186 ON THE GENERAL CIRCULATION OF THE ATMOSPHERE. 
complete explanation. This change of condition of the lower strata 
by this mode of adjustment will continue just as long as the causes 
of disturbance in the upper strata continue. Till then, areas of low 
pressure with rising currents or areas of high pressure with a down- 
ward motion must prevail and set the atmosphere over an ex- 
tended region into cyclonic motion. Not till the air current in the 
higher strata of the atmosphere has again reached its normal relations, 
will a mean barometric pressure and relative rest again prevail at the 
earth’s surface. 
The theory of the general circulation of the atmosphere may now be 
summed up in the following principles: 
(1) All motions of the air originate in disturbances of the neutral 
equilibrium of the atmosphere and serve the purpose of restoring it. 
(2) These disturbances are brought about through overheating of the 
strata of air lying next to the earth’s surface by solar radiation, by 
unsymmetrical cooling of the higher strata by radiation, and by back- 
ing up of the moving masses of air in case of the occurrence of resist- 
ances to the current. 
(3) The disturbances are compensated by rising air currents having 
an acceleration of such magnitude that the increase of velocity is pro- 
portional to the decrease of air pressure. 
(4) Corresponding to the upward currents are equally great down- 
ward currents in which a diminution of velocity occurs comparable 
with the acceleration in the case of the rising current. 
(5) If the region of the overheating of the lower air is a restricted 
one, a local up-draft sets in which extends up to the highest part of the 
atmosphere, and presents the phenomena of whirl pillars, whose interior 
consists of spirally ascending currents and whose exterior is made up 
of similar spiral air currents directed downward. ‘The result of these 
vortex currents is to diffuse the surplus heat of the lower air by which 
the adiabatic equilibrium was destroyed throughout all the overlying 
air columns which take part in the vortex motion. F 
(6) In ease the region of disturbance of neutral (or adiabatic) equi- 
librium is very extended, so as for example to embrace the whole torrid 
zone, then the equalization of temperature no longer takes place by 
means of locally uprising vortex currents; now these currents must 
form and encompass the whole atmosphere. 
The conditions of accelerated uprise and of retarded down-flow laid 
down for the local whirl still hold good, so that the velocity of the 
air motion at different heights, developed by the energy of heat, is 
increased approximately in proportion to the air pressure there pre- 
vailing. 
(7) Since the whole atmosphere (in consequence of the continuous 
meridional circulation set up and maintained by the energy of heat) 
must rotate at all latitudes with approximately the same absolute 
velocity, the meridional currents produced by overheating unite with 
