THE AERIAL OCEAN IN WHICH WE LIVE. >j\ 
breezes which it makes for us in our country walks. 
Did you ever try to run races on a very windy day? 
Ah ! then you feel the air strongly enough ; how it 
beats against your face and chest, and blows down 
your throat so as to take your breath away ; and what 
hard work it is to struggle against it! Stop for a 
moment and rest, and ask yourself, what is the wind ? 
Why does it blow sometimes one way and sometimes 
another, and sometimes not at all? 
Wind is nothing more than air moving 'across the 
surface of the earth, which as it passes along bends 
the tops of the trees, beats against the houses, pushes 
the ships along by their sails, turns the windmill, car- 
ries off the smoke from cities, whistles through the 
keyhole, and moans as it rushes down the valley. 
What makes the air restless? why should it not lie 
still all round the earth ? 
It is restless because, as you will remember, its 
atoms are kept pressed together near the earth by the 
weight of the air above, and they take every oppor- 
tunity, when they can find more room, to spread out 
violently and rush into the vacant space, and this rush 
we call a wind. 
Imagine a great number of active schoolboys all 
crowded into a room till they can scarcely move their 
arms and legs for the crush, and then suppose all at 
once a large door is opened. Will they not all come 
tumbling out pell-mell, one over the other, into the hall 
beyond, so that if you stood in their way you would 
most likely be knocked down? Well, just this hap- 
pens to the air-atoms ; when they find a space before 
them into which they can rush, they come on belter- 
