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 subst.i.tuted 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.
CHAPTER XI
FORM III
SPRING
WINDOW BOXES
Many garden plants should be started in a box of earth in a warm, sunny window. In some schools this can be done with a little care in heating on cold nights. Small boxes or grape baskets full of rich sandy loam with an inch of gravel in the bottom for drainage may be used. Sow the seeds in rows or broadcast. To prevent the soil from drying out too quickly, cover the box with a pane of gla.s.s. When the plants are up, give them plenty of light and not too much warmth. On very mild days set them in a warm, sheltered place out-of-doors and bring them in again early in the evening. This tends to make them hardy. When about three inches high, pick the young plants out and set them in other boxes a few inches apart. This moving causes the formation of numerous fibrous roots and makes stronger plants.
WINDOW GARDENS
Window boxes may be used for a whole season on the inside of the building in cold weather, and on the outside in warm weather. There is almost no limit to the kinds of plants that can be grown in them, but they are most suitable for flowers.
Good boxes may be made of dressed lumber so as to fit on the window-sill. They should be six inches deep, ten inches wide, and the required length. They should have a few small holes in the bottom to allow excess water to drain off and should be painted dark green or some quiet colour. There should be an inch of gravel in the bottom, some rotted sods covering this, and then the box filled with rich sandy loam.
SUITABLE PLANTS
Some flowers suitable for growing in window boxes outside in summer are those of drooping habit: lobelia, Kenilworth ivy, verbena, tropeolum, petunia, and sweet-alyssum toward the front, and behind, more erect plants, such as geranium, heliotrope, begonia, phlox, and nasturtium.
The box must not be too much crowded.
For inside and in shady situations the following are suitable: tradescantia, parlour ivy, moneywort, vinca smilax, climbing fern, asparagus fern, dracaena, coleus, centaurea, sword fern, and Boston fern.
For indoor boxes in winter, the following may be used: abutilon, calceolaria, cyclamen, violets, primroses, petunias, geraniums, freesia, and such foliage plants as dracaena, cannas, dusty miller, and coleus.
The following climbing plants may be trained up the window cases: asparagus plumosus fern, cobea scandens, smilax, maurandia, and English ivy. If drooping or trailing plants are desired, the following may be used: oxalis, sweet-alyssum, lobelia, ivy, geranium, Kenilworth ivy, and Wandering Jew.
FERTILIZER
As the amount of soil is limited and the number of plants that it has to support is great, the soil should be made quite rich and should be further fertilized from time to time with a little liquid manure. This can be best obtained by taking a strong barrel or large keg and filling it about half full of water. Then fill an ordinary coa.r.s.e potato sack with cow-stable manure and set the sack in the barrel for a few days. A tap in the bottom of the barrel is most convenient for drawing off the liquid manure. A little of this will also be found valuable for watering dahlias, roses, and other garden plants during the summer.
SOIL STUDIES
The cla.s.ses of soil should be reviewed. Pupils should gather examples from many places. The samples may be kept in bottles of uniform size and should include not only the four types but varieties of each, also various kinds of loam.
EXERCISES AND EXPERIMENTS
SOIL CONSt.i.tUENTS
1. With a sharp spade, cut a piece about twelve inches deep from (1) the forest floor, (2) an old pasture field. Note character and order of the layers of soil in (1) leaves, humus, loam, sand, or clay; in (2) gra.s.s, dead gra.s.s, humus, loam, sand, or clay. Observe soils shown in railway cuttings, freshly dug wells, post holes.
2. Note the effect produced on the soil of a field by (1) leaving it a few years in pasture, (2) ploughing in heavy crops, (3) applying barn-yard manure. In all these cases vegetable matter is mixed with the soil.
3. Dry some good leaf-mould. Throw a handful on the surface of some water. The mineral matter sinks, while the vegetable portion remains suspended for some time. Try this experiment with gravel, sand, and clay. Note that the gravel sinks rapidly, the sand less rapidly, and that the clay takes a long time to settle. If the water be kept in rapid motion, the finer soils will all remain suspended till motion becomes slower. Apply this in geography. The bed of a stream will consist of stones if it be swift, of sand if less swift, and of clay if very slow.
How are alluvial plains formed?
4. Place half an ounce of dry humus on an iron plate or fire-shovel and heat strongly in a stove. Note that it begins to smoke and a large part smoulders away to ashes; the mineral portion remains. Weigh the part left and find what fraction of the humus consisted of vegetable material.
Try to find the proportion of vegetable matter in each of the following: loams from various sources, sand, clay, gravel. The last three will show scarcely any change. This experiment will give rise to some good arithmetical problems in fractions.
WATER IN SOILS
5. Compare a handful of fresh garden soil with the same soil dried. Note the glistening of the fresh soil, also its weight and darker colour. The fresh soil admits of packing though no water can be squeezed from it. In its best condition, the water of the soil adheres as a film of moisture about every particle. Free water is to be avoided since it excludes the air from the soil.
6. Equal weights of soils of different kinds and degrees of fineness are placed in funnels or in inverted bottles with bottoms removed. Water is then slowly added to each until it begins to drop from the lower end.
From this is seen (1) the great value of humus as a water holder, (2) the advantage of fine soil over coa.r.s.e. For retention of water by absorption, consult _Nature Study and Life_, Hodge, page 382.
7. Take two wooden boxes (chalk boxes will do), fill one box with moist sand and the other with moist leaf-mould. Weigh the boxes separately and leave them for three or four days in a warm room. Weigh again and note decrease from evaporation. The sand dries out much faster than the humus. Test with clay, gravel, and loam, also with mixtures of these and leaf-mould.
8. Take three paint cans; punch holes in the bottoms. Fill each with good soil well shaken down. Stand the cans in water till the tops are moist, then place them in a warm, dry place. Loosen the soil on the top of No. 1 to a depth of one inch; on No. 2 to a depth of two inches; leave No. 3 untouched. Find out after a few days which is drying out fastest. How may soil be treated so as to lessen evaporation of water?
DRAINAGE
9. Gravel and sand allow water to run away rapidly, but where the soil is fine or closely packed as in clay soils, under-drains are necessary (1) to carry off the surplus water, (2) to allow air to enter the soil, (3) to warm the soil (wet soil is colder than dry).
Take two equal-sized tin cans, make several holes in the bottom of one, place therein a layer of broken pottery or stones, and fill with good soil. Fill the other with similar soil but make no holes for drainage.