MECHANICAL EQUIVALENT OF PRESSURE MARGULES 519 



of the kinetic energy of the unit mass 



- (G 2 - G 2 ) = RT Po P 



_ Po-P 



1*0 



The following small table gives the velocity that a mass of air 

 acquires in passing horizontally and without friction through a 

 stationary field from rest and the pressure corresponding to 76o mm 

 mercury to a pressure that is less by i 3o mm . It is com- 

 puted 1 from this last equation, assumingi?r o = 287.273 w 2 sec -2 . 



Computed G, assuming no friction and small changes of pressure. 



p = 760 and G = 



From this table we may perceive to what linear distance a 

 horizontal current of air, in a steady field, can flow, frictionless, 

 against a given gradient. If its initial velocity is 20 meters per 

 second then this sinks to zero as soon as the pressure rises by 2/760 

 of the initial pressure. With an initial velocity three times as 

 great, or a living force nine times as great, it can overcome a dif- 

 ference of pressure of i8 mm mercury in the lower horizontal layer. 



(b.) Horizontal motion in a variable field of pressure 

 Equation III now becomes 



1 dG> 



2 dt 



1 dp 1 dp 

 - — — + — — 



pt dt pt dt 



1 Compare p. 416 of the recently published Lehrbuch by Hann, where these 

 same results are deduced in another way. — Abbe. 



