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.