THEORY OF CYCLONES— VON BEZOLD 



361 



Hence in the cyclone, on account of the diminution of temperature 

 with altitude (even when the temperature at the'earth's surface does 

 not diminish with distance from this axis, as is the case in cyclones 

 with warm centers), the isobaric surfaces will gradually approach 

 each other wi*h increasing distance from the axis, but this approach 

 will always be relatively slight. 



It is entirely different with the critical surfaces; these rise very con- 

 siderably as one proceeds outward while the velocities increase with 

 the altitudes. 



Since in general the second term ofthe equation comes only slightly 

 into consideration, therefore the inclination of the isobaric surfaces 

 increases very nearly with the square of the wind velocity. 



If, therefore, in any cyclone the isobaric surfaces are such as is 

 shown by the full lines in fig. 55, and this frequently corre- 

 sponds to the actual conditions, and if this cyclone is centered for the 

 horizontal section A A , then it will not be so above or below this 

 section as the velocities increase with altitude. 



FIG. 55. ISOBARIC SURFACES AND CRITICAL SURFACES IN A CYCLONE 



Under this assumption the critical surfaces are arranged as is 

 suggested by the dotted lines in fig. 55, and therefore agree with the 

 isobaric surfaces only at the section A A, since there they have the 

 same common tangents. 



"Above this section the centrifugal forces are greater than the 

 gradient forces directed toward the axis and therefore movements 

 must occur opposed to the gradients." 



Hence the surfaces of this section A A, which is not necessarily 

 a plane but is here thought of as such for simplicity only, is the 

 boundary between a region of centripetal and centrifugal move- 

 ments. 



At the same time we easily see that such a reversal in the direction of 

 the movement must occur without change in the sign of thegradients 

 when the motion at the surface of the earth becomes approximately 

 circular. For since the velocities of the wind increase rapidly with 

 the altitude as shown by experience, while the inclination of the sur- 

 faces of pressure generally shows a diminution, therefore such a move- 



