one day and night; so that as much as 22 feet, or a depth of
water about twice the height of an ordinary room, is silently and
invisibly lifted up from the whole surface of the ocean in one
year. It is true this is one of the hottest parts of the earth,
where the sun-waves are most active; but even in our
own country many feet of water are drawn up in the summer-time.

What, then, becomes of all this water? Let us follow it as it
struggles upwards to the sky. We see it in our imagination first
carrying layer after layer of air up with it from the sea till it
rises far above our heads and above the highest mountains. But
now, call to mind what happens to the air as it recedes from the
earth. Do you not remember that the air-atoms are always trying
to fly apart, and are only kept pressed together by the weight of
air above them? Well, so this water-laden air rises up, its
particles, no longer so much pressed together, begin to separate,
and as all work requires an expenditure of heat, the air becomes
colder, and then you know at once what must happen to the
invisible vapour, -- it will form into tiny water-drops, like the
steam from the kettle. And so, as the air rises and becomes
colder, the vapour gathers into the visible masses, and we can
see it hanging in the sky, and call it clouds. When these clouds
are highest they are about ten miles from the earth, but when
they are made of heavy drops and hang low down, they sometimes
come within a mile of the ground.

Look up at the clouds as you go home, and think that the water of
which they are made has all been drawn up invisibly through the
air. Not, however, necessarily here in London, for we have
already seen that air travels as wind all over the world, rushing