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? 230. What is said of steam? In what consists the power of the steam-engine? How is the expansive force of the steam in the boiler estimated? Describe the working of the engine by Fig. 210. 231. What is the difference between high and low pressure engines? What is said of the communication of heat? How many modes of communication are there, and what are they? What is the mode called convection? 232. Give examples of convection. What is the _conduction_ of heat? 233. State the experiment represented in Fig. 211. State the experiment represented in Fig. 212. What is said of non-conductors of heat? Give the examples cited. 234. Explain Davy's safety-lamp. 235. Give what is stated in the note about Stephenson and Davy. What is said of the influence of density on the conduction of heat? Give the illustration about melting snow. 236. State the experiments which show that liquids are poor conductors of heat. What is said of air as a non-conductor of heat? What is said of double windows? 237. What is said of arrangements of the walls of buildings? What of an arrangements for preventing the spreading of fires in blocks? 238. How are animals in very cold regions protected from the cold? What is it in their coverings that affords the protection? What is said of the coverings of quadrupeds that are natives of warm climates? What of the elephants whose remains are found in Siberia?