456 SHORT MEMOIRS ON METEOROLOGICAL SUBJECTS. 



has become uniformly distributed under a new horizontal surface lying 

 somewhat higher. If, on the contrary, a permanent stream flows into the 

 reservoir, the conditions are changed, since the surface of the water does 

 not come to a permanent stand until the influx and the efllux hold each 

 other in equilibrium; then, however, the surface of the water in the 

 reservoir, as well as every other level surface, has a descent toward the 

 efflux, which descent will then obtain over the upper surface of the 

 whole reservoir when the latter is full to the brim, and the point of 

 influx is, for instance, in the middle of the bottom of the reservoir. In 

 perfect accord with this also must be the condition in a permanently 

 rotating fluid, when a constant influx into it is taking place; for if a 

 permanent influx goes on from without at any point of a rotating mass 

 of water or other liquid, the pressure in the rotating mass will be 

 increased at all points, since the surface of the water, and, at the same 

 time, all the parallel level surfaces of constant pressures, must neces- 

 sarily take a higher stand, and an inclination to the original surfaces of 

 equilibrium corresponding to the influx from the point of influx outward 

 in all directions in which the fluid can flow away. 



If this is correct, however, and we further consider that a rotating 

 mass of air can resist the external atmospheric pressure only when the 

 velocity of rotation is of a determined magnitude, it will also be readily 

 seen, both that a great quantity of air must flow from without to the 

 rotating mass along the surface of the earth, and that this permanent 

 current of air must again flow away to the outside in the direction of 

 the level surfaces. When, furthermore, such a rotating mass of air 

 moves over the surface of the earth, it meets with manifold resistances, 

 which diminish its velocity of rotation, and give rise to those violent 

 gusts that are observed during the prevalence of hurricanes. The 

 diminution, thus occasioned, of the velocity of rotation at the surface of 

 the earth, then gives the superiority to the external pressure, and this pro- 

 duces both the aforementioned afflux of external air and the compression 

 of the air in the lower parts of the mass, whereby, on the other hand, the 

 air is again gradually driven away toward the exterior along the level 

 surfaces in proportion to its inflow below toward the center of the whirl. 



This explains the screw-shaped formation which is very often observed 

 during the prevalence of small whirlwinds, water-spouts, &c., since the 

 mass of air which rushes in from without along the surface of the earth 

 must, while so rushing in, be set into rotatory motion by the whirlwind. 

 It hereby also becomes evident that in a whirl the direction of the wind 

 along the surface of the earth cannot be perpendicular to the radius of 

 rotation, but on tbe contrary, and its inclination has been quite correctly 

 adduced by some meteorologists as a proof that an influx of air toward 

 the axis does occur in whirlwinds. It is manifest that the masses of 

 air which rush in along the surface of the earth must have, as is actually 

 observed in nature, a tendency to diminish the velocity of rotation and 

 to increase the diameter of the rotating mass. 



