above it, and rises just as a cork rises in water. You know that
hot air rises in the chimney; for if you put a piece of lighted
paper on the fire it is carried up by the draught of air, often
even before it can ignite. Now just as the hot air rises from
the fire, so it rises from the heated ground up into higher parts
of the atmosphere. and as it rises it leaves only thin air
behind it, and this cannot resist the strong cold air whose atoms
are struggling and trying to get free, and they rush in and fill
the space.

One of the simplest examples of wind is to be found at the
seaside. there in the daytime the land gets hot under the
sunshine, and heats the air, making it grow light and rise.
Meanwhile the sunshine on the water goes down deeper, and so does
not send back so many heat-waves into the air; consequently the
air on the top of the water is cooler and heavier, and it rushes
in from over the sea to fill up the space on the shore left by
the warm air as it rises. This is why the seaside is so pleasant
in hot weather. During the daytime a light sea-breeze nearly
always sets in from the sea to the land.

When night comes, however, then the land loses its heat very
quickly, because it has not stored it up and the land-air grows
cold; but the sea, which has been hoarding the sun-waves down in
its depths, now gives them up to the atmosphere above it, and the
sea-air becomes warm and rises. For this reason it is now the
turn of the cold air from the land to spread over the sea, and
you have a land-breeze blowing off the shore.

Again, the reason why there are such steady winds, called the