of Energy in the Atmosphere. 465 



and sea, together with the unequal moisture of the air pro- 

 duced by it, the orographic conditions of the earth's surface, 

 and the diverse qualities of the soil of extensive connected 

 tracts of the same, form a chain of further disturbances in the 

 equilibrium of the temperature, pressure, moisture, and local 

 disturbances of motion of strata of air accumulated upon or 

 beside each other as currents, which will no doubt always 

 render any reliable weather-prophecies impossible. 



If, moreover, the aqueous vapour contained in the ascend- 

 ing air exerts no important influence on the magnitude of the 

 kinetic energy of the air in motion into which the energy of the 

 solar radiations, for the most part, is converted, i'v at any rate 

 produces this effect, that the atmosphere ceases to be homo- 

 geneous, since alternate strata of warm moist air and of 

 colder drier air are formed. I must refrain from entering 

 upon the local influence of these varying conditions, since 

 they belong to the domain of observational meteorology. 

 The same holds good of the large subject of local cyclones, 

 produced, on the one hand, by local maxima and miDima on 

 the earth's surface ; on the other hand, directly by local dis- 

 turbances of the neutral equilibrium. I will make only a 

 few remarks on the dynamics of the latter class : ascending 

 cyclones with a vertical axis of rotation. 



I have already shown that the violent motions of the air 

 which occur in local cyclones cannot be well explained as the 

 result of simple acceleration of the ascending air by over- 

 heating of the lower strata and by the aqueous vapour they 

 contain. It appears altogether inadmissible to take account 

 of the rarefaction produced at the centre of a cyclor e by the 

 centrifugal force of the masses of air circulating round it as 

 an accelerating force acting upon it. 



The comparative vacuum formed can produce suction only in 

 the direction of the axis of the cyclone, thus either raising the 

 water upon the surface over which it rotates, or drawing down 

 air from the higher regions of the atmosphere. The existence of 

 such a descending current of air within a tornado is confirmed 

 by the clear sky and quiet air often observed at its centre. We 

 must assume that the vis viva of the air hastening with 

 enormous velocity into the cyclone, and ascending in it, is 

 accumulated in repeated accelerating impulses, and that it 

 results from the greater velocity of the air in the higher 

 strata. We must then imagine a local cyclone as produced 

 by an impulse of suparheated air, due to some local cause or 

 other, given at the boundaries of an upper and lower tract of 

 disturbance of the neutral equilibrium of an atmosphere at 

 rest, which reaches the boundary of the upper cooled strata 



