Page:The Atlantic Monthly Volume 1.djvu/286

278 there are doubtless many centres or maxima of rain, and whether the wind move around or toward these centres, it would inevitably get confused.

The opinion, that the winds move around the central point or line of the storm, was strenuously maintained by the late Mr. Redfield, whose activity in his favorite pursuit has connected his name inseparably with meteorology. Others have maintained the same opinion, and the rotatory motion of the tropical hurricanes is offered as a principal proof. It is obvious from the causes of motion already considered, that, if the air is carried far, by its tendency toward a rainy district, it will acquire a secondary relative motion from its change of latitude; and this, in our hemisphere, if the air move toward the south, will be westward,—if toward the north, eastward. Hence the motion of the air from both directions toward a stormy district is deflected to the right side of the storm; and this gives rise to that motion from right to left which is observed in the hurricanes of the northern hemisphere.

To suppose, as many do, that regular winds, arising from constant and extensive causes, can come into bodily conflict and preserve their identity and original impetus for days, without immediate and strongly impelling forces to sustain their motion, implies a profound ignorance of mechanical science, and is little better than those ancient superstitions which gave a personal identity to the winds. The momentum of ordinary winds is a feeble force in comparison with those forces of pressure and friction which continually modify it. Hence sudden changes in the direction and intensity of winds must primarily arise from similar changes in these forces. But there are no known forces which change so suddenly, except the pressure and latent heat of suspended vapor; and therefore the fall of rain is the only adequate known cause of those storm-winds which, interpolated among the gentler winds, keep the atmosphere in perpetual commotion.

Storms have, however, certain habits and peculiarities, more or less regular and distinct, which depend upon locality and season. And this is what ought to be expected; for, though the storms themselves are essentially anomalous, yet many of the causes which cooperate to induce them are constant or periodic, while others are subject to but slight perturbations. It is obvious that no more moisture can be precipitated than has been evaporated, and that the winds only gain suddenly by the fall of rain the forces which they have lost at their leisure in the absorption of moisture. Thus the rage of the storm is kept within bounds, and though the exact period at which the winds are set free cannot be determined, yet their force and frequency must be subject to certain limitations. The study of the habits and peculiarities of storms is of the greatest importance to navigation and agriculture, and these arts have already been benefited by the labors of the meteorologist.

The lawlessness of the weather, within certain limitations, though discouraging to the physical philosopher, has yet its bright side for the student of final causes. The uses of the weather and its adaptation to organic life are subjects of untiring interest. The progression of the seasons, varied by differences of latitude, is also diversified and adapted to a fuller development of organic variety by irregularities of climate.

The regular alternations of day and night, summer and winter, dry seasons and wet, are adapted to those alternations of organic functions which belong to the economy of life. The vital forces of plants and of the lower orders of animals have not that self-determining capacity of change which is necessary to the complete development of life; but they persist in their present mode of action, and, when they are not modified by outward changes, reduce life to its simplest phases. Changes of growth are effected by those apparent hardships to which life is subject; and progression in new directions is effected by