158 LIGHT AND SOUND 



176. Diffused Light. When a reflecting surface is 

 rough, the light striking it is dispersed in all directions. 

 It is by diffused light that we see most objects. Daylight 

 is sunlight dispersed by reflection from the ground, trees, 

 houses, dust, clouds, etc. Moonlight is uniformly diffused 

 sunlight from the moon's surface. We see the " old moon 

 in the new moon's arms " by earthshine; 

 that is, by sunlight that has been re- 

 flected by the earth to the moon, and 

 has then come back to the earth. 



FIG. 150. 177 Refraction of Light. Let us 



If an object under water is 



suppose that in Fig. 150 we have a 

 ne s a rer u the?urface n> and vessel partly filled with water, and that 



we drop a stone (S) into it. To the 

 eye the stone does not appear to be S, but a little to one 

 side, and nearer the surface; that is, at S f . 



The explanation is that water is denser than air (cf. 

 33), and that the light which comes from the stone to the 

 eye is bent at B, where it passes from water into air. It 

 is bent away from the direction of the line SB. Since we 

 see an object in the direction which its light has as it 

 enters the eye, the stone appears to be at S'. 



Because light is refracted in passing from water into air, the water 

 of a pond or stream seems to be more shallow 

 than it really is, and a reed or an oar seems to be 

 bent where it enters the water. For a similar reason 

 a star near the horizon appears to be higher up 

 than it really is (Fig. 151). Its light is bent as 

 it enters the earth's atmosphere (cf. 38) from A star F ^ ar 15 t 1 he hori . 

 outside space. The amount of bending increases as zon appears to be 

 the star's light approaches the earth, because the reliiy r is. up 



