364. =Colors of the Clouds.=--There is no more gorgeous display of colors than we sometimes see in the clouds at morning or evening, especially the latter. These colors are occasioned simply by refractions and reflections in the minute vesicles (§ 288) of which the clouds are composed. How simple are the materials, light, water, and air, and yet how grand and diversified are the results! [Illustration: Fig. 253.] [Illustration: Fig. 254.] 365. =The Rainbow.=--In producing the colors of the rainbow the materials are less even than in producing those of the clouds. They are only light and water. The colors come from the reflection and refraction of light in the drops of the falling rain. I will illustrate the manner in which these reflections and refractions take place. Take a single drop, represented in Fig. 253. Let S be a beam from the sun. This entering the drop at A, is refracted, and passes to B, at the farther side of the drop. Here a portion of it is lost by its proceeding on in the line B C. The remainder is reflected to D, and passes to E, being refracted as it thus passes out into a rarer medium, the air. Here you have a single reflection and two refractions. But in the second bow, which is sometimes formed, there are two reflections as well as two refractions, as represented in Fig. 254. The beam of light, S, from the sun enters the drop at A, is refracted, and passes to B. Here a portion proceeds on in the direction B C. The other portion is reflected to D. Then this is lessened by a part of it proceeding on in the line D E. What remains is reflected to E. You see here the reason that the second bow is not so bright as the primary one. In the latter there is but one reflection in each drop, and therefore there is but one point where there is loss of light by its passing on out of the drop; while in the former there are two reflections, and therefore loss at two points. [Illustration: Fig. 255.]