Notes of Lessons: Physical Geography, Class III

[We have thought that it might be of use to our readers (in their own families) to publish from month to month during the current year, Notes of Lessons prepared by students of the House of Education for the pupils of the Practising School. We should like to say, however, that such a Lesson is never given as a tour de force, but is always an illustration or an expansion of some part of the children’s regular studies (in the Parents’ Review School), some passage in one or other of their school books.—Ed.]

Subject: Physical Geography • Group: Science • Class III • Average age: 12 1/2 • Time: 30 minutes

By Hilda M. Fountain
The Parents’ Review, 1903, pp. 688-689

Sketch of a Lesson on Periodical Winds

Objects

I. To train the pupils’ powers of inductive reasoning.

II. To help them to gain a clear idea of the causes of wind in general, and periodical winds in particular.

III. To connect these winds with the geography of South America which they have been studying.

Lesson

Step I.—To draw from the children that difference in the temperature of air is one cause of wind. Introduce the subject by asking what happens when a handful of snips of paper are thrown into the fire. Do the experiment before them if possible, and get them to infer from their observation that the snips are carried upwards, that the heated air is lighter than the cooler air surrounding the grate. Hence hot air is lighter than cold air.

Step II.—To draw from the children that the difference in degree of moisture is a cause of wind. Ask them if they have noticed what happens when damp clothes are put to dry near a fire, and let them tell that steam rises from them. Get them to draw from this the conclusion that damp air is lighter than dry air.

Step III.—Sum up what we have learnt from these two experiments. A current of air tends to flow from a cold to a hot region, from a dry to a damp. Draw attention to the fact that air is a material substance and has weight.

Step IV.—Draw from the children that there is on the globe always a store of cold air at the Poles ready to rush in and take the place of the heated air near the Equator. Hence in the Atlantic Ocean, where there is no land to interrupt the course of the wind, we might expect the wind to blow due north, north of the Equator, and due south, south of the Equator. Tell them that such is not the case.

That sailing vessels find it most convenient to sail with the wind, and when going to the Cape they go first to South America, calling at the Brazilian ports. Draw from the children that the winds must, therefore, blow from the north-east.

Step V.—Hence there must be some other cause which has not been accounted for. Ask the children what are the motions of the earth, and tell them that it is the rotation of the earth that affects the direction of the wind. Help them by questioning to realize that the earth rotates more rapidly at the Equator than elsewhere, owing to the greater distance which it has to turn round in the twenty-four hours. Hence a current of air starting from the north with a slow velocity from west to east does not acquire the rapid velocity of the earth at the Equator by the time it reaches that part of the earth, and the result is that it seems to lag behind, and so, instead of blowing from the north, it seems to come from the north-east. Illustrate by diagram.

Step VI.—Get the children to find out how the wind blows south of the Equator, viz., from the south-east. Give the name of Trade Winds, and give some idea of their importance to navigation before steam power was employed. They blow all the year round in the Atlantic and Pacific Oceans.