ain points on the seashore in the summer time we may
notice that about 9 o'clock in the morning a breeze will spring up from
the ocean and blow toward the land; this will increase in intensity
until about 2 o'clock in the afternoon, when it has reached its maximum
velocity, and from this time it gradually diminishes, until in the
evening there will be a season of calm, the same as there was in the
early morning. The explanation of this peculiar action of the air is
found in the fact that during the day the land is heated much more
rapidly on its surface than the water is.

The radiant energy from the sun is suddenly arrested at the surface of
the earth, which is heated to only a very shallow depth, while in the
water it is different; being transparent it is penetrated by the radiant
energy to a much greater depth and does not suddenly arrest it, as is
the case on land. As the sun rises and the rays strike in a more and
more vertical direction the earth becomes rapidly and intensely heated
at its surface, and this in turn heats the stratum of air next above it,
which is pressing on it with a force of fifteen pounds to the square
inch at sea-level. When air is heated it expands, and as it expands it
grows lighter. The stratum lying upon the earth as soon as it becomes
heated moves upward and its place is occupied by the heavier, cooler air
that flows in from the sides. We can now see that if there is a strong
ascending current of air on the land near the ocean the cooler air from
the surface of the ocean will flow in to take the place of the warmer
and lighter air that is driven upward, really by the force of gravity
which causes the heavier fluid to keep the lowest level. As the earth
grows hotter this movement is more and more rapid, which causes the
flow of colder air to be quickened, and hence the increasing force of
the wind as the sun mounts higher in the heavens. But when it has passed
the point of maximum heating intensity and the earth begins to cool by
radiation, the movements of air currents begin to slow up, until along
in the evening a point is reached where the surface of the earth and
that of the ocean are of equal temperature, and there is no longer any
cause for change of position in the air.

The earth heats up quickly, and it also cools quickly, especially if
there is green grass and vegetation. While they are poor conductors of
heat, they are excellent radiators, so that when the sun's rays are no
lon