278. By what simple experiment can you show the explanation of single vision to be correct? What is said of squinting? Explain the stereoscope.
279. What is said of distinct impressions on the retina? Explain the thaumatrope.
280. State in full what is said of the compound nature of light. Give the proportions of the colors in it. What is said about there being only three colors?
281. What is said of the recomposition of decomposed light? Give the illustration of the powder—the circular board—the top.
282. What is said of the colors of substances? What of the variations of these colors in different lights? What of variations with varying positions? What of the colors of clouds?
283. Explain the formation of the first rainbow by Fig. 253. Explain the formation of the second bow by Fig. 254.
284. What is said of the circumstances under which rainbows are seen?
285. Explain in full the formation of the two bows as illustrated by Fig. 255. What is said of the bow as seen by different persons, and at different moments by the same person? What of rainbow hues in dew-drops and ice-crystals?
286. Give the dissection of light as represented in Fig. 256. What is said of Daguerreotyping?