CHAPTER XII.

207. State the experiment of the three vessels, and the inference from it.

208. What other facts sustain this inference? How did Sir Humphrey Davy prove that there is heat in ice? What are the two theories of heat? What is the chief source of heat for the earth? What is said of the heat of the sun itself?

209. What is said of the universal influence of the heat of the sun in the earth? What of the heat supplied from within the earth itself? What of electricity as a source of heat?

210. What is said of chemical action as a source of heat? Give examples of the production of heat by mechanical action. What is said of the relations of heat and light?

211. Show the expansive influence of heat by describing the experiment represented in Fig. 192. Give familiar examples of this expansion.

212. How can you loosen a stopper stuck fast in a bottle? Give the anecdote about the _Persia_. Give the statement about the building in Paris.

213. What is said of the expansion of liquids by heat? How may the influence of this expansion upon specific gravity be shown?

214. What is said of thermometers? What of the invention of the thermometer?

215. State the plan of Fahrenheit's thermometer. Give the plans of other thermometers.

216. Why is Fahrenheit's thermometer, on the whole, the best? What is said of the expansion of gases by heat? State experiments in illustration.

217. What is said of balloons? What of the influence of heat on the atmosphere? Give examples of this influence.

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?

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?

239. What changes take place in the coverings of animals carried from a cold to a warm climate, and the reverse? Why has man no covering against the cold? Explain the object of clothing. What is said of articles of clothing? What of loose clothing? What of coatings of straw put on trees? What of bricks compared with stones?

240. What is said of cocoons? What of buds of plants in winter? What of snow as a protection of plants?

241. State the arrangement of snow observed in the arctic regions. State in full what is said of the influence of the conduction of heat upon sensation.

242. What is meant by the radiation of heat? Give examples of it. What is said of the connection of heat and light in the rays of the sun? What is said of heat from a common fire?

243. What is said of the relation between absorption and radiation? What of the reflection of heat? State the experiment with the mirrors and the thermometer and flask.

244. Explain the experiment with the ice. Give the experiment with phosphorus. Give the experiment represented in Fig. 218.

245. Explain the formation of dew. State the analogy of the tumbler. What is said of the circumstances that influence the deposition of dew and frost?

246. What is said of different substances in regard to the deposition of dew? What about Gideon's fleece? What is the dew-point? How can you ascertain in it?

247. What is said of the freezing of mercury? Explain the difference between sensible and latent heat. What is said of capacity for heat? State the experiment represented in Fig. 219.

248. What is the relation of heat to density? Give the illustrations.

249. What is the reason that the air is so cold on great heights? What is the relation of heat to the forms of substances? What is said of the melting of ice? What of the vaporization of water? State the general conclusion in regard to latent and sensible heat.

250. State in full what is said of latent heat in reference to clouds. Explain the operation of freezing mixtures.

251. State the examples of the production of cold by evaporation.

252. State and explain the experiment represented in Fig. 221.

253. Give the facts stated in regard to the degree of heat which man can endure. Give the reasons why the heat did not produce a greater effect in these cases.

254. What effect does heat produce upon the bulk of substances? What is said of water as an exception? Describe the process of freezing as illustrated by the diagram.

256. What would be the process if the exception did not exist? State what would be the results.

257. What would be the consequence if the freezing point were above 32°? What if it were below? What is said of the force of expansion in ice? What are some of the benefits which come from this expansion?