68 



THE DYNAMICAL THKOKY OF OASES. 



Determination of the Inequality of Pressure in different directions due to (/,< 



Motion of the Medium. 



Let iis put />,,'-.?. + ? and P&=P* + <I> ...................... (120). 



Then by equation (52), 



( 2M > A > + S ^OM. - * 



"''-*^^-^-^) J 



the last terra depending on diffusion; and if we omit in equation (75) terms 

 of three dimensions in f, rj, , which relate to conduction of heat, and neglect 

 quantities of the form rjp and pi?p, when not multiplied by the large coeffi- 

 cients k, kt, and i,, we get 



du , dv , dw\ 

 + dy + Tz) 



If the motion is not subject to any very rapid changes, as in all cases 



except that of the propagation of sound, we may neglect ~ . In a single 



ot 



system of molecules 



,; .-. ... JjU 



2p (du . (du dv 

 whence ?= __^_ |__^_ + _ + _ .................. {124) . 



If we make ^ rj*- =/* 



fj. will be the coefficient of viscosity, and we shall have by equation (120), 



du (du dv 



m-*(&+3j 



dv . (du dv 

 Ty-*(d- X + d y 



dw . (du dv 



