180 ON THE GENERAL CIRCULATION OF THE ATMOSPHERE. 
general system of winds is based, depends, in plain terms, on the equi- 
librium between the acceleration of the air in the equatorial updraft 
(caused by the overheating of the lowest air layers of the torrid zone 
by solar radiation) and the loss of energy which the transported air ex- 
periences in its course. The mixture of the air masses, which, without 
a “fundamental circulation,” must rotate with the velocity of the earth’s 
surface upon which they rest, is accomplished by it in the course of a 
thousand years. I have used the mathematical idea of the sudden fric- 
tionless mingling of air layers at all latitudes only in order to determine 
in a simple way the condition of motion both with respect to direction 
and magnitude already prevailing since a primitive period. Ferrel does 
not proceed, as I do, from a fundamental circulation which inter-changes 
the air layers rotating with their respective latitude velocities while 
moving forward and thereby gradually mixes them, but allows this 
mingling to be effected in a meridional direction by a frictionless dis- 
placement of the rotating rings of air at different latitudes, the reasons 
for which are not specifically given. This conception of the mode of 
mixture furnishes essentially the same basis for computation as mine, 
and Ferrel reaches the same results of computation so far as the diree- 
tion of the wind currents is concerned, But, on the other hand, there 
exists an essential difference in our results for the relative meridional 
wind force at the latitude of 55°, 
The assumption of Dr. Sprung that neither of the two theories can 
be regarded as completely correct I wholly agree with. In fact I have 
never considered my theory in any other light than as a first approxi- 
mation to the truth. With this idea I have left out of consideration in 
my computation complicated influences, such as that of the decrease of 
temperature toward the poles and that of the non-coincidence of the 
direction of the centrifugal force with the force of gravity. The latter 
fact, whose action is also left out of consideration, that rotating air 
masses in higher latitudes must everywhere have the tendency to move 
forward in great circles, and thus tend to move toward the equator, 
would cause a decrease of air pressure aS we approach the poles, and 
would consequently essentially impair the result of my computation of 
the mixing, if this tendency were not compensated by other forces which 
have an opposite effect. Itis not these, however, but other assumptions 
of a fundamental character which mark a very essential difference be- 
tween the two conceptions and lead to results quite at variance with 
one another. In the first place, I refer to Ferrel’s assumption that the 
so-called principle of areas, in the form of the conservation of the moment 
of rotation, applies to the displacement northward or southward of the 
air rotating with the earth’s surface. I can not agree with this, and 
must enter my decided protest against the idea that the conservation 
of the moment of rotation is applicable to the movement of the air. 
The law of areas, borrowed from astronomy, means that a mass 
which moves freely around another describes equal areas in equal 
