52 Mr. T. Belt 07i the Origin of JF/iirlwinds. 



trade-winds are affected. Thus, suppose the cyclone A origi- 

 nates a few degrees south of the equator, and B and C are 

 currents of air moving towards it in opposite directions. The 

 course of the current B is from south to north ; but inasmuch 

 as the parallels of the earth's surface, over which it moves, in- 

 crease in velocity as it approaches the equator, and it does not 

 acquire this accelerated motion, it lags behind, and assumes a 

 direction west of the point towards which it is moving. 



The current C, on the contrary, is coming from regions 

 having a greater velocity than those at which it is constantly 

 arriving, so that it acquires an impetus towards the east ; and 

 this impulse is sufficient to determine the direction of the rota- 

 tion of the storm, which would otherwise be liable to take either 

 course indifferently. In the northern hemisphere it is evident 

 that the I'otation of the earth has an opposite effect upon the 

 meteor. 



As the cyclones progress towards the poles, they rapidly in- 

 crease in diameter and decrease in violence. Thus, when a 

 hurricane is met with within the tropics, its diameter will not 

 exceed 300 miles ; when it has reached the 50th parallel, it will 

 extend over 1500 miles. It is not only the ascending column 

 of air that acquires the rotatory motion, but the whole of the 

 air moving towards it must partake of it, and thus the dilatation 

 of the whirl increases as long as the cyclone lasts. It is pro- 

 bable that, compared with the extent of the whirlstorm, the 

 ascending column is of very small diameter. 



Concerning the recurving of the cyclones somewhere about 

 latitude 30^ in both hemispheres, I will only remark that I do 

 not consider it to be an inherent feature of a whirlstorm, but 

 rather to be impressed upon it by the line of laud forming the 

 boundary of the cyclone region. And this opinion is borne 

 out by the fact, that the cyclones on the eastern coast of Australia 

 recurve towards the west, following the line of coast. 



The electrical commotion and the heavy showers of rain and 

 hail accomjianying a cyclone may be bi'iefly glanced at. During 

 the heating of the lower strata of the atmosphere, and consequent 

 evaporation over the surface of the ocean, the vapour so gene- 

 rated will be partly diffused throughout the heated strata, and 

 will partly be formed into clouds on their higher limits. When 

 the cyclone bursts forth and the air rushes upwards, the vapour 

 at the outer edges of the vortex, where it comes into contact 

 with the colder atmosphere, will be precipitated in rain ; other 

 portions will be carried so high into the upper regions of the 

 atmosphere that they will not only be condensed, but congealed, 

 and fall in showers of hail. The vapour carried from the surface 

 of the ocean must be highly charged with electricity, which, as 



