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? CHAPTER XIV. 258. What is Newton's theory of light? What is the undulatory theory? State the analogies to sound and heat. When is a body luminous? What are the sources of light?