450 SHORT MEMOIRS OX METEOROLOGICAL SUBJECTS. 



u me toward the center, bat ceases just at the iuuer cylindrical surface 

 (since the velocity becomes imaginary) for all values of r < a, to which, 

 also, according to (3), correspond only imaginary level surfaces. By 

 I)assiug crosswise through such a rotating volume, one therefore meets, 

 as is easily seen, with conditions which harmonize with what is known 

 conceruing hurricanes iu the tropics, since the velocity of rotation in 

 the hurricane increases from the exterior inward toward the axis up to 

 a certain distance « from the same, where the hurricane reaches its 

 greatest violence, but beyond which even the most violent hurricane 

 is thereafter suddenly succeeded by an absolute calm, which continues 

 until one has passed to an equally great distance « beyond the axis. At 

 the instant when that distance is passed, the hurricane recommences 

 with the same violence as at the moment preceding its cessation, but 

 from the opposite quarter, and from this time forth the force of the 

 hurricane decreases in the same ratio as it had previously increased. 

 But in another respect also a remarkable agreement is found between 

 the rotating volumes of water under consideration and the rotating vol- 

 ume of air in a hurricane. It appears, namely, from formula (3) that 

 since the pressure upon a unit of surface of each level surface is equal 

 at all its points, and the pressure upon every point of the surface «] «i hi /9, 

 for which Sq = 0, is equal to tho pressure at «i &i in the ground lAane XY, 

 therefore the pressure must increase as we move over the ground plane 

 XY from the surface «i &i toward the exterior surface XY of the rotating 

 volume. If we are at the arbitrary distance C «?i = r from the axis CZ, 

 we have above us, beside the pressure at the point Oi, the pressure of a 

 column of water of the height w?i o = ^, and it is therefore evident that 

 the excess of pressure at the distance r = a-\- x from the axis above 

 the i)ressnre in the calm space iu the center of the rotating volume is 

 expressed by the weight of a column of water of the height s, as deter- 

 mined by formula (3). 



As now it is known, from the observations which have been made dur- 

 ing the prevalence of hurricanes, that conditions are met with iu these 

 rotating masses of air which correspond exactly to those which I have 

 pointed out in rotating masses of water, and as, moreover, I have shown 

 in a former jiaper, which will be found at page 1 of the Selskabets 

 Oversigter for Aaret 1865, that the laws of the movements of aeriform 

 bodies may be said, within the limit of accuracy with which the experi- 

 ments on the movements of fluids have hitherto been made, to be identi- 

 cal with the laws which govern the movements of liquids, if only the 

 diminution of pressure that occurs is represented by a column of the 

 fluid under consideration ; — I, therefore, believe that there is ground for 

 tho assumption that formula (1) will hold good not only for water, but 

 also for the movement of gases when the rotating mass is surrounded 

 by an exterior mass of air which resists its rotation. Experience must 

 decide whether I am right or not in basing my theory upon this hypothe- 

 sis. For the purpose of examining at once how far this theory of atmos- 



