74 
THE FAIRY-LAND OF SCIENCE. 
atoms of carbon and making carbonic acid. Then we 
can turn to trees and plants, and see them tearing these 
two apart again, holding the carbon fast and sending 
the invisible atoms of oxygen bounding back again 
into the air, ready to recommence work. We can 
picture all these air-atoms, whether of oxygen or nitro- 
gen, packed close together on the surface of the earth, 
and lying gradually farther and farther apart, as they 
have less weight above them, till they become so scat- 
tered that we can only detect them as they rub against 
the flying meteors which flash into light. We can feel 
this great weight of air pressing the limpet on to the 
rock ; and we can see it pressing up the mercury in 
the barometer and so enabling us to measure its 
weight. Lastly, every breath of wind that blows past 
us tells us how this aerial ocean is always moving to 
and fro on the face of the earth; and if we think for a 
moment how much bad air and bad matter it must 
carry away, as it goes from the crowded cities to be 
purified in the country, we can see how, in even this 
one way alone, it is a great blessing to us. 
Yet even now we have not mentioned many of the 
beauties of our atmosphere. It is the tiny particles 
floating in the air which scatter the light of the sun 
so that it spreads over the whole country and into 
shady places. The sun's rays always travel straight 
forward; .and in the moon, where there is no atmos- 
phere, there is no light anywhere except just where 
the rays fall. But on our earth the sun-waves hit 
against the myriads of particles in the air and glide 
off them into the corners of the room or the recesses 
of a shady lane, and so we have light spread before 
