The winds that blow hither and thither, vainly striving to restore
equilibrium to the atmosphere, burden themselves with the moisture
they absorb from the seas; and this moisture absorbs their heat,
retards their motion, and slowly modifies the forces which impel them.
Now when the saturated air, extending far above the surface of the
earth, and carried in its movements still higher, is relieved of an
incumbent weight of air, it becomes rarefied, and its temperature
and capacity for moisture are simultaneously diminished; its moisture,
suddenly precipitated, appears as a cloud, the particles of which
collect into rain-drops and fall to the earth. Thus the air suddenly
loses much of its weight, and instead of restoring equilibrium to
the troubled atmosphere, it introduces a new source of disturbance.
Though the weight of the air is diminished by the fall of rain, yet
the bulk is increased by the expansive force of the latent heat
which the condensed vapors set free. Thus the rainy air expands
upwards and flows outwards, and no longer able to balance the
pressure of the surrounding air, it is carried still higher by
inblowing winds, which rise in turn and continue the process, often
extending the storm over vast areas. The force of these movements is
measured partly by the force of latent heat set free, and partly by
the mechanical power of the rain-fall, a very small fraction of
which constitutes the water-power of all our rivers. Such a fruitful
source of disturbance, generated by so slight an accident as the
upward movement of the saturated air, expanded by its own agency to
so great an extent, so sudden and discontinuous in its action, so
obscure in its origin, and so distinct in its effects,--such a
phenomenon defies the powers of mathematical prediction, and rouses
all the winds to sedition.