ON THE GENERAL CIRCULATION OF THE ATMOSPHERE, 185 
and consequently in its compression under pressure, depends entirely 
on the degree of rarefaction produced, and upon the height of the 
ascent, then nearly the same diminution of temperature will take place 
in warm as in cold air. 
The excess of heat which the air possessed before the uprush must 
continue to pertain to the rarefied and cooled air, and hence, at all alti- 
tudes, temperature differences must exist of a magnitude similar to 
those at the surface of the earth. 
rom this basis, the condition of the atmosphere in general will not 
be that of unstable, but of stable equilibrium, since the higher air strata, 
on account of their equatorial tendency, will be on the average warmer 
and lighter than the adiabatic temperature gradient of the place over 
which they are found, requires. The higher the excess of tempera- 
ture of the air before its ascent and the more vapor it contains, the 
greater must be the velocity which it acquires in rising. In the higher 
strata of air of middle and high latitudes, relatively warm and. there- 
fore light currents of air of great velocity must alternate with the colder 
and slower flowing ones. 
Such a current of air, relatively light and warm, which takes entire 
or partial possession of the higher levels, destroys the neutral equilib- 
rium of the lower strata. At the surface of contact of the strata, the 
lower air which is relatively at rest must be under too great a pres- 
sure. It must therefore expand and be carried along by the lighter air 
which flows rapidly above it. 
As von Helmholtz has shown, this process must go on with great 
energy under a wave form, The result must be an expansion and 
up-fow of the lower air, which will continue until neutral equilibrium, 
disturbed by the diminished pressure of the upper strata, is again 
restored. 
The inverse case will occur where the air pressure of the upper strata 
is increased beyond the amount belonging to the elevation, by reason 
of cooling and of backing up, resulting from the narrowing of the 
current with increasing latitude. In this case there will be a settling 
down of the bounding strata. producing a condensation of the lower 
strata with a corresponding increase of pressure. Finally, in both 
vases, the disturbed neutral equilibrium must be restored through the 
action of upward or downward currents, by means of which the air 
strata lying beneath the sources of disturbance part with or take up 
air until neutral equilibrium is restored throughout the entire height 
of the atmosphere. 
In order to effect this, the air pressure of the lower strata must in- 
crease or diminish until it becomes adjusted to the pressure gradient 
of neutral equilibrium of the disturbing upper strata. That is to say, 
the pressure at the earth’s surface must change proportionately with the 
variation of pressure at the elevation itself, whereby the surprising 
magnitude of the changes of pressure at the earth’s surface find their 
