Soon the watchful chipmonk sang out, " The
grassy side of the sod is quite warm now, and the
water is not so cold as it was. The sand is hot,
and the rock is very warm."

"That will do for the sunlight," rippled the
little stream. " Now you may bring the stone,
sod, water and sand to my thick button-bush, and
place them in its cool shadow. We will learn
which will give off its heat soonest." ''

They had not waited long, when the same
merry chirping voice was heard, telling them that
the sand was cooling very fast, and the rock a
little more slowly. But it was quite a while
before Chip felt any change in the other two. At
length he found that the sod was a little cooler
than the water. Then the brooklet was ready to
tell them more about how the earth heats the
atmosphere.
"Nearly the whole surface of our vaUey is
covered with grass, sand, rocks, trees and water,
upon which the sun shines every pleasant day.
THB ATMOSPMESM IN MOTION. 69

You have just found that all parts of this surface
are not warmed equally fast. The sand and rocks
heat quickly, while the trees and grass-lands warm
slowly, and the water still more so.
" You know, also, that sand and rocks give off
their heat sooner than trees, grass or wMer.
That is why the air above our sandy field is
warmer than it is over the pond, when the sun is
shining.
" But cool air will flow under and float warm
air, and so we find a breeze often flowing from our
pond towards the sandy field in the daytime.
