kind of lens will magnify.

INFERENCE EXERCISE

Explain the following:

221. The water that forms rain comes from the ocean, yet the
rain is not salty.

222. Iron glows when it is very hot.

223. You can start a fire with sunlight by holding a reading
glass at the right distance above the fuel.

224. Big telescopes make it possible for us to see in detail
the surface structure of the moon.

225. A room is lighter if it has white walls than if it has
dark walls.

226. Iron is heated by a blacksmith before he shapes it.

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 these droplets,
it is reflected at all angles according to the way it strikes, as
shown in Figure 89.

[Illustration: FIG. 88. The sunlight is scattered (diffused) by
the clouds. The photograph shows in the foreground the Parliam