Von Siemens' recent Theories. 45 



diftereuces exist between the continental and insular types, since 

 on islands the morning minimum is unusually large and the 

 afternoon minimum so small as to disappear, while in continental 

 types the reverse conditions olDtain. 



Werner Von Siemens, in answering 8prung's criticism on his 

 general air currents, after repelling certain statements of Sprung, 

 describes his own theories, which are worthy of restating : 



1. All winds are caused by the disturbances of indifferent 

 equilibrium, and the motion of the air is to restore equilibrium. 



2. These disturbances are caused through overheating of the 

 layers of air near the surface of the earth l)y insolation, through 

 unsymmetrical cooling of the higher layers by radiation, and 

 through the heaping up of air masses caused by obstructions. 



3. The disturbances are adjusted b}^ ascending currents, wherein 

 the particular species of acceleration occurs in which the increase 

 of velocity is jjroportioned to the diminution of pressure. 



4. The upward currents correspond to equally great descend- 

 ing currents in which there is a decrease of velocity correspond- 

 ing to the acceleration in the upward velocity. 



o. If the region of overheating of the air is limited locally, a 

 local upward current reaching to the highest layers of air arises, 

 and whirlwinds appear with interior spirally ascending currents 

 and outside similar ^spiral descending currents. The result of 

 this is dispersion of the superfluous heat of the loAver air by 

 which the adiabatic equilibrium is disturbed throughout the 

 whole column of air taking part in the whirling motion. 



6. In case the region of disturbance of the indifferent (or 

 adiabatic) equilibrium is very extensive, as, for example, the 

 wdiole of the tropical zone, the temperature adjustment can no 

 longer be accomplished by locally ascending whirls, and a whirl- 

 ing current must then arise involving the whole atmosphere. 

 The same conditions apply to these as to the local whirls of 

 accelerated upward motion and retarded descent in such a man- 

 ner that the velocity at different altitudes arising from heat con- 

 verted to work is approximately proportional to the prevailing- 

 pressure at the place. 



7. In consequence of the meridional motion produced and 

 maintained by conversion of heat into work, the whole atmos- 

 phere in every latitude must rotate with apiDroximately the same 

 absolute velocity. Thus the meridional currents produced by 

 overheating combine with the currents embracina; the whole 



