548 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 5 1 



tive and negative portions), the loss of energy by friction and the 

 work of the pressural forces are equal to each other. 



(Q) = °- Atmospheric motions are primarily dependent on the 

 heat communicated from without. But it is possible that for cer- 

 tain general movements of the air, it is not the absorption of heat 

 during their occurrence that is the determining factor but the 

 temporary distribution of pressure, temperature and velocity 

 throughout the mass of air. In the following pages we will treat 

 these latter movements as though there were no addition of heat 

 but only an effort to attain equilibrium as the result of some given 

 initial condition. 



It is a characteristic of every motion performed without exchange 

 of heat that the work done by the pressural forces is determined by 

 the initial and final stages alone. It is well known that the quantity 

 A has the significance of a potential energy under certain conditions 

 such as, when the mass is kept at constant temperature, or when 

 every elementary particle of mass behaves adiabatically. This 

 last condition is a special case of (Q) = o. In this case an inter- 

 change of heat within the interior of the mass is allowable, or such 

 additions and subtractions of heat as balance each other, or sum 

 up zero, during the whole time / under consideration. If we confine 

 ourselves to the case that (Q) = o during every element of time 

 then the changes of A and I are continuously equal to each other. 

 In the case of motion without increase of heat, the quantity A 

 that I have in other places 8 called the potential energy of the dis- 

 tribution of pressure becomes identical with the internal energy 

 of the mass. 



If (Q) = o then 



OK + (R) = - 6 (P + I) (6**) 



In this case P -f I is to be considered as the total potential energy 

 of the system; in the case of gaseous motions in a closed system this 

 expression has the same meaning as P alone in the case of motions 

 of rigid bodies or incompressible fluids under the influence of gravity. 

 One easily recognizes the meaning of I in the expression for the 

 potential energy if one considers the case of masses of air pushed 

 horizontally (by compression or expansion) out of the condi- 



8 Max Margules : Ueber den Arbeitswert einer Luf tdruckvertheilung und 

 .ueber die Erhaltung' der Druckunterschiede. Jubilaum des KK Central 

 Anstalt, Vienna. 1901. See No. XXIII of this collection of translations 



