41)4 ) 



hikes place : so thai part (liiriiiii- wliicli the latl<'r lako place 



2nfl 'piip space under euii^ideraliitii may not coiilaiii the center of' 

 any nioleciile. 



A\'<> will call lliat pari of llie time r din-inu' w Incdi the lormer 



T 

 I J 



T. Dni'ini:' the lime ' t the -^urlace element do is (piile in 



the >ame circumstances as an elenienl ol' a plane wall. Therefore it 

 will experience on axeraLic a pres>nre /'. Tlii> pre^ure /■'i>a(|nan- 

 til\ which we may dei-i\(' iVom the, \irial «'(piation ; in order to deter- 

 mine it. it is therejore not i-e(pnre(l to decide whether the considerations 



in c(.iiise<pience of w liicli we liinl /' e(|iial lo 



/', are cori'cci or 



jiol. lint wlien the former case lakes place, so dnrini:- the lime 



\\v are ceiMainh jn>titie(l in as>nminLL' that i/n doe> not experienci' 



an\' pressure. I he average pre»nre on t/o i> therelori' /'. 



i" 

 ^\'e nia\' lind the \alne of ii in lir>t approximation l»y delernninim' 

 the \dlunie /■ of the hatched space, and Wy as>nniin.L:' that the chance 

 that a cei-tain dednile molecule will lie within thai \dlume is e(pial 



to ■-„. If // denotes the total Ulimher of molecules, lliell the chance 



r 



thai the space contains a molecule will \n- represented hy " ..■ ^ ^" 

 average the \alue t»f ' u \n ill lie (Mpi.il to this chance: therejore in 

 lii-st approximation \ ƒ' = " . 



1 

 We lind l»y a simple calculation for '■ the \alue , -'^ '■"» n\ li<'i"e 



r = 2 o =: the radin- of a distance --jiliere. Therefore : 



1 



-'T ' ■ 



4 :; A 



/(.l — n 



y 



.-i /, 



The inleriial vii-ial / will tliei-elore We :> /'^^ ( ' s r ' '^"" 

 eipialion (.1) assinnes the folhiwinu' shape: 



