The generally accepted theory as to cyclones attributes their initiatory formation to an unequal distribution of temperature with resulting mean diminution of pressure, and the movement of the air from places of high to places of low pressure, the lower air ascending with a gyratory motion, while air particles moving from opposite directions form couples which produce rotation. When energetic motions raise the ascending air to such a height that the temperature, cooled dynamically in ascending, goes below the dew-point, then the great store of latent heat thereby set free becomes, it is assumed, the main source of energy in maintaining the upward convectional movement. The subsidiary causes are attributed to the diminution of pressure on the collapse of the vapor, and also to the direct absorption of the sun's heat at the upper cloud surface.
In anticyclones a slow gyratory descending motion of the air is assumed. Ferrel considers the cyclone and anticyclone one system, and believes that air flowing into the cyclone from a "high" at the ground passes out into the higher atmospheric strata.
Dr. Hann has put forth the hypothesis that the genesis of cyclones and anticyclones may be sought in the general atmospheric circulation through a difference of temperature of the air from the equator to the poles. He speaks of a congestion in the upper or anti-trade winds, where the air heaps up to a great height, this being the cause of the anticyclones; and he maintains that the low temperature of the "high" is due to ground radiation, and that no part of the high pressure is the result of low temperature.
{ 43} To this hypothesis of Dr. Hann, ascribing the genesis of storms to the general circulation of the atmosphere, no application of the laws of dynamics has yet been made with a view of developing it into an acceptable "theory." If it should be established it does not follow that it will in any way affect the truth of the commonly accepted "convectional system," which, founded as it is on the well-known laws of thermo-dynamics, is not likely to be successfully assailed. There may be an improved nomenclature for the laws of statics and dynamics that will express to the mind more clearly the relation of cause and effect; but until the advance of scientific research modifies the present formulation of these laws the convectional theory will be generally accepted as giving the true interpretation of all the phenomena to which it could be applied.