218. Why, in heating apartments, do we have the heat created or introduced at as low a place as possible? Explain the draught of a chimney. Why does a stove-pipe generally draw better than a chimney?
219. State the experiment with the candle and the door. What is the explanation of the occurrence of wind? Explain the land-breeze.
220. Explain the sea-breeze. How are winds affected by the rotation of the earth?
221. Show by Fig. 201 why the prevailing winds at the equator are northeast and southeast.
222. Mention the melting points of various substances. What is said about the natural state of water and other substances? What are the two modes of changing a liquid into vapor?
223. What is said of the rapidity of evaporation? What of the solution of water in air? What influence has heat upon the capability of air to dissolve water? What phenomena illustrate this? How is it supposed that water rises in air? What fact is in opposition to this supposition?
224. What becomes of the water that rises in the air? What is said of the formation of fog and of clouds? Mention the different shapes of clouds and their names.
226. What is said of the influences that give shape to clouds?
228. State how rain is produced, and explain Fig. 208. How are snow and hail formed? What is said of vaporization?
229. What influence has pressure upon the formation of vapor? Give the experiment with ether in illustration. Describe the experiment represented in Fig. 209. What is said of Papin's digester?