2(54 PROFESSOR TAIT ON THE 



[If a very small, thin, disc were placed in the gas, with its plane parallel 

 to yz, and the steady state not thereby altered, the difference of pressures on its 

 sides would be 



" p /" ; ( ! »-(l+7H 



J 



or 



For ordinary pressures, and a temperature gradient 10° C. per inch, this is of 

 the order 10" 7 atmosphere only.] 



41. For the energy which passes per second per unit of area across cc = 0, 

 we must introduce into the first integrand of § 39 the additional factor 



-^-(v 2 — 2vxcos0\ ; 



and the result of operations similar to those for the number of particles is 



*=-! 



-/•<(7 + v)/*W0 (3> 



This expresses the excess of the energy passing from the negative to the 

 positive side of cc = 0, over that passing from positive to negative ; and, by (d) 

 of § 38 must be constant. 



42. To put (1) and (3) in a more convenient and more easily intelligible 

 form, note that because 



we have 

 But, by (2), 



Thus, by (1), 



»/=4 Pt-^vHv 



v 3 h' 7/ „ 

 v A II 



ri_ ll_ 

 n h ' 



/5 C 1 -C 3 ) . . . (1'.) 



Similarly (3) becomes 



Jh b <6pirs \2 



E =jl-6^(¥ C '- OC = + C ' <« 



