe too as we do, through lungs. We ourselves belong to the class mammals. II. BIRDS Lead the children to think of fowls or other common birds. How do they rear their young 1 Birds of all kinds lay eggs, and sit close upon them to hatch them with the warmth of their own body. The little ones break the shell, and come out when fully formed ; and the parent-bird feeds them, but not with milk from her own body. She searches about for little morsels of solid food, which from the first the young ones are able to eat. Birds, like mammals, have two pairs of limbs ; but the front pair are specially fitted for flying. We call them wings. Mammals differ from each other in the kind of 236 OBJECT LESSONS STAND, iv covering they have ; but all birds are clothed with feathers. Birds, like mammals, have red, warm blood; they breathe through lungs ; and the heart consists of four chambers. III. REPTILES The next group will include snakes, lizards, tortoises, turtles. Show good pictures of these animals. The word "reptile" means "creeping thing." It is not a good name, for all these animals do not creep. Tell of the agile little lizards, the great crocodiles, and the alligators of the tropics. Reptiles produce their young from eggs; but they have cold blood, although they breathe through lungs ; and the heart has generally three chambers. Some of the more active and vigorous among the reptile family have four chambers in the heart. That is to say, there is a partial division of the ventricle, which amounts to the same thing. IV. BATRACHIA We have already had this word in our earlier lessons. What does it mean ? Frog-like animals. Frogs, tods, and newts form a class by themselves. They are hatched by the heat of the sun from eggs which the mother has laid in the water. They commence life in the water, breathing like fishes, through gills. The heart has only two chambers an auricle and a ventricle. What is a young frog called ? A tadpole. What becomes of it? It gradually loses its fish-like form, and develops lungs instead of gills, and legs to walk and hop about on^the earth. It then leaves the water and enters on a new life, breathing air through lungs like other land-animals. The blood of these animals is cold, and the heart of the fully- developed frog has three chambers two auricles and one ventricle. LES. xxxix THE INVERTEBRATES 237 V. FISHES Fishes produce their young from eggs. They are cold- blooded animals specially fitted for life in the water. They breathe all their life through gills, and the heart has only two chambers. The body is covered with scales, and they have fins instead of limbs. Lesson XXXIX THE INVERTEBRATES WE are now going to study an entirely new sort of creatures the invertebrates. Who knows why they have this name ? They have no backbone. Remind the class that there is also no internal skeleton; no skull with brain and spinal cord, such as vertebrates have. I. BLOOD But there are other points of difference. Vertebrates have red blood. Invertebrates have colourless * and cold blood. * N.B. The blood of the earth-worm is red, but without red coi-puscles. II. MOUTHS Think of a mammal, a bird, a reptile, a frog, and a fish. How do they move their mouths? Vertically up and down. Some of the invertebrates have no jaws. Whenever they have, they always move them horizontally. Watch a beetle or spider eating, and see for yourselves. III. BREATHING ORGANS We have seen that some of the vertebrates breathe through lungs, others through gills. But how does the air reach these breathing organs ? It is taken in at the mouth. 238 OBJECT LESSONS STAND, iv Remind the class that even in the case of a fish, water, with air dissolved in it, is taken in at the mouth, and passed back- ward over the gills which rob it of the air. Not one single invertebrate uses its mouth in breathing. Some breathe through holes in their sides ; others through long slits in the necks ; others again through their tails. They have neither lungs nor gills. IV. LIMBS Lead the class next to think of the limbs of the vertebrates, and show that none have more than four true limbs. Those invertebrates that have limbs usually have more than four. Thus all insects have six legs ; spiders eight ; shrimps, crabs, and lobsters have ten. Many of the insects in addition to six legs have two pairs of wings as well. V. YOUNG INVERTEBRATES Lastly, lead the class to think of the young of the various members of the vertebrate family. You would not mistake a kitten for a young snake, a bird, a fish, or even some other mammal. Why] Because the young ones always resemble their parents. The baby-boy has the form of a man ; a calf is a little cow ; a chick is a tiny hen. They grow bigger as they grow older, that is all. Remind the class of the wonderful exception in the case of a frog. A young invertebrate is often a very different sort of creature from its parents. Refer to the lesson on insects, and lead the class to tell of the larva or grub that emerges from the egg, and is totally unlike its parent. Compare the caterpillar and the butterfly ; the ugly LES. XL CLASSIFICATION OF INVERTEBRATES 239 grub or maggot of the lee, common fly, or wasp, with its parent insect ; the crawling water-grubs of the gnat or dragon-fly and the perfect insect. The egg produces the grub, the grub becomes the pupa, the pupa changes to a perfect insect. Lesson XL CLASSIFICATION OF INVEETEBRATES The invertebrates are divided into six great sub- divisions. I. SOFT-BODIED ANIMALS Show a snail and a slug as types of this class. They all have a soft fleshy body, sometimes naked and defenceless, like the slug; sometimes covered with a protecting shell, which the creature manufactures for itself. Indeed the shell is really part of the animal ; the animal cannot leave it. It is not a mere house. The vast majority of these soft-bodied animals have their home in the water. They are found in every part of the world, abounding in ponds, lakes, rivers, and seas. Some, such as the cockle, bury themselves in the sand ; some bore holes for themselves in the soft rocks ; others, like the mussels, are found in the shallows near the shore ; but the vast majority make their dwellings in the very depths of the ocean. Show a picture of some of these in their living state. The shells, which most of them make for themselves, are sometimes in one, sometimes in two pieces. Show a whelk, a periwinkle, and a cowrie shell, and compare it with the shell of the snail. These are all in one piece. We call them uni-valves. Tell the meaning of the name. Show next a mussel and an oyster. By plunging them 240 OBJECT LESSONS STAND, iv in boiling water the shells will open. Point out the two parts of the shell joined on one side by a hinge. We call them bi-valves. Why ? Scallops and cockles also belong to this group. Show these shells. Returning to the slugs and snails, tell that these, although originally water animals, have been fitted to live and breathe on land. They breathe through long slits in the neck. Tell of the broad fleshy foot on which the animal glides slowly along, and of the many rows of teeth on the upper lip, acting as a rasp to grind the vegetable food on which it lives. II. JOINTED ANIMALS These are countless in number. Their bodies are formed of ringed segments, and their limbs are jointed and in several parts. Refer to the earlier lessons on insects and spiders, and lead the class to see that they belong to this great group. Let them tell some of the characteristics of insects, and distinguish tJiem from spiders, thus : Insects have six legs; spiders have eight. The body of the insect is in three parts ; that of the spider is in two. The segments are always easily seen in the insect, but in the spider the coat appears to be soft, smooth, and leathery. Help the class to give examples of common insects, e.g. beetles, cockroaches, crickets, butterflies, moths, bees, wasps, flies, ants, earwigs, gnats, grasshoppers, and so on. Tell that besides insects and spiders this great class includes shrimps, lobsters, crabs, centipedes, and millipedes. The two last may often be seen under old boards, or hidden away beneath dead leaves and stones in the garden. Tell the reason for iheir name. Show that in all these the ringed segments and jointed limbs are to be found. LES. XLI MAMMALS 241 III. WORMS Take as an example the common earth-worm. Lead the class to tell what they can of its form, nature, and habits. Besides this creature, the group includes sea-worms, lug-worms, leeches, and tape-worms. IV. STAR-FISH Show a picture of a dried specimen. Describe its form, and tell briefly of its life in the water. But it is not properly a fish. This is a comparatively small class. It includes, besides this example, sea-urchins, sea-cucumbers, and others, all of them having something of this star-like pattern. V. The next class includes jelly-fish, corals, sea-anemones all water animals. Show pictures of some of these. VI. The last sub-kingdom comprises the lowest form of animal life. We may call them the first animals. The best known of this type are the sponges. Lesson XLI MAMMALS ANIMALS which suckle their young form a very large and important class. They comprise individuals which differ from each other in nature, habits, food, and therefore in structure. Mammals are divided into orders. VOL. IT Pv 242 OBJECT LESSONS STAND, iv I. MAN AND MONKEYS The scientific name of this order is primates (the chief or the first). The animal man stands alone and forms the sub-order bimana. He is the only two-handed animal. The monkeys make the nearest approach to man, although they differ greatly among themselves. Show a picture of one of the great apes. Call attention to the four hand-like feet, each with an opposatte thumb. This distinction places them in a separate group or sub-order quad- rumana = four-handed animals. Lead the class to see, however, that it is not merely the possession of two hands instead of four that separates man so immeasurably /row. the leading group of the brute creation. Call attention to the head of the ape in tJie picture, and then tell of the great size and power of the brain in man. Intellect makes man more than a mere animal. Man too is the only animal that walks and stands erect. The four-handed animals all move about with an awkward stooping gait, resting their fore -hands on the ground at each step. Call attention to the great length of their fore-arm, which provides for this mode of locomotion. Can you think of any reason for this four-handed structure ? This is no mere accident, but designed to meet the wants of the animals. The quadrumana live mostly in the trees, and require hands for grasping. The four-handed animals differ among themselves. Some hare tails, others have not; some have bare patches of hardened skin where they sit, others have not ; some have cheek-pouches inside the mouth for storing away food till it is wanted, others have not. These distinctions enable us to arrange the animals in different groups. 1. The apes or man-monkeys have no tails, no LES. XLI MAMMALS 243 callosities, no cheek-pouches. They are the gorilla, the chimpanzee, and the orang-outang ; some of which reach the height of six or even seven feet. The gorilla is extremely savage and powerful. Show pictures of some of these. 2. Baboons have short tails, callosities, and cheek- pouches. Show a picture of a baboon, and call attention to his huge teeth. Baboons are extremely fierce and formidahla 3. The monkeys are smaller and less savage than the other two families. They usually have long tails, cheek- pouches, and callosities. The monkeys of the New World mostly use their tails as a fifth hand in climbing trees and swinging from bough to bough. They may be distinguished from those of the Old World by the position of the nostrils, which open in long slits on the sides of the nose, and not at the end. II. WING-HANDED ANIMALS This order includes the bat family. Show a picture of a bat, and tell that this animal lives on insects which people the air. It must therefore have the power of flight. Show that the two hands are modified to form wings the fingers are lengthened and provided with a thin membrane stretched between them. III. INSECT-EATERS Lead the class to think of the mole. Make them tell that^ it lives on insects, especially beetles and their grubs, on slugs, snails, and earth-worms, which it finds in the ground. Explain that the hedgehog and the shrew are also insect-eaters. Animals of this order are provided with teeth specially fitted for 244 OBJECT LESSONS STAND, iv crushing their prey, and with fore-paws for digging in the ground. Compare these with the former order, which are also insect- eaters, but find their prey not in the ground but in the air. Lesson XLII MAMMALS (continued) I. FLESH-EATERS SHOW that many of the animals already mentioned live wholly or partly on animal food, but most of them can digest and some could live entirely on vegetable food. The next order live entirely on flesh. They are ex- tremely fierce, strong, and swift, for they are hunters ; and they have teeth and claws for seizing and tearing their prey. They form a numerous order, and are usually arranged in groups according to the manner in which they walk. 1. Toe-walkers. These include the various members of the cat and dog families. They walk on their toes only. Let the class mention a few of each family, e.g. the lion, tiger, leopard, panther, of the one family ; and the wolf and fox, of the other. 2. Sole-walkers. These place the flat sole of the foot on the ground at each step. They include the bear, racoon, weasel, otter, and badger families. 3. Fin-walkers. These animals, which include the seal and the walrus, find their food and spend a great part of their lives in the water. The limbs are short and make admirable paddles in the water ; but they allow a very limited and awkward move- ment out of that element. LES. XLII MAMMALS 245 II. GNAWING ANIMALS Refer to the earlier lessons, and lead the dass to mention the rabbit, hare, mouse, rat, squirrel, and beaver members of this order. What is their peculiarity ] Make dass describe the form and use of the chisel-teeth; how they wear and grow and keep a sharp cutting edge. III. TOOTHLESS ANIMALS The members of this order are all foreign animals, living mostly on insects. Some have no front teeth, some no teeth at all. Hence the reason for their name. The order includes the ant-eater, sloth, and armadillo, and the curious ornithorhyriclms of Australia. Show pictures of these. IV. HOOFED ANIMALS Tell that these animals have their toes enclosed in a hard horny case, which we call a hoof. 1. The elephant and tapir form a group of this order by themselves, and are called trunk-nosed animals, from their trunks. 2. Odd-toed animals. The hoof of a horse, ass, and zebra consists of a single toe ; that of the rhinoceros is in three pieces. 3. Even-toed animals. The camel and the giraffe have two toes; the hippopotamus, hog, sheep, goat, ox, deer, and antelope have four toes. In all this group, except the hippopotamus and hog, the two hinder toes are very small. The animals walk on the two front toes only, which form a split or divided hoof, or, as we sometimes call it, a cloven hoof. All these animals with a cloven hoof, except the hog 246 OBJECT LESSONS STAND, iv and hippopotamus, form a distinct group by themselves the cud-chewers. Refer to the old lessons, and elicit some of the chief char- acteristics of this useful group of animals. Lead the class to describe the peculiar form of the mouth, with the pad in place of the incisor teeth in the upper jaw its uses the mode of feeding the form and uses of the four stomachs, and so on. V. WHALE-LIKE ANIMALS This order includes the whale, porpoise, and dolphin. Show a picture ; describe the fish-like form of the body, with short, fin-shaped fore limbs, and the hind limbs entirely wanting. They are mammals, however, and not fishes. They suckle their young, have warm blood, breathe through lungs, and cannot breathe in the water. VI. POUCHED ANIMALS Show a picture of the kangaroo. Describe the curious pouch in which the young are carried for some time after their birth. The kangaroo of Australia and the opossum of America are the chief members of this order. Lesson XLIII BIEDS THIS is a great and important class of vertebrates. Let the children tell the general characteristics. They produce their young from eggs, but do not suckle them ; they have warm red blood ; they breathe through lungs ; and their heart, as in the case of the mammals, has four chambers. LES. XLIII BIRDS 247 They have no teeth, but their hard horny beaks serve instead. Their fore-limbs are modified to form wings. All these facts should be carefully elicited. This great class consists of several distinct orders. I. FLESH-EATERS OR BIRDS OF PREY These are the fierce, powerful, bloodthirsty hunters of the air. They live on the flesh of other animals. They have strong hooked beaks and strong sharp talons to seize and tear their prey. Compare them as hunting animals with the flesh-eating mammals. , . , Tell of their swiftness, their power of flight, and their mode of attack. The order includes the eagle, falcon, hawk, condor, vulture, and owl. , The owl is a night-prowler. The eagle and all the others hunt their prey in daylight. Compare the two. Describe the piercing powerful eyes of the eagle and the hawk, which do not blink at the most brilliant noon-day sun, and are able to sight their Mm from an enormous height. They swoop down with unerring aim from their great height upon birds on the wing, or lambs, hares, a poultry feeding in the field. . Tell next of the owl, and its blinking eyes. BUm throughout the day in hollow trees and any other dark places it can find, and never comes forth till after dusk The eyes of this night-bird are not dull and blinking then. It preys upon rats, mice, and other night animals. Compare it with the cats and other night-prowlers among the quadrupeds in this respect. II. CLIMBING BIRDS Taking the structure of the feet as a means of grouping the other orders, lead up next to the climbing birds. These have strong muscular legs, and each foot has tWO 248 OBJECT LESSONS STAND, iv toes pointing forwards, and two pointing back- wards, to enable the bird to climb and cling firmly and easily. Many of them use the beak as well as the feet in climbing. These birds live entirely in the trees, and do not walk well. Refer to the old lessons, and elicit the names of some individuals of this order, e.g. the woodpecker, cuckoo, parrot, and cockatoo. III. PERCHING BIRDS Take as examples the common sparrow, robin, thrush, and blackbird. They have three toes pointing forwards, and one backwards. liefer again to some of the past lessons, and elicit from the class the peculiar arrangement of the leg and foot tendons, by which the bird is enabled to hold firmly to the branch without any effort ; its own weight being sufficient to keep it secure. Thus the bird rests safely even when asleep. These birds are meant for a tree life, and when on the ground move about with a series of little, short hops. They cannot walk. This order includes most of the common birds of our English woods, as well as the gorgeous birds of paradise and other foreign birds. IV. POULTRY BIRDS OR SCRATCHERS Call attention to tJie habits of the common fowls. They find their food by scratching or scraping in the earth. The feet are strong claws, provided with short, blunt nails, specially adapted for this work. Besides common fowls, this order includes pigeons, doves, partridges, the peacock, pheasant, turkey, quail, and others. These birds feed on grain, which they swallow whole, because they have no teeth to masticate it. LES. XLIV BIRDS 249 The work of crushing the food is done in a strong internal bag, the gizzard, through which all food must pass. Lesson XLIV BIRDS (continued} I. WADING BIRDS THESE birds have very long legs, to enable them to walk in the water. Hence they are sometimes known as stilt- walkers. Why should they want to walk in the water 1 They get their food out of the water. They live on fishes, frogs, and other water animals. Refer to the past lessons, and make the class describe the long necks and bills of these birds, corresponding to their long legs. This order includes the snipes, plovers, lapwings, and herons of England, as well as the stork, crane, bustard, and bittern of other lands. II. SWIMMING BIRDS Take as examples of this order ducks, geese, and swans. Refer to former lessons, and lead the class to describe the webbed feet of these birds ; why they are fitted for a life on the water ; the nature of the bills, with their side fringes, and so on. Tell of marine swimmers, such as the albatross, petrel, gull, penguin, and others. III. EUNNING BIRDS Show a picture of an ostrich. Call attention to the form of the legs and feet. The legs are exceedingly strong and muscular, and the broad, thick toes are pointed forwards. 250 OBJECT LESSONS STAND, iv These birds do not fly ; hence their small wings. The bird uses its wings as balancers in its running. The ostrich is extremely swift, and can run at the rate of 26 miles an hour. The emu and cassowary belong to the same group. Taking next the structure of the beak or bill, we are enabled to make a further classification of birds, especially of many of the smaller varieties. I. TOOTH-BILLED BIRDS The blackbird, thrush, robin, nightingale, and others of our common birds live mostly on worms, grubs, and insects. They are really good friends to the farmer, although they may help themselves to a little of his fruit by way of dessert. These birds have the upper mandible notched near the point, for the purpose of securing their prey. II. WIDE-GAPING BILLS Tell of the swallow skimming swiftly over a pool with its mouth open. What is it doing ? It is catching insects as it flies. Its mouth is slit some distance beyond the upper and lower mandibles, so that it presents a wide-gaping fly-trap when on the wing. Swallows, martins, swifts, and goat- suckers belong to this group. III. CONE-SHAPED BILLS Show a picture of a crow, a sparrow, a linnet, or a lark. Call attention to the short, conical bill. Tell that these birds live mostly on small seeds. Their peculiar beaks are specially fitted for cracking and crushing the seeds. LES. XLV REPTILES, BATRACHIA, FISHES 251 IV. SLENDER BILLS The best examples of these birds are the pretty little humming-birds of South America. They frequent the flowers, some say for the tiny insects in them, others for the sweet juice or nectar which they contain. Whether for one or both of these, the bills have no hard work to do, and hence they are soft and slender. Lesson XLV REPTILES, BATRACHIA, FISHES I. REPTILES These are the creeping or crawling animals. They produce their young from eggs ; but although they breathe through lungs, they have cold blood ; the heart has three chambers instead of four. 1. Snakes. Refer to the lesson on snakes, and lead the class to tell the chief characteristics of these animals. Make them tell of their elongated form, without the least rudiment of limbs; of their mode of progression; of their scale-covered bodies; of their mode of feeding, and the con- sequent adaptation of the jaw-bones and ribs, with their ball-and- socket joints. They have no tearing or chewing teeth. Tell that these animals form the first order of the class reptiles. The order includes huge serpents that crush and mangle their prey in the folds of their powerful bodies before swallowing it, and venomous snakes, which kill their victims by means of their poison-fangs. Lead the children to tell the nature and mode of action of these poison-fangs. 2. Lizards. This order includes a large variety of animals, from the pretty, harmless, little lizards, a few inches in length, which frequent the heaths and sunny 252 OBJECT LESSONS STAND, iv banks in our own country, to the enormous and powerful crocodiles and alligators of tropical regions, which attain to the length of fifteen and twenty feet. The body is always long, and covered with scales, and is supported upon four short legs. There is in most of the family a great length of tapering tail. They are all armed with teeth. Some of the smaller varieties live on insects, others on vegetable food. The giant members of the family live mostly in the water, and prey upon fish and other water animals. The chameleon is a curious member of the family. It lives mostly in the trees, and preys upon insects. 3. Tortoise -like reptiles. The animals belonging to this order have their bodies enclosed in a sort of shell. Show a picture of a tortoise, or, if possible, an actual tortoise-shell. It would be better still if a living specimen could be borrowed for this occasion. Many people keep the common tortoise as a sort of pet. Call attention to the double shell which completely encloses the animal. The flattened under shell, or, as we might call it, the breastplate, is that upon which the animal rests on the ground. It is called the plastron, and is made of hard, thickened skin. It is joined at its edges by the broad, rounded shield, the carapace, which covers the animal. This carapace is really part of the bony skeleton of the animal. All the animals we have hitherto examined possess an internal bony skeleton ; but here we have a creature with its bony skeleton on the outside of its body. Tell that the carapace is really nothing more than the vertebral bones and the ribs, with the spaces between them filled up with horny plates, the whole grown together into a hard, solid shell. Show that the front and hinder parts of this double shell are open to allow of the passage of the head and limbs. Call attention to the peculiar form of tJie head, and the hard 253 LES. XLV REPTILES, BATRACHIA, FISHES horny mouth. This is in place of teeth, which are wanting in these animals. The smaller members of the family feed on vegetables and insects, but there are others which measure upwards of three feet across, and prey upon crocodiles' eggs, fish, and other water animals. II. BATRACHIA FROG-LIKE ANIMALS What does this word "batrachia" mean * Make the class tell, by referring them to their former lessons, A*j the kind of animals which form this group frogs, toads, and newts. The skin of these animals is always naked and moist ; why? Describe the use of the skin as a breathing organ, and the necessity for keeping it moist. How does the bony skeleton of the frog differ from that of most other animals ? It has no ribs. Let the class describe the way in which these animals bream by sucking in the air through the nostrils, and swallowing it in quips as we swallow our food. Lead up next to the curious life-history of the frog, making the class trace it from the egg to the matured animal Tell that because of this double sort of life these creatures have received the name of amphibious animals (amphis = both ; bios = life). III. FISHES Eefer to the former lesson on fishes, and make the class tell the characteristics of this group of vertebrates. They are pro- duced from eggs; they live entirely in the water; they breathe by means of gills, instead of lungs, all through life ; they have cold blood ; the heart has only two chambers; the body is covered with scales, and it is quite destitute of limbs. Lead them to tell the peculiar arrangement of the vertebra in these creatures. They are joined, not by pads of cartilage as in 254 OBJECT LESSONS STAND, iv mammals and birds, not by ball-and-socket joints as in snakes, but by hollow cups placed edge to edge, and filled with fluid. What is the advantage of this arrangement 1 Tell of the element in which they live, and that flexibility rather than strength is the one thing necessary. 1. Osseous and cartilaginous fishes. Tell that it is by the character of the skeleton that we are enabled to make our first classification of fishes. In most fishes the skeleton is made of a hard bony substance, as in the case of the other vertebrate animals. The scientific name for these is OSS60US fishes, because "osseous" means "bony." Others have no actual bones, but only gristle or cartilage to form their skeleton. These we call the cartilaginous fishes. Cartilage is another name for gristle. Sharks, rays, and sturgeons have gristly skeletons, and belong to this group. 2. Osseous fishes are grouped into two classes accord- ing to the nature of their fins. Show a fresh herring, and let the children examine its fins. Point out that they are soft and flexible to the touch. Lead the class to tell of other common fish which have similar soft, flexible fins. The sole, plaice, turbot, salmon, and eel belong to this group. We call them soft-finned fishes. Show next, if possible, a mackerel ; or, better still, a perch. Let the children examine it and run their fingers against the dorsal and ventral fins. Are these soft and flexible ? Can they be pushed aside with the finger ? No ; they are formed of sharp, bony spikes or spines. These spines give the name to fishes of this class. We call them spine-finned fishes. They form a much smaller group than the softrfinned fishes. LES. XLVI STRUCTURE AND HABITS COMPARED 255 Lesson XLVI STRUCTURE AND HABITS COMPARED I. GENERAL BUILD OF THE BODY LEAD the children to tell what they can of the build of their own bodies. The body consists of three distinct parts head, trunk, and limbs. Let them describe each part, as far as they can, in a general way. Show that the form of the body depends entirely upon the internal bony skeleton. It is upon this skeleton or framework that the body is built. It is this skeleton which holds the various parts of the body together, and gives it its characteristic shape. Lead the children to compare the general build of their own bodies with the plan of structure in various animals. Show that there is great similarity between the two, and that it is the bony skeleton which is modified in form to suit the requirements of the different animals. What is the essential part of the skeleton in man and in all vertebrate animals ? The backbone or vertebral column. It supports the head, it carries the ribs and limbs, it contains the spinal cord. Call upon the class to describe, as far as they can, the human spine, and compare it with the vertebral column of other animals a mammal, a fish, and a snake giving the reasons for the special modification in each case. What is the object of the pads of gristle between the vertebrae of a man 1 Why should these give place to ball-and-socket joints in the snake family ? What is the purpose of the double cup-joint between the vertebrae of the fish 1 We will now examine each of the three parts head, 256 OBJECT LESSONS STAND, iv trunk, and limbs, taking the human body as our model for comparison. II. THE HEAD The head consists of two parts, the skull and the face. The skull is simply a bony box in which the brain is lodged and protected. The skull rests upon the topmost of the vertebral bones ; and in the base of the skull is a round hole communicating with the spinal canal which runs through those bones. That extension of the brain, which is known as the spinal cord, passes out through this hole into the canal. In man the skull occupies by far the greater part of the head. Man is superior to all other creatures because he possesses a very great brain in comparison with his size. All the rest of the head, which is not part of the skull, forms the face. Pass a, tape round a boy's head, in a line with the eye- brows in front and to the nape of the neck behind. Explain that such a line would show the position of the skull or brain- case and the face. Compare the relative sizes. Explain, and show by familiar examples, that in the lower animals it is the face which is developed and not the brain-case. From the brain, nerves pass out through special holes in the skull to the organs of sight, smell, hearing, and taste. Lead the class to tell that many animals depend entirely upon their sense-organs, some for their daily existence, others for safety against their enemies. Show how nature specially develops these organs to suit the life and habits of the individual. On the one hand the large, powerful, piercing eyes of the night-prowling flesh-eaters, and on the other the large, erect ears of timid, defenceless animals, such as the deer and antelope, the horse, the rabbit, and the hare, will serve as illustrations of this special development. LES. XLVI STRUCTURE AND HABITS COMPARED 257 Those animals which rely to a large extent on their sense of smell are distinguished by their elongated faces, the nasal passages being specially developed to give greater scope for the nerves of smell. Name a few common examples. We shall deal with the mouth, teeth, and tongue in a later lesson. III. THE TRUNK Returning to the human body, lead the class to tell that the trurJ: is that part which would be left if head and limbs were lopped off. The trunk is built up on the framework of the verte- bral column and ribs. It contains all the vital organs of the body. The general plan of structure is very similar in all mammals. There is an upper division (the thorax), and a lower division (the abdomen) ; the two cavities being separated by a partition known as the diaphragm. The internal organs contained in these cavities will form the subject of a later lesson. IV. THE LIMBS Man has two pair of limbs, but although the general plan of structure is the same as in other mammals, man uses only the lower limbs for the purposes of locomotion. Compare the awkward stooping gait of the apes with the erect walk of man. Compare the short solid legs of the elephant, rhinoceros, and hippopotamus with the slender legs of the deer and the antelope family, and others ; and let the class explain the reasons for the special development in each case. Strength and solidity in one case ; speed in the other. In birds and in the flying mammals the fore limbs are built upon the same general plan as in mam- mals, except that the h&lld portion of the limb is lengthened out to form a wing for the purposes of locomotion in the air. Compare the bones of the human arm and hand with those of VOL. II s 258 OBJECT LESSONS STAND, iv tJie wing of a bird or a bat. Notice in the latter how the upper arm and fore arm are shortened, while the phalanges of the fingers are developed to an unusual size to form the frame- 'work of a wing, Snakes have no limbs ; but lizards and tortoises have the usual four limbs. Lead the class to tell the nature of the bony skeleton in the tortoise family. Explain that the bones of the limbs are not immovably fixed, like the rest of the skeleton, but are jointed and free to move. Show in the picture of the skeleton the sJwrt, thick bones of the limbs themselves, and the long, wide-spreading bones which form the hands and feet. The frog's mode of locomotion is by successive leaps. Show the disproportionate length of the hind limbs as compared with the fore. Explain the reason. The webbed feet fit this creature for swimming. Fish have no actual limbs. The pectoral fins take the place of the fore limbs ; and the ventral fins represent the hind limbs. It is the tail, however, that propels ; the fins are merely balancers. Lesson XLVII THE COVERING OF ANIMALS I. THE SKIN You know that the whole of the external surfaces of your body are covered with a thin coat or covering. We call it the skin. You know what a protection this thin covering is, because sometimes you have fallen down and grazed it, and the bare exposed place has been very sore. Thin as this skin is, it may be separated into two distinct layers. You have all seen the skin of the hand LES. XLVII THE COVERING OF ANIMALS 259 or the foot raised up in a blister. This raised blister is the upper layer of the skin separated from the lower one. Lead the class to tell that this outer layer is tough and horny and may be cut or pricked without causing pain. Run a fine needle through the outer layer on the thick part of the palm of the hand. It neither draws blood nor causes pain. Beneath this hard, tough, outer layer is another the true skin. The proper name of this under layer is dermis. The outer layer is called the epi-dermis, because it lies on the dermis. The under part of the dermis that next the flesh consists of fibres closely interwoven or matted together. The rest of the layer consists of soft little bags or cells, too small to be seen without the aid of the microscope. These cells are closely packed together, and are surrounded on all sides with nerves and blood-vessels. We could not prick the dermis anywhere with the finest needle without drawing blood and causing pain. Fresh dermic cells are being constantly formed from the blood, and as these form, they push the old ones up to the surface, where they become flattened into tough horny scales like the scales of a fish. These scales form the outer layer the epidermis. They are really dead flattened cells ; they are being con- stantly rubbed away off the surface of the body, and are also being constantly renewed from below. Eefer to the dampness of the skin, and say a few words about its work of cleansing the blood. Tell briefly of the sweat-glands and the pores; what the moisture is and whence it comes. The bodies of all animals which have an internal skeleton are covered with a double skin similar in structure to that of man. Eefer next to tJie lesson on fishes. Make the class tell the nature and arrangement of this coat of scales. 260 OBJECT LESSONS . STAND, iv Why scales in preference to hair, or feathers, or wool ? Take a fish (a Jierring] and scrape it before the class, to show the arrangement of the scales. They are all fixed in front, and overlap those behind. Remind them too of the slimy, oily fluid which exudes from under the scaly coat, and of the assistance it affords to the animal in making its way through the water. This scaly coat is the very best of coverings for such animals. But there are other animals which have a scaly coat as well as fishes. Snakes are covered with scales. Let the class tell the arrangement and purpose of these scales. They give the limbless creature a means of locomotion and climbing ; and by their arrangement they allow the body to distend, as it must do with the creature's peculiar habit of swallowing its prey whole. No other covering would do so well for these creatures as this coat of scales. Tell next of the frog and its moist, naked skin. Why this peculiarity ? Make the class describe the mode of breathing in these creatures, not only through the lungs but through the skin. The skin must be moist, however. Refer briefly to the tortoise family. Tell of their utterly defenceless state. The hard unyielding shell forms a protecting shelter into which the creature can withdraw himself on the approach of danger. This covering is made of the skin and the bones of the external skeleton all grown and welded together into a compact plate. II. COVERINGS FOR THE SKIN Show next that all the animals we have thus far enumerated have naked skins that is, they have no outer clothing or pro- tection other than the skin itself. In mammals and birds we find the skin clothed with a more or less thick and warm covering. LES. XLVII THE COVERING OF ANIMALS 261 In birds, this outer coat takes the form of feathers ; in most mammals the covering is hair. Refer to the lesson on birds, and make the class tell briefly the nature and form of a feather, and the special adaptability of such clothing for these creatures of the air, both for warmth, lightness, and as a means of locomotion. Most mammals, as we said, are clothed with hair. Let us think of some. The cat, the rabbit, and the squirrel have very smooth, soft coats. We call such a coat fur. But what is fur ? It is really fine, soft, silky hair, growing very close and thick on the skin. Take the sheep. It has a coat of wool. What is wool 1 It is only fine, long, curly hair, very close and thick on the skin. Lead the class to tell of animals, such as the horse, the cow, the goat, and others, whose bodies are covered with hair. Show the comparison. Think of the hog. What covering has his skin? Bristles. Well, what are bristles? Thick, strong, stiff hairs. Show that in some animals such as the hedgehog and porcu- pine these same stiff, strong hairs are found, only much stiffer and stronger still. We then call them spines. These outer coverings of feathers and hair (in its various forms) are all modifications of the same horny matter which forms the epidermis of the skin. It becomes in certain parts very hard and horny indeed, and forms nails on our hands and feet ; and claws and talons on the toes of various animals. The hoofs, horns, and antlers of other animals are all formed of the same hard, horny development of the epidermis of the skin. We use the skins of many of our large mammals to make leather. Make the class tell as many of these as possible, and after- wards add to the list such animals as the walrus, porpoise, seal, pig, hippopotamus, etc. Lead them to distinguish between hides and skins. Tell 262 OBJECT LESSONS STAND, iv that in tJie process of converting these skins and hides into leather, the whole of the epidermis is scraped away. It is only the under layer, i.e. the dermis, which is made into leather. Tell of the cetacea, which have naked skins, but spend their lives in the icy seas. They must have a warm covering. Wool, fur, or feathers would be out of the question. Describe the thick layer of fat or blubber underlying the skin, and tell how it keeps the body warm. Lesson XL VIII THE MOUTHS OF ANIMALS I. THE TEETH JUST as the limbs of animals are specially adapted to their mode of locomotion, so are the teeth, the form of the mouth, and even the movements of the jaw adapted to the kind of food the creatures eat. Lead the children to think of their own teeth. There was a time when we had no teeth ; we required none. We cannot recollect that time ; but we can all recollect the time when our first teeth came out, and others those we have now took their places. Infants begin to cut their milk teeth when they are about six months old. There are twenty in the complete set; they fall out when the child is about seven years old. We have more than twenty teeth in the permanent set. Lead the children to examine their own mouths and tell the number of teeth they find there. Let them begin with the eight chisel-shaped teeth in front, four in each jaw. Tell the name, incisors, and the meaning. Show the pur- pose of such teeth. How does a boy bite an apple ? Next point out the four long, sharp-pointed teeth on eitJier side of the incisors. LES. XLVIII THE MOUTHS OF ANIMALS 263 In the dog these teeth are very large indeed hence we call them canine (dog) teeth. Behind each of the canines is a row of broad, flattened teeth, with sharp points for grinding. We call them molars or grinders. In an adult's complete set there are five of these molars on each side of both upper and lower jaw twenty in all. Now that we know something of our own teeth, we shall find it easy to understand the peculiarities of struc- ture in the teeth of the various animals. 1. The Insectivora (insect-eaters). Refer to the earlier lessons, and make the children mention the mole, the shrew, the hedgehog, and the bat, as animals which live on insects. Show, if possible, the mouth of a mole. . Call attention to the teeth, bristling with sharp points, for crushing the hard, horny cases of beetles and other insects. They feed on insects, not by accident, but because their teeth are formed to crush such food. Some bats live on fruit. In these the molars have no sharp, cutting points, but are broad and rounded for the purpose of grinding. 2. The Carnivora (flesh-eaters). This is a very large and important order. It includes such land animals as the cats, dogs, bears, and weasels, as well as otJiers, such as the seals and whales, that live in the water. Show a picture of the open mouth of one of the great cats. Call attention to the enormous size of the four canine teeth, as compared with the small incisors between them. Tell the object of such teeth. They are intended to seize and hold the prey and to tear the flesh. Notice too the molars with their sharp, cutting edges, and describe the peculiar up-and-down movement of the jaw. Let the children move their own jaws, sideways as well as up and down, and they will see the difference. Cutting through the flesh-food, not grinding it, is the work which the cat's teeth have to do. Show a picture of the seal's teeth. 264 OBJECT LESSONS STAND, iv What is the seal's prey 1 Fish. Call attention to the peculiar modification in the teeth of this animal, to enable it to seize and hold fast its smooth, slippery prey. The teeth are furnished with sharp, saw-like edges, to serve the double purpose of holding and cutting. Tell of the peculiarity of the Greenland whale, which is entirely destitute of teeth. A, 1A*** Describe the transverse fringe of horny plates of whalebone which hang down from the roof of th-e mouth, and act the part of a trap or mesh in which to entangle the small creatures which alone the animal is able to swallow. Tell the mode of feeding. 3. The Rodents (gnawing animals). Show a picture of the mouth of a rabbit, a rat, or a squirrel. Let the children note the characteristic teeth of these creatures. There are no canines. Show the space on each side of the great incisors, where the canines should be, and the molars which follow. Refer to some of the earlier lessons, and let the children describe the peculiarity in the structure and growth of these chisel-teeth. Let them give the names of other members of this large order. 4. The Ruminants. Show a picture of the mouth of one of these animals, or, if possible, an actual sheep's head. What is the great peculiarity ? There are no incisors in the upper jaw. Lead the class to tell the object of the pad which takes the place of the incisors. Call attention to the molars all large, with broad crowns, specially adapted for grinding purposes. Tell of the double movement of the jaw, and why. 5- "^ ne toothless animals. Refer to the earlier lessons, ami make the class mention some of the members of this peculiar order. Some have no front teeth, others have no teeth at all. They live mostly on soft-bodied insects. Make the class describe the modifications that occur in the case of birds, fishes, and reptiles. Birds have no teeth. Their bills serve instead of teeth. I.KS. XLIX THE INTERNAL ORGANS 265 Fishes and reptiles have usually a large number ot small sharp teeth, all directed backwards. What is the object of this arrangement ? II. THE TONGUE 1. The Flesh-eaters. In the cat and dog families the tongue is long, fleshy, and very flexible. These animals drink by lapping with the tongue. Tell of the difference between the tongue of the cat and the dog. The cats' tongues are furnished with sharp, horny spikes or projections on the upper surface. With these spikes the animals clean the flesh from the bones, as with a rasp. The dog's tongue has no spikes ; it is smooth. 2. The Ruminants. These creatures have a long and very flexible tongue, which is of great use in gathering up the tufts of grass and pressing them against the pad in the upper jaw, while they are being torn off. 3. Many of the insect-feeding animals, both mammals and reptiles, have tongues specially adapted for securing their prey. The tongue is usually not only long and flexible, but is capable of being thrust for a considerable distance out of the mouth. As a, further aid in capturing their insect- food, the tongue is generally covered with a slimy, gummy fluid, which holds the victims fast while they are being conveyed to the mouth. Call upon the class to give examples of these. Lesson XLIX THE INTERNAL OEGANS I. THE BRAIN AND NERVOUS SYSTEM LEAD the class, by referring to some of the earlier lessons, to tell the chief characteristic of the vertebrate animals. 266 OBJECT LESSONS STAND, iv They all, man included, possess a vertebral column and a skull. Make them think of their own bodies, and tell that this vertebral column is not merely the central pillar of support, but that it forms also a long hollow tube, which contains the spinal cord. Let them next tell the nature of this spinal cord, and that it is continuous with the brain, which is itself lodged in the bony box of the skull. Tell briefly of the nature of the work which is done by this brain and spinal cord. Describe the delicate silver-white threads (the nerves) which pass out from them into all parts of the body. They are the message-carriers of the body. Some of these nerves spread themselves all over the muscles of the body ; and when we move, it is the brain which sends out its orders along the nerves, commanding the muscles to set to work. Others pass into the eyes, ears, nose, and tongue, and others again spread themselves all over the skin. These all carry messages up to the brain from those parts, and we are enabled to see, hear, smell, taste, and feel. The brain and nervous system are constructed on a very similar plan in all vertebrate animals, although thoy reach their highest perfection in man. Lead the children to think of man's intellectual superiority over all other creatures. Compare the weight of a man's brain (about 56 ounces) with that of a horse (19 ounces) or an elephant (150 ounces) in proportion to their sizes. Birds have smaller brains than mammals, and reptiles smaller still ; while fishes take the lowest place in this respect among the vertebrate animals. In the invertebrate animals there is no actual brain, and of course no spinal cord, because there is no spine. In most of these creatures there are small knobs or masses of nerve-matter from which delicate nerve- threads pass out. LES. XLIX THE INTERNAL ORGANS 267 II. THE HEART AND CIRCULATORY SYSTEM Tell next very briefly of the nature and purpose of the blood, and of its ceaseless flow into every part of the body. It carries nourishment to feed the worn-out tissues, and oxygen to burn up Ike waste, while its flowing stream carries away the poisonous products of the burning. The heart is the centre of all this movement. It is a force-pump, constantly at work pumping blood into all parts of the body. The blood is carried out from the heart by tubes called arteries. These branch out and break up into smaller and smaller vessels, until they become at last so small and fine that they are the merest hollow threads. These we call capillaries. The blood after passing through the capillaries is returned to the heart by other vessels called veins. III. THE RESPIRATORY ORGANS The blood which is carried back to the heart by the veins is laden Avith poisonous matters (chiefly carbonic acid). It is the business of the respiratory organs to get rid of these. What happens when we breathe into clear lime-water ? The water becomes white and milky-looking. This proves that carbonic acid comes off with our breath. Whence did this carbonic acid come? From the lungs. The lungs separated it out from the blood. But how did the blood get into the lungs ? Tell tlie nature of the heart, with its four chambers, two auricles, and two ventricles. The auricle and ventricle on one side are for the purpose of receiving the poison-laden blood from all parts of the body and sending it out again. But where does it go now? It is carried into the lungs. There, as we have seen, it gives off carbonic acid, which is breathed out through the mouth and nostrils. It 268 OBJECT LESSONS STAND. i\ at the same time takes in oxygen from the air, which we breathe into the lungs. The blood, freed from its poison-matters, and supplied with fresh oxygen, is sent back from the lungs to the heart ; but it goes to the other side of the heart now. The auricle on this side receives it from the lungs, and the ventricle pumps it out to all parts of the body again. Tell of the heat produced by the burning of the waste tissues. It is this which keeps our bodies warm. This is the general plan of the circulatory and respira- tory work not only in our own bodies, but in those of all mammals and in birds. The heart always contains four chambers, which are necessary for the complete purification of the blood in the lungs. The blood takes in much oxygen, in the lungs, and the bodies of all these animals are warm, because of the burning produced by this large amount of oxygen. In birds the lungs themselves are smaller than in mammals, but breathing goes on not only through these organs, but through all parts of the body, so that air penetrates everywhere. The hollow bones are filled with air, and there are air-cells in the cavity of the chest. Make the class tell the purpose of this arrangement. It is to render the body as light as possible. In reptiles the heart has only three chambers, instead of four ; and the lungs are small. Very little oxygen is taken in by these lungs ; consequently there is not sufficient burning to keep up a warm temperature, and the body is cold. The two upper chambers of the heart (auricles) open into a common ventricle. The ventricle has to receive the blood brought by the veins from all parts of the body as well as the purified blood sent back from the lungs. Instead, therefore, of sending out through the arteries pure blood, well supplied with oxygen, it sends out this mixture of the two. LES. XLIX THE INTERNAL ORGANS 269 Fishes differ from all other vertebrate animals in having gills instead of lungs. Refer to some of the earlier lessons, and make the class tell the nature and position of these peculiar organs, and whence they get the oxygen which is necessary to their work of blood- purifying. The heart has only two chambers, a single auricle and ventricle. The veins bring the blood to the auricle, and after passing into the ventricle it is then sent out through the gills, and thence into all parts of the body. A very small amount of oxygen is taken in from the water in this way ; consequently the oxidation or burning is not sufficient to warm the body. It is cold. We call these cold-blooded animals, as in the case of the reptile. STANDARD III LESSON I A BASIN ; two or three tumblers ; a saucer ; some water, milk, vinegar, coloured inks (or other liquids), turpentine ; solutions of salt or sugar. LESSON II Tumblers ; some coal, salt, small pebbles, water, glass-tubing, and lime-water. LESSON III The evaporating dish, tripod, and spirit-lamp (or Bunsen burner) ; a dry bottle, filled with fresh green leaves, and corked tight. LESSON IV A small kettle ; tumblers of warm and cold water. LESSON V Some pieces of ice ; a tumbler ; a basin of water ; some butter ; the iron spoon ; spirit-lamp ; a piece of lead, a cork, and a stone. 272 OBJECT LESSONS LESSON VI Some mercury ; a small saucer ; a test-tube and holder ; the spirit-lamp. LESSON VII Some mercury ; some vermilion powder ; a piece of looking- glass. LESSON VIII Some spirits of wine ; a piece of camphor ; a glass of water ; an egg. LESSON IX A large tumbler ; some warm water, molasses, yeast, malt, methylated spirit. LESSON X A glass flask ; a large basin or bowl of water ; a piece of glass-tubing ; an inflated bladder ; a syringe. LESSON XI The air-pump ; a test-tube filled with coloured water ; a large bowl of water ; a tumbler ; a sheet of writing-paper ; a boy's leather sucker. LESSON XII A pair of bellows ; a flask fitted with a funnel and a delivery tube ; a bottle or gas jar for collect- ing the gas ; some pieces of chalk or marble ; a taper ; hydrochloric acid. LESSON XIII A well-corked soda-water bottle filled with a mixture of coal-gas and air ; a picture of the Davy lamp (or an actual lamp if possible) ; a piece of Pio. i. wire gauze ; a taper. OBJECTS AND ILLUSTRATIONS REQUIRED 273 LESSON XIV A long clay tobacco-pipe; the Bunsen burner; some powdered coal ; a piece of soft clay ; a test-tube ; a bowl of water ; a cork. LESSON XV Some coal-tar and turpentine ; a piece of tallow ; a tumbler of water. LESSON XVI Some solid paraffin and paraffin oil ; a paraffin candle ; some benzoline ; a benzoline lamp ; a tumbler of water ; a saucer ; a email paraffin lamp. LESSON XVII A flask fitted with a funnel and a delivery tube ; two or three bottles for collecting the gas ; some pieces of chalk or marble ; some hydrochloric acid ; lime-water ; a taper ; a clean glass bottle with narrow neck ; a piece of glass-tubing. LESSON XVIII A saucer of lime-water ; some cress growing on flannel. See instructions. LESSON XIX A scarlet bean growing in a flower-pot. LESSON XX A growing scarlet bean, as in last lesson ; specimens or pictures of climbing, twining, prostrate, and creeping stems. LESSON XXI Some wall-flowers ; some seed-pods of the same. VOL. II T 274 OBJECT LESSONS LESSON XXII A few common flowers. LESSON XXIII Some well-soaked seeds of the scarlet bean, or Windsor bean ; a few peas, acorns, almonds, plum and cherry stones ; apple- pips. LESSON XXIV Some bean-seeds in pots in various stages of growth. See instructions. LESSON XXV Some grains of wheat and Indian corn ; a few grains of Indian corn that have been soaking in water for some days ; a sharp knife ; a well-soaked bean-seed ; some common grass seed. LESSON XXVI A picture of a tree ; a piece of the woody stem of a tree with the bark ; a cabbage-stalk ; a specimen of oak-stem with thick bark ; some twigs of lime-tree ; some common bast. LESSON XXVII A picture of the growing flax-plant ; an actual flax-stalk, if possible ; some linseed ; a piece of linen ; some raw hemp and jute fibres ; specimens of rope, cordage, and canvas. LESSON XXVIII A picture of the growing flax-plant ; a cabbage-stalk. OBJECTS AND ILLUSTRATIONS REQUIRED 275 LESSON XXIX A stick of scutched flax fibres ; a bundle of heckled line ; specimens of fine linen, diaper, duck huckaback, sheeting, damask ; black-board sketch showing the arrangement of warp and woof ; a shuttle ; picture of a hand-loom. LESSON XXX A sketch showing old birds feeding their young ; a bird of ne sort (either alive or a stuffed specimen). FIG. 3. 276 OBJECT LESSONS LKSSON XXXI A few quill feathers ; a sharp knife ; some goose quills ; a quill pen ; some quill nibs. LESSON XXXII A picture of the bony skeleton of a bird ; an actual bird of some sort, as in Lesson XXX. *, a sketch showing the huads of various birds ; a similar sketch showing the feet of birds. ..-. - . Fro. 4. OBJECTS AND ILLUSTRATIONS REQUIRED 277 FIG. 5. THRUSH. FIG. 6. PARROT. FIG. 7. EAGLE. 7iG. 9. DUCK. 278 OBJECT LESSONS Fir.. 14. WADER. tlO. 15. SWIMMEH. FjO. 1C. lU'.NSKK. OBJECTS AND ILLUSTRATIONS REQUIRED 279 LESSON XXXIII Pictures of an eagle, stork, woodpecker, parrot, and crow ; a piece of worm-eaten wood ; a duck's head. LESSON XXXIV Sketch of the feet of birds, as in Lesson XXXII. ; the foot of a fowl ; pictures of a stork and an ostrich ; a duck's foot. LESSON XXXV A picture of the common snake ; picture also of the bony Fir,. 17. 280 OBJECT LESSONS skeleton of the same ; a wooden model of a ball-and-socket joint LESSON XXXVI Pictures of the viper and rattlesnake, the common English snake, and the boa-constrictor and python. LESSON XXXVII Picture of a frog ; a living specimen ; a bowl of water ; skeleton of a frog (or a picture of one). Fid. 18. XXXVIII Skeleton of a frog ; living specimens of a frog and a toad (or, failing them, a picture). OBJECTS AND ILLUSTRATIONS REQUIRED LESSON XXXIX Some tadpoles in a bowl of water, if possible-if not a picture ; a fresh herring or a mackerel ; picture showing the tadpole in various stages of development. i-'lG. 10. 282 OBJECT LESSONS Fio. 20. LESSON XL A herring or mackerel (or some other common fish) ; a living fish in a bowl of water ; a smooth pointed piece of wood. A small, smooth, wooden wedge ; the backbone of a herring or a mackerel ; a fish in a bowl of water ; a herring with a hard roe. LESSON XLII A picture of a bee, common house-fly, butterfly, moth, beetle, grasshopper, and ant ; dead specimens of each pinned to a sheet of cardboard ; a few caterpillars. OBJECTS AND ILLUSTRATIONS REQUIRED LESSON XLIII A silkworm's cocoon ; some leaves from the garden with pupa forms gummed to their under surface. (There is generally 110 difficulty in finding these in the garden in summer time.) LESSON XLIV A picture of a spider, and one or two dead specimens ; a sketch of the spider's claws. FIG. 21. LESSON XLV A sketch on black-board of the spider's web. FIG. 22. 284 OBJECT LESSONS STANDARD IV LESSON I A hammer, nutmeg-grater, spirit-lamp ; test-tubes ; a tumbler ; a bowl of water ; a spoon ; a lump of sugar ; some salt, mercury ; piece of chamois leather ; bar of iron ; a brick ; pieces of lead, wood, glass, and chalk ; a leaden bullet ; a piece of india-rubber. LESSON II A piece of chalk ; a saucer ; some coloured water ; a tumbler ; a piece of cane ; some paraffin ; set of glass capillary tubes. LESSON III A hammer ; pieces of chalk, lump-sugar, brick, wood, stone, lead, cane, cork, whalebone, copper and iron wire ; stick of slate-pencil ; a strip of glass ; some gold - leaf, lead and tin foil, and sheet-iron ; a hammer and a flat iron ; thin glass rod or tubing ; the Bunsen burner. LESSON IV Pieces of cork, wood, stone, and lead, of equal size ; a bag of feathers ; a jug of water and a tumbler ; a globe ; sketch on black-board. LESSON V Two or three tumblers ; a basin, jug, and bottle ; some peas, shot, or small round seeds ; water, treacle, flour, saw-dust ; a (J tube ; a watering-can ; a spirit-level ; a syringe ; a corked bottle. OBJECTS AND ILLUSTRATIONS REQUIRED 285 LESSON VI A " tin " box (a biscuit-tin would do well) ; some bricks ; a can of water ; a broad flat piece of some light wood ; a glass cylinder and a piece of bladder ; a light disc (which might easily be made out of the lid of a round " tin " canister) ; a large bowl of water ; a hollow india-rubber ball. LESSON VII A long round cardboard case, closed with a bung or cork at one end ; the glass cylinder and disc of last lesson ; a gimlet and a few wooden plugs. LESSON VIII A block of flint-glass, weighing about 3 ounces ; a large basin of water ; a pair of scales and weights ; pieces of brick and sulphur about the same size as the glass ; pieces of cork, oak, beech, white pine; an inflated bladder; a "tin" box or canister, with a hole bored in one of its sides ; pieces of iron and tin. LESSON IX A boy's leather sucker ; a brad-awl ; a tumbler ; a large basin or bowl of water ; a thin card or a sheet of writing-paper. LESSON X A large test-tube ; a bowl of water ; a small test-tube ; some mercury and a small bowl ; a glass tube, of small bore and about a yard in length. LESSON XI A pair of scales ; the long tube, mercury, and bowl of 286 OBJECT LESSONS the last lesson ; sketch on black-board of the dial of a barometer. Fiu. -J3. LESSON XII A glass tube open at both ends ; a bowl of water ; a small bottle filled with water, and fitted with a cork, through which a piece of glass tube is passed ; a syringe or a ' common squirt ; a little coloured water. LESSON XIII Picture of a well ; sketch of the pump on the black-board ; a pair of bellows ; a small glass model of a puni]>. OBJECTS AND ILLUSTRATIONS REQUIRED 287 288 OBJECT LESSONS LESSON XIV Black-board sketches of the lifting-pump, the force-pump, and the fire-engine. OBJECTS AND ILLUSTRATIONS REQUIRED 289 LESSON XV Black-board sketch of the air-pump ; an actual air-pump if possible. LESSON XVI The spirit-lamp ; a piece of iron ; small tongs ; bowl of cold water ; some ice ; a short round bar of iron, fitting into a groove and ring ; a brass ball suspended by a chain, and a ring through which it will just pass ; a kettle of boiling water ; some test- tubes and holders ; mercury ; coloured water ; a corked flask, with a long glass tube fitted into the cork ; a glass retort. LESSON XVII A piece of iron ; some ice, butter, bees'-wax, camphor ; a spoon ; the spirit-lamp. LESSON XVIII Three basins ; some ice ; hot and cold water ; the flask filled with coloured water which was used in Lesson XVI. LESSON XIX A thermometer ; some pieces of capillary glass tubing. LESSON XX A large basin ; some ice ; a small kettle ; Bunsen burner. LESSON XXI The flask and tube of coloured water, as used in Lesson XVI. ; a kettle ; the Bunsen burner ; a large basin ; some cold water ; some ice. LESSON XXII Pieces of oak-stem, cane, and bamboo, LESSON XXIII The piece of oak-stem ; a small branch from some growing tree willow for preference. VOL. II U 260 OBJECT LESSONS LESSON XXIV Some acorns and pine-cones ; pieces of oak and fir stems ; a few oak leaves and pine leaves. LESSON XXV Specimens of the following woods: ebony, lignum vitac, Spanish mahogany, yellow pine, larch, poplar ; a basin of water. LESSON XXVI Specimens of all the woods mentioned in the lesson, or of as many as possible ; and pictures of the various trees. LESSON XXVII The apparatus for separating nitrogen from the air, and pre- paring oxygen from potassium chlorate, as described in the lesson ; a taper ; some splinters of wood, charcoal, phosphorus, sulphur ; the deflagrating spoon. LESSON XXVIII One or two jars of oxygen prepared beforehand ; a piece of charcoal ; some lime-water ; a taper. LESSON XXIX The apparatus for generating hydrogen, as described in the lesson ; some test-tubes ; a taper. LESSON XXX A wall-sheet picture of the human skeleton ; also pictures of the skeletons of a horse, a rabbit, or a bird. LESSON XXXI One or two long bones, showing the condyles with their smooth, curtilage covering ; the chart of the skeleton as in the last lesson. OBJECTS AND ILLUSTRATIONS REQUIRED LESSON- XXXII Two smooth strips of wood joined together at one end by a peg which leaves them free to move, with a piece of rope jom- in" the two opposite ends ; a sheep's brain. FIG. 23. LESSON XXXIII A hollow india-rubber ball ; a diagram black-board sketch of the heart in section. Fio. 29. 292 OBJECT LESSONS LESSON XXXIV A wall-sheet or black-board sketch of the alimentary canal. LESSON XXXV Diagram of the heart, as in Lesson XXXIII. ; sheep's lights. LESSON XXXVI Some wooden reels strung on a cord ; some vertebral bones, either of the sheep or the rabbit. LESSON XXXVII The vertebral bones used in the preceding lesson. LESSON XXXVIII Pictures of the classes of animals referred to in the lesson. LESSON XXXIX Pictures of the invertebrate animals named ; the grub and pupa forms. LESSON XL A snail and a slug ; a whelk, periwinkle, and cowrie shell ; a mussel and an oyster ; a scallop and cockle ; a dried star-fish ; and a picture showing some of the living creatures. OBJECTS AND ILLUSTRATIONS REQUIRED 293 LESSON XLI Pictures of apes, baboons, and monkeys ; the bat, with a good sketch of the hand-wing ; the mole, hedgehog, and shrew. LESSON XLII Pictures of as many as possible of the animals named in the lesson. LESSON XLIII Pictures of the eagle and the owl ; the parrot and wood- pecker ; the sparrow, thrush, or blackbird ; fowls and partridges. LESSON XLIV Pictures of the various orders of birds named in the lesson. LESSON XLV Pictures of snakes, lizards, frogs, and tortoises ; a tortoise- shell, or if it can be obtained, a living tortoise ; a fresh herring, a mackerel, or a perch. 294 OBJECT LESSONS LESSON XLVI Black-board sketch of the wing of a bat, as in Lesson XLI. ; pictures of the skeleton of the tortoise and the frog. LESSON XLVI I A fresh fish of some sort (a herring for preference). LESSON XLVIII A sketch showing the arrangement of the human teeth ; the stuffed specimen of the mole which was used in the earlier lessons ; a picture of the head of one of the great cats, with the mouth open to show the teeth ; the teeth of the seal and the rabbit, the cow or the sheep. Fio. 31. CAT'S HEAD. Fia. 32. SEAL. Fiu. 33. RABBIT. OBJECTS AND ILLUSTRATIONS REQUIRED 295 FIG. 34. Cow. LESSON XLIX Sketch showing the human brain and spinal cord in section. END OF VOL. II Printed by R. & R. CLARK, LIMITED, Edinburgh.