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?
259. How may you see that light moves in straight lines? State various familiar recognitions of this fact. Illustrate the fact that the intensity of light is inversely as the square of the distance.
260. What is said of the velocity of light in regard to ordinary distances? How long is light coming from the sun to the earth? What is said of the light coming to us from certain stars?
261. Give the observation of Roemer represented in Fig. 226.
262. What is said of the reflection of light? What of its reflection in relation to seeing? What of the images formed in mirrors?
263. Show by Fig. 228 why the image in a mirror seems to be as the same distance behind it that the object is before it. Explain by Fig. 229 the operation of the kaleidoscope.
264. Explain the operation of a concave mirror by Fig. 230. Explain that of a convex mirror by Fig. 231.
265. What is meant by the refraction of light? Illustrate its reflection in passing from a denser into a rarer medium. Then from a rarer into a denser.
266. How is the refraction in regard to a perpendicular in the two cases? Explain dawn and twilight. Explain what is represented in Fig. 234.
267. What are mirages? Describe the mirage which occurred at Ramsgate. Describe that seen by Captain Scoresby. Relate the incident which occurred at New Haven.