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.
Pages:
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68