Result. Water-vapour issues from the spout in an invisible form and becomes visible as a cloud some little distance above the level of the spout.
Deduction. That water-vapour is lighter than air.
Subject-matter of the earliest course in Physical Geography.
This course should include lessons on the following subjects:—
Subject-matter of early course in physical geography.1. Clouds: introducing the foregoing experiment to show why they occur high up in the atmosphere and how they are produced.
2. Rain, snow, hail, etc.: the different conditions under which clouds discharge their moisture.
3. Winds, with only such simple facts about their causes as can be shown by the movements of air or draughts in a room. If tissue paper be cut into fine strips, and held at different points in a room in which is a fire, the draught towards the fire may be simply demonstrated and also the draught up the chimney.
4. The sea: its saltness, the rising and the falling of the tide and the fact that high tide is later by nearly an hour every day, also that some tides rise higher and retire lower than others. (Causes of tides should not be touched upon till later.) Waves and their causes.
Definitions.As this course proceeds the children should be exercised in the making of good definitions. It is a mistake to think that definitions must be given by the teacher. It is well to ask one child what she means by the word to be defined. Write the definition on the board, and then, by means of a series of questions to the children, criticise all those points which are superfluous in the definition given. Having eliminated all these, let the teacher take the definition as it now stands, and by giving examples of all the facts which come under it, show that it is probably a great deal too wide, and draw from the children gradually all the necessary limitations.
A definition so obtained will be easily remembered, and, as the children get practice in framing them, they will appreciate the meaning and neatness of a clear definition.