158 Common Science 



227. A dentist's mirror is concave; he sees your teeth enlarged 



in it. 



228. Good penholders usually have cork or rubber tips. 



229. A man's suit becomes shiny when it gets old. 



230. When you look at a window from the sidewalk, you frequently 



see images of the houses across the street. 



SECTION 26. Scattering of light : Diffusion. 

 Why is it that on a dark day the sun cannot be seen through 

 light clouds? 



Why do not the stars come out in the daytime ? 



If you were on the moon, you could see the stars in 

 the daytime. The sun would be shining even more 

 brightly than it does here, but the sky around the sun 

 would be pitch black, except for the stars shining out 

 of its blackness. The reason is that there is no air 

 on the moon to scatter the light. 



Why we cannot see the stars in the daytime. Most 

 of the sun's light that comes to the earth reaches us rather 

 directly ; that is why we can see the image of the sun. 

 But part of the sunlight is scattered by particles of air, 

 and that is why the whole sky is bright in the daytime. 

 You know, of course, that the blue sky is only the air that 

 surrounds the earth. Enough of the light is scattered 

 around to make the sky as bright as the stars look 

 from here ; so we cannot see the stars through the sky 

 in the daytime. 



How a cloud can hide the sun without cutting off all its 

 light. When a cloud drifts between us and the sun, we 

 no longer see the sun; yet the earth does not become 

 dark. The sun's light is evidently still reaching us. 

 The cloud is made of millions of very tiny droplets of 

 water. When the sunlight strikes the curved sides of 



