182 ON THE GENERAL CIRCULATION OF THE ATMOSPHERE. 
remain constant. But why this must remain constant and what force 
could effect the enormous increment of the vis viva stored up in the 
rotary air mass, remain equally incomprehensible.* 
I pass now to another assumption of Ferrel’s, with which I cannot 
bring myself to agree. Itis this, 7.¢., that on an inclined surface of equal 
air pressure there can be a descent of the overlying air layers. It 
is just as impossible that there should be an impulse to tangential 
displacement on sloping isobaric surfaces as in the case of level sur- 
faces. That sucha displacement could not possibly exist is evident at 
once from the consideration that a descending stream of air, in case it 
actually begins at any time, must immediately develop a change of 
pressure destroying the equilibrium, and must at once produce a return 
current. It results from this that a continuously progressive heating 
ot the atmosphere, such as in reality (aside from disturbances) takes 
place from the polar regions down to the equator, furnishes no posst- 
bility fora meridional circulation such as Dove also has assumed. It 
is possible, in such an unequally heated atmosphere, to draw at all 
heights isobaric surfaces extending from the equator to the poles, on 
which no voluntary air motion can originate. 
In spite of the great rarefaction by the heat of the torrid zone, the 
atmosphere would nevertheless remain at rest if no disturbance of the 
neutral equilibrium took place in any part of it. The neutral equilib- 
rium, with theadiabatic temperature gradient belonging to it, is the true 
condition of the equilibrium and of the relative rest of the atmosphere. 
This means that (apart from all friction) no expenditure of work is re- 
quired to bring a mass of air from -one height to another; that is to 
say, that the energy consumed in the expansion of the air under pres- 
sure finds its equivalent in the loss of heat by cooling, and vice versa, 
The general prevalence of neutral equilibrium in the atmosphere is 
therefore the cause of its state of relative rest, and every-disturbance 
of this equilibrium is of the nature of an accumulation of energy and 
has a tendency to cause currents in the air and thus to restore the 
condition of neutral equilibrium. The origin of these disturbances 
is to be sought exclusively in the unequal heating of the air strata 
*I must therefore decidedly object to the explanatory statement of Dr. Sprung, 
“that my assumption of the constant velocity of rotation of the air would be subject 
to the same error, or at least one very near to it, that vitiated the whole conception of 
Hadley and Dove as to the influence of the earth’s rotation upon the motion of the 
air.” Dr. Sprung quotes, quite improperly as a warrant for this opinion, the memoir 
by von Hemholtz ‘‘ Upon atmospheric motions.” Von Hemholtz in this mathemati- 
cal investigation has treated the hypothetical case, viz: ‘If we consider a rotating 
ring of air, whose axis coincides with the earth’s axis, and which is displaced either 
northward or southward by the pressure of similar neighboring rings, then, accord- 
ing to the wel)-known general mechanical principle, the moment of rotation must 
remain constant.” Thisisundoubtedly correct, since in thisassumed case the pressure 
of neighboring rings does the work of acceleration, but the present question is this: 
Whether forces are demonstrably present which produce this displacing pressure? 
