Chapter 24

FORM III

WINTER

CARE OF PLANTS IN THE HOME

The care of flowering bulbs which was begun in Form I will be continued in Form II. The growing of new plants from cuttings will now be taken up. In those schools which are kept continuously heated, potted plants may be kept throughout the year. The pupils will come to appreciate the plant's needs and learn how to meet them in the supply of good soil, water, and sunlight. The following points should be observed:

1. Good potting soil can be made by building up alternating layers of sods and stable manure and allowing this compost to stand until thoroughly rotted. A little sharp sand mixed with this forms an excellent soil for most house plants.

2. Thorough watering twice a week is better than adding a little water every day.

3. The leaves should be showered with water once a week to cleanse them from dust.

4. An ounce of whale-oil soap dissolved in a quart of water may be used to destroy plant-lice. Common soap-suds may also be used for this purpose, but care should be taken to rinse the plants in clean water after using a soap wash.

5. Most plants need some direct sunlight every day if possible, although most of the ferns grow without it.

6. Plants usually need re-potting once a year. Many kinds may be set out-of-doors in flower beds in May and left until September, when they may be taken up and placed in pots, or cuttings made from them for potting.

7. A flower exhibition at the school once or twice a year, or at a local exhibition, adds to the interest.

8. The pupils should report to the teacher from time to time the progress of their plants and make many drawings showing their development.

PLANT CUTTINGS

The pupils will be interested to know that it is possible to produce new plants without waiting for them to grow up from the seed. It will indeed be quite a surprise to them to see a new plant complete in all its parts grow up from a small piece of stem, root, or even leaf. With a little care even children may propagate plants in this way.

SELECTION OF CUTTINGS

Begin with some of the common herbaceous bedding-plants, such as geranium, coleus, or fuschia. These are such common bedding-plants that they are easily obtained in the autumn. Only well-matured stems of the season's growth, such as will break with a slight snap when bent, should be used.

Let the pupils provide themselves with sharp knives for the lesson, with small boxes or pots, and with some moist, clean sand--not potting soil. A few holes should be bored in the bottom of the box, then a layer of fine gravel put in to provide for good drainage, and over it layers of moist sand. Take a slip or growing end of a stem about three inches in length, always cutting it at or just below a node, or joint, and leaving only a couple of small leaves on the top of the slip. Insert it to about half its depth in the box of moist sand. These cuttings may be placed a few inches apart in the box, which should then be placed in a warm, light room for a few weeks until the roots develop. The cuttings should be partly shaded by papers from the strong sunlight, and the sand kept slightly moist but not wet. Bottom heat and a moist, warm atmosphere hasten their development.

Another very convenient and very successful method of starting cuttings is to take a six-inch flower-pot, put two inches of fine gravel in the bottom, set a four-inch unglazed flower-pot in the centre, and fill up the space around it with sand and garden-loam, mixed. Put a cork in the hole in the bottom of the small flower-pot, and then fill it with water. Put the cuttings around in the space between the two pots and set in a fairly warm room in moderate light.

POTTING OF ROOTED CUTTINGS

When the cuttings are well rooted, which requires from three to six weeks according to the variety and growth conditions furnished, they should be carefully lifted with a trowel and each set in a small pot or can. First put in the bottom a few small stones to secure drainage, and then a little good potting soil. Set the plant in place and fill in around with more soil and pack this firmly around the roots. Keep room in the top of the pot for water. When the new plant has made some growth, it may be shifted to a larger pot. Geraniums and coleus (foliage plants) should not be kept more than two seasons. Take cuttings off the old plants and then throw the latter away.

EVERGREENS

In December make a study of Canadian evergreens, choosing spruce, balsam, and cedar, if available, or substitute hemlock for any one of these.

Compare the general features of these trees, such as shape, direction of branches, colour, persistence of leaves through the winter.

Have the pupils notice how nature fits these trees to endure the snows and storms of winter by:

1. The tapering cone which causes the snow to slide off the tree.

2. The fine, needle-shaped leaves to which only very sticky snow will adhere.

3. The very tough, flexible, and elastic branches, which bend in the wind and under the weight of snow, but spring back to their old positions.

4. The resin in leaves, stems, and buds, which enables the trees to resist frost and rain.

Teach the pupils to distinguish these trees by their differences in colour and form and also by the differences in their leaves and cones.

CLASS-ROOM LESSON

Distribute small twigs of balsam and require the pupils to observe and describe the length, shape, and colour of the leaves.

Next distribute small twigs of spruce and require the pupils to compare the spruce leaves with those of the balsam in length, shape, and colour.

Next distribute twigs of cedar and proceed similarly.

The cones may be dealt with in a similar manner. Require the pupils to make a census of the evergreens of the locality, recording the class of evergreen, the size, and the use of each kind for shade, ornament, or for commercial purposes.

_To the teacher._--The balsam, spruce, and hemlock are difficult for the beginner to distinguish, but this may be done by noting the following points of difference in their leaves:

The leaf of the hemlock is the only one that has a distinct leaf-stalk. Look for this tiny stalk.

The leaf of the hemlock, like that of the balsam, is flat, but the hemlock leaf is much the shorter.

The leaf of the spruce is not flat, but is three-sided or nearly so. Its colour is uniform, while the under surface of the hemlock leaf, and also of the balsam leaf, is of a decidedly lighter colour than the upper surface.

Note that the spruce _type_ is studied; no attempt is made at this stage to differentiate the several species of spruce.

COLLECTION OF WOOD SPECIMENS

During the winter months the boys may prepare specimens of wood for the school collection. These specimens should be cut when green, and dried afterwards. They should be uniform in length--not more than six inches--and should show the bark on one side. The side showing the bark should be two inches wide at most, six inches long, and running in a V-shaped, radial section toward the pith. A tangential section also shows well the rounded layers. A piece of slab as cut lengthwise off a round stick is tangential. Care should be taken not to mutilate trees in taking these specimens. Specimens of rare or foreign woods may be obtained at wood-working factories.

RELATED READING

Winter is Nature's quiescent period. Continuous active observation in the out-of-doors among the plants of the forest and garden gives place for a time to indoor work and reflection. Pupils need time for reading and reflection, and no time is so opportune as the quiet winter season. During these months some time should be devoted to the reading of nature stories and extracts from magazines and books dealing with plant as well as with animal life.

Pupils should review their gardening experiences and discuss plans of improvement for the approaching spring and summer. Let them write letters to the Form II pupils of other schools where similar work has been carried on, and give some of their experiences in gardening and other plant studies, and also in animal studies. A certain Friday afternoon might be appointed for hearing the letters read which were received in reply. Suitable short poems that have a direct bearing upon the outdoor studies should be read from time to time. Good pictures also come in here as an aid in helping the pupils to appreciate written descriptions. The first-hand observations made by them will form a basis for the better and more appreciative interpretation of these literature selections.

For Observation Lesson on Weed Seeds, see page 171.

HOW ANIMALS PREPARE FOR WINTER

~Introduction.~--Discuss the preparations that people make for winter, such as the storing of food and the providing of warmer clothes and homes.

~Method.~--The teacher questions the pupils and encourages them to tell what they have learned through their own observation of animals. The knowledge of the pupils is supplemented by information given by the teacher, but the pupils are left to find out more facts by further observations. Thus:

Do you ever see ground-hogs out during winter?

What do they feed upon during the winter?

What is the condition of ground-hogs in late summer and in autumn?

What is the use of the great store of fat that they have in their bodies?

Examine the snow near the burrows of ground-hogs and find whether they ever come out in mid-winter.

_To the teacher._--The hibernating animals prepare a home or nest and lay up a store of food in the form of fat within their bodies. To hibernate does not mean the same as to sleep. The hibernating animals have much less active organs than the sleeping animals. The heart-beat and the respiratory movements are very slow and feeble, consequently a very little nourishment suffices to sustain life.

SUMMARY OF LESSONS

(Two lessons of twenty minutes)

1. Some animals migrate:

Examples--many birds, butterflies, and some bats; the cariboo, and buffalo.

2. Some animals hibernate:

Examples--bear, ground-hog, raccoon, frogs, toads, snakes, and some bats.

NOTE.--Flies, mosquitoes, and some other insects crawl into crevices and remain at rest during winter, but their bodies are not stored with food.

3. Some animals build houses and store foods:

Examples--beaver, squirrel, chipmunk, honey-bee, deer-mouse.

4. Some animals build homes convenient to food:

Examples--musk-rat, field-mouse.

5. Some animals put on warmer clothing:

Examples--fox, mink, otter, rabbit, horse, cow, partridge, chickadee. The rabbit and weasel turn white, a colour protection.

6. Many insect larvae form cocoons or pupae cases:

Examples--emperor-moth, codling moth, tomato worm.

CORRELATIONS

With literature, reading, and language.

With geography: By a lesson on "The influence of climate upon animal and plant life."

CHICKENS

(Consult _Principles and Practice of Poultry Culture_ by Robinson. Ginn & Co., $2.00.)

CONVERSATION LESSON

How many of you keep chickens at your homes?

Why do many kinds of people keep chickens?

What breeds of chickens do you keep?

How many other breeds do you know?

Describe the appearance of a few of the commoner breeds.

Why are there so many different breeds?

Name those that are good laying breeds.

Name breeds that are not usually considered good laying breeds.

_To the teacher._--Chickens are kept by all classes of people. Many keep them for the profit in eggs and meat, others keep them as a fad, and others to gratify a craving for animal companionship. There are one hundred and seventy-five recognized breeds, varying in size from that of the Japanese bantam weighing ten ounces to that of the huge Brahma which weighs fourteen pounds. The shapes and colours present as great a variation as the sizes. The breeds that are usually regarded as good layers are White Leghorn, Barred Bock, and Rhode Island Red, while the Game breeds are usually regarded as poor layers. Careful tests prove, however, that there are good laying and poor laying strains in every breed, and care must be taken to select from good strains, since the breed is not a sufficient guide.

At the close of the first lesson, assign to the pupils the task of making a chicken census of the district as follows:

1. Request each pupil to count the number of hens under two years old at his home and also to count the hens that are more than two years old.

2. Request each pupil to find out, if possible, the number of eggs obtained at his home during the whole year.

ARITHMETIC LESSON BASED ON THE CHICKEN CENSUS

1. Using the data collected by the pupils, calculate the total number of chickens under two years old in the district.

Calculate the number over two years old. (The latter are classed as unprofitable.)

2. Using the data obtained by the pupils (provided sufficient data was obtained to make it reasonably reliable), calculate the average number of eggs laid a year by each hen.

3. If the data collected by the pupils as to the number of eggs is thought to be unreliable, make use of the following:

The average number of eggs laid each year by each hen in Ontario is seven dozen. Use this average number, and:

(1) Calculate the value of the eggs produced in this district in a year, the average price of eggs being twenty cents a dozen.

(2) If the average production of eggs were increased to ten dozen (a number that is easily possible under improved management), find the value of the eggs that would be produced in a year, and find the gain that would result from this better management.

4. If it costs ninety cents a year to feed a hen, find the net annual profit to this district from the egg production.

CARE OF CHICKENS

The method of developing conceptions of how to take proper care of chickens is based partly upon the pupils' experiences and partly upon a knowledge of the history of the original wild hens.

Information can be gathered from the pupils as to the date of hatching of the earliest chickens and the date at which the pullets begin to lay. Chickens that are hatched in April begin to lay in November or December and lay throughout the winter when eggs bring the highest price.

The original wild hens lived in the dry, grassy, and shrubby jungles of India. They were free to move about in the open air, and at night they perched in the trees, which sheltered them from rain. Hence may be inferred what kind of quarters should be provided for chickens.

CARE AND FOOD OF CHICKENS

Points developed

Chickens must have plenty of fresh air without draughts.

Heat is not necessary.

Their quarters must be dry, clean, and well lighted.

They require exercise.

Their food must have in it the materials that are needed to make the substance of the egg.

Breakfast: Wheat or corn scattered among straw--the scratching affords exercise.

Dinner: Meat scraps, slaughter-house refuse, vegetables, sour milk, and rolled oats.

Supper: As at breakfast.

PHYSICAL SCIENCE PHASE OF NATURE STUDY

The teacher is advised to read carefully the instructions and General Method of Experimental Science, Chapter I, before beginning the lessons in Physical Science.

SOLIDS, LIQUIDS, AND GASES

Arrange a collection of objects of various shapes, sizes, colours, and weights, as cork, glass, lead, iron, copper, stone, coal, chalk. Show that these are alike in one respect, namely, that they have a shape not easily changed, that is, they are _solids_. Compare these solids with such substances as water, alcohol, oil, molasses, mercury, milk, tar, honey, glycerine, gasolene. These latter will pour, and depend for their shape on the containing vessel. They are _liquids_. Compare air with solids and liquids. Such a material as air is called a _gas_. Other examples of illuminating gas, and dentists' "gas"; others will be studied in future lessons. Pupils may think all gases are invisible. To show that some are not, put a few pieces of copper in a test-tube or tumbler and add a little nitric acid. Watch the brown gas fall through the air; note how it spreads in all directions. Some gases fall because they are heavier than air; others rise because lighter. All gases spread out as soon as liberated and try to fill all the available space. Spill a little ammonia and note how soon the odour of the gas is smelled in all parts of the room.

CHANGE OF STATE

Heat some lead or solder in a spoon till liquid. Let it cool. Do the same with wax.

Heat some water in a flask till it becomes steam. Steam is a gas. Cool the steam and form water again. (See distillation.) Refer to lava (melted rock), moulding iron, melting ice and snow, softening of butter.

All solids may be changed to liquids and even to gases if sufficiently heated. Likewise all gases may be changed into liquids and then to solids.

EXPANSION OF SOLIDS

In winter pupils may find that the ink is frozen. The teacher directs attention to this and inquires why it has occurred. It may be that in a lesson on rocks the teacher will ask the pupils to account for all the little stones. The following _experiments_ will aim at solving the foregoing problems:

1. A brass ball and ring are shown. Pupils handle these and note that both are cold and that the ball just passes through the ring. They are asked to compare the size of the ball with that of the ring.

2. The spirit-lamp is lighted and examined. Pupils hold their hands over the flame to note the heat.

3. The ball is heated in the flame for a short time by one of the pupils, and felt cautiously. An attempt is made to pass it through the ring. How has the ball changed in feeling? In size? How does one know it is larger? What has caused these changes?

4. Cool the ball. Feel it. Try to pass it through the ring now. How has it changed in feeling? In size? What caused these changes? How does heat affect the ball? How does cold affect it?

The teacher may now give the words _expand_ and _contract_, writing them on the black-board and explaining their use. Pupils may then state their conclusions: _A brass ball expands when heated and contracts when cooled._

A blacksmith can make the following very serviceable apparatus: A scrap of iron about eleven inches long, one inch wide, and one-eighth inch thick, has one inch bent up at each end. A rod one-eighth inch in diameter is made just long enough to pass between the upturned ends of the first piece when both are cold. The rod is heated and the experiment conducted as in the case of the ball. Two additional facts are learned: (1) Iron expands as well as brass; (2) solids expand in length as well as in volume. The pupils may now be told that other solids have been tried and expansion has invariably followed heating. The conclusion may then be made general.

PRACTICAL APPLICATIONS

1. When your ink-bottle was placed on the stove, which end became warmer? Which expanded the more. Why then did it crack?

2. What other examples like this have you noticed? (Lamp chimneys, fruit jars, stove plates)

3. The earth was once very hot and is now cooling. How is the size of the earth changing? Does it ever crack? What causes earthquakes?

4. Find out by observation how a blacksmith sets tires.

5. Invent a way to loosen a glass stopper stuck in the neck of a bottle.

6. What does your mother do if the metal rim refuses to come off the fruit jar?

7. Next time you cross a railway, notice whether the ends of the rails touch. Explain.

8. What allowance is made for contraction in a wire fence? A railway bridge? Why?

9. Why do the stove-pipes crack when the fire is first started?

10. Why does the house go "thump" on a very cold night?

11. Draw the ball, ring, and spirit-lamp in position.

12. Describe in writing the experiments we have made.

QUESTIONS FOR FURTHER INVESTIGATION

You have seen that iron and brass both expand. Do they expand equally? Let pupils have a few days to invent a way of answering the question. The experiment may then be tried with the compound bar. See _The Ontario High School Physics_, pages 217-218, also _First Course in Physics_, Milliken and Gale, page 144.

If the equipment of the school is limited, it may be necessary to dispense with the ball and ring and generalize from one experiment.

Another easily made apparatus consists of two iron rings with handles. One ring will just pass through the other when both are cold. The stove may take the place of the spirit-lamp.

A still simpler plan consists in driving two nails into a block at such a distance apart that an iron rod (six-inch nail, poker, bolt, etc.) will just pass between. On heating the rod the increase in length becomes evident.

EXPANSION OF LIQUIDS

Fill a common bottle with coloured water; insert a rubber stopper through which passes a glass tube about sixteen inches long. Set the bottle in a pan of water and gradually warm the water. The rise of the liquid in the tube will indicate expansion. On setting the bottle in cold water the fall of the column of coloured water shows contraction. See _The Ontario High School Physics_, page 218, also _Science of Common Life_, page 48. Macmillan Co., 60 cents.

Set the flask or bottle in a mixture of ice and salt and note that the extreme cold causes contraction for a while, then expansion. Note that when expansion begins, the water has not begun to freeze, but that it does so soon after.

The night before this experiment the children should set out in the cold air, tightly corked bottles of water. In the morning they will be found burst by the expansion.

APPLICATIONS

1. Why did some of the ink-bottles burst in the cold room?

2. Find large stones split up into two or more fragments. Explain.

3. Why is fall-ploughed land so mellow in spring?

4. Why does ice float? Think what would happen if it did not.

5. Explain the heaving of oats, clover, wheat.

6. Do all liquids expand on freezing? Try melted paraffin.

THE THERMOMETER

Besides the ordinary thermometer the school should possess a chemical thermometer graduated from 0 deg. Fahrenheit to 212 deg.

1. Our sensations vary so much under different circumstances and in different individuals that they cannot be depended on. Find examples of this and show the need of a measuring instrument.

2. The pupils can learn, by examination of the common wall instrument, the parts of the thermometer--tube, bulb, liquid (alcohol or mercury), and scale.

3. Repeat the experiment for expansion of liquids, showing wherein the apparatus resembles the thermometer, warm the thermometer bulb and watch the column rise; cool it and note the fall.

4. Set the bulb of the chemical thermometer in boiling water. The mercury comes to rest near 212 deg. Bury the bulb in melting snow and notice that the column falls to 32 deg. Give names for these points. Explain that a degree is one of the 180 equal parts which lie between boiling point and freezing-point. Show that 32 deg. below freezing must be 0 deg., or zero.

5. The uses of thermometers for indoors and outdoors; for dairy, sick room, incubator, and soils; maximum and minimum. Dairy thermometers registering 212 deg. Fahrenheit may be obtained; they are cheaper than chemical thermometers.

EXPANSION OF AIR

Half fill a flask with water and invert it uncorked over water in a plate. Apply a cloth soaked in boiling water to the part that contains air. Why does the water leave the flask? Apply cold water. Why does the water return? Any ordinary bottle may be used in place of the flask, but it is more liable to crack.

Make an air thermometer. See _The Ontario High School Physics_, page 223, also _Science of Common Life_, page 41. Try to graduate it from the mercurial thermometer. Have the boys make a stand for it.

_Inferences._--Heated gases rise because they expand. Hot-air balloons, winds, and heating with hot-air furnaces, all depend on this principle.

SOURCES OF HEAT AND LIGHT

NOTES FOR A SERIES OF LESSONS

1. THE SUN.--Our dependence on it. Valuable results of its heat. Simple notions as to its size, distance, and nature. Our earth catches a very small fraction of the sun's heat; our sun is but one of millions--the fixed stars. Show the burning effect of a lens.

2. FUELS.--Wood, oil, coal, alcohol, gas, peat, straw: where obtained; special uses of each under varying conditions; need of economy. (This is closely related to geography.)

3. ELECTRICITY.--In urban schools use the electric light or some heating device for illustration. In rural schools a battery of two or three cells (see "Apparatus") will melt a fine strand drawn from a picture wire.

Applications: ironing, toasting, cooking; advantages or disadvantages compared with gas or wood.

4. FRICTION.--Pupils rub hands together; rub a button on a cloth; saw a string across the edge of a board or across the hand; bore a hole through a hardwood plank, then feel the auger-bit.

Applications: restoring circulation; "hot-boxes" in machinery; lubricants and their uses; lighting matches.

5. POUNDING.--Hammer a nail flat on an anvil or stone; feel it. Bullets fired against an iron or stone surface may be picked up very hot. Note sparks that can be struck from a stone; percussion caps, flint-lock muskets.

6. PRESSURE.--After using a bicycle pump for some time, feel the bottom, also the top. If possible, examine an air-compressor and find out the means used for cooling the air.

7. SOURCES OF LIGHT.--Sun, moon, oil, tallow, gas, electricity, wax, acetylene; advantages of each; relative cost.

PRIMITIVE METHODS OF OBTAINING FIRE: Most savages obtain fire by friction; rubbing two pieces of wood together till hot enough to set fire to some dry, light material. The natives of Australia placed a flat piece of wood on the ground and pressed against this the end of a round piece, which they twirled rapidly with their hands till fire was produced. The North American Indians did the twirling with their bow strings; the Eskimo's plan is somewhat similar. It is impossible to say when flint and steel were first used, but we know they continued to be the chief means of producing fire till about 1834, when matches were invented. Let pupils try to produce fire by these means.

The earliest lamps consisted of shells, skulls of animals, and cup-shaped stones filled with fat or fish oils which burned on a wick of cloth or the pith of rushes. The Tibetans burn butter, the Eskimos whale- or seal-oil, the Arabians palm- or olive-oil. For outdoor lighting, torches carried in the hand were used till gas came into general use about 1792.

CONDUCTION

Give to four boys strips of copper, aluminium, wood, and glass, respectively. They hold these by one end and heat the other end till one or more are forced to drop the piece on account of the heat. The boys with the metals will soon find them hot throughout, but the other two will be able to hold on indefinitely. The teacher gives the terms "good conductor" and "poor conductor".

PROBLEMS

1. Are metals generally good conductors? Try with strips of zinc, lead, iron, a silver spoon.

2. Are all good conductors equally good? Devise a means of ascertaining. See _Science of Common Life_, Chapter VI; also _The Ontario High School Physics_, page 274.

3. Is water a good conductor?

Lists of good and poor conductors may then be made, the teacher adding to the list. Good: metals; poor: wood, horn, bone, cloth, leather, air, water, hair, asbestos, ashes, rock, earth.

PROBLEMS

1. If the interior of the earth is very hot, why do we not feel it?

2. How can the cold snow keep the earth warm?

3. Why does your hand freeze to metals but not to wood?

4. Let the children try to find other instances: wools or furs for clothing, fur coats on northern animals, feathers on birds, down quilts, tea cosies, sawdust for packing ice, double windows, wooden handles for hot irons, asbestos coating for steam pipes.

THE MINERS' SAFETY-LAMP: This is a most important application of conduction. Get from the tinsmith a piece of brass gauze six inches square. Raise the wick of the spirit-lamp causing it to give a high flame and bring the gauze down upon the flame till it touches the wick. Note that the flame does not rise above the gauze. Hold a piece of paper above the gauze near the flame and note that it does not take fire. Note also that the gauze soon becomes hot. The brass wires conduct the heat of the flame rapidly away so that there is not heat enough above the gauze to cause combustion. Now roll the gauze into a hollow cylinder, pin the edges together, insert a cork at each end, and have a short candle fastened to the lower one. Try to light the candle with the lamp through the gauze. It is not easily done.

The miner carries a lamp made like this, so that if he should be in the presence of the explosive gas, "fire damp", it would not explode because of the wire gauze shield.

CONVECTION

Water is not a conductor, how then is it heated?

Drop a few pieces of solid colouring matter, (analine blue, blueing, or potassium permanganate) into a beaker of cold water. Place the beaker over a heater and observe the coloured portion rise.

Wet sawdust will make a good substitute for the colouring matter. A sealing jar or even a tin cup will do instead of the beaker. The stove or a dish of hot water will take the place of the lamp.

PROBLEMS

1. Using a thermometer, see whether the water at the bottom is warmer than that at the top while the beaker is being heated.

2. Heat some oil and pour it over the surface of some cold water. Lower a thermometer into this. Does the water at the bottom soon become warm?

3. If your kitchen is provided with a hot-water tank, find out what part of the tank first becomes warm after the fire is lighted.

4. In bathing, where do you find the coldest water of a pond or still river? See _Science of Common Life_, Chapter VI; also _The Ontario High School Physics_, page 280.

CONVECTION IN GASES

A good apparatus may be made by cutting two holes one inch in diameter in one side of a chalk box, replace the lid with a piece of glass, place a lamp chimney over each hole and a lighted candle under one of the chimneys. Hold a piece of smoking touch-paper at each chimney in turn and note direction of air current.

APPLICATIONS

1. Winds are caused by the rising of air over heated areas, allowing cooler currents to take its place. (Geography)

2. Rooms are ventilated by heating some of the air more than the rest, thus producing a current. (Hygiene) Winds are nature's means of ventilating the earth.

RADIATION OF HEAT

This should be taken up as an introduction to dew, frost, winds, climate, etc.

1. Make an iron ball hot (the end of a poker will answer). Hold the hand a few inches below the iron. Does the heat reach the hand by convection? By conduction? By means of suitable questions, lead the pupil to see that it is not by convection, for the hand is below the hot object while heated air rises; it is not by conduction, for air is one of the very poorest conductors; moreover, the heat is felt instantly from the poker, but it takes an appreciable time for it to come by conduction and convection. We say this heat is _radiated_ from the iron. The velocity of radiated heat is about 186,000 miles a second.

2. The above experiment may be varied by bringing the hot iron gradually toward the bulb of the air thermometer and noting the greatest distance at which it will affect the thermometer.

It is by radiation that the sun's heat and light reach us. We get much of the heat of stoves, fire-places, and radiators by the same means.

Why does the earth cool off at night? Why does dew form? Why can no dew form on a cloudy night? Why is a mountain top or a desert so cold, especially at night?

3. Take two tin cans (baking powder boxes will answer) and make holes in the lids large enough to admit a thermometer. Blacken one box in the flame of an oil lamp. Fill both with boiling water and put in a cool place. Test with a thermometer from time to time. Which cools most rapidly?

4. Fill the tin cans with cold water, find the temperature, and then place them near a hot stove. Which warms faster? Usually dark or rough surfaces radiate heat and absorb heat faster than bright or smooth ones. An excellent way of testing this is to lay a black cloth and a white one side by side on the snow where the sun is shining brightly. The snow will melt more rapidly under the black cloth. Painted shingles may be substituted for the cloths. Try different colours. The day chosen should not be extremely cold.

PROBLEMS

1. Why should we have the outside of a tea-kettle, teapot, or hot-air shaft of a bright colour? Why should we have stoves and stove-pipes dull black?

2. Why does a coat of snow keep the earth warm?

3. Which is the warmest colour to wear in winter? Does this account for the colour of Arctic animals?

4. Which is the coolest colour to wear in the hot sun?

5. Gardeners sometimes strew the ground with coal-dust to help ripen their melons. Show the value of this.

6. Suggest a method of protecting a wall from the heat of a stove.