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. A storm not only disturbs the lower winds, but its influences reach even to the upper movements. The sudden expansion and rising of the rainy air delay these movements, which afterwards react as violent winds.