( 489 } 



virinl o(|iiati()n iis my Inllicr Ims done (ni- llic cNlcriuil pfossiiro niid 

 ioi- llic [)r('ssiir(' of llic iii()l(>ciil;ii- ;illi-;(cti(Hi in ('Iiaplcr II of liis 

 '\)v ('onliniiilcil y:\\\ den (ias- en \ iocisloriocsl.-ind" and Inr \\\r 

 foi-ccs ('xcntiialinu' in (•ollisioiis of Iwo nioiccnics in dicsc l'rocccdinLis 

 \()l. Lp. l.'J.S. Oei. I.SlhS. 



h'irsl, li()\v('\('r. I \n il! point (hiI. dial die \ irial ('(piahon nciMJ nol 

 iKH'cssariiy hc applicil lor a dcliinic (pianlily of maller, w liicli is 

 conlaiiic»! in a dcliiuh' xolnnic and (Micloscd witliin a soli<l wall, as 

 is llic nsnal mcliiod of applying;- il. Wc may as wel! ap|il\ tlial 

 ('(pialion lol' a pari ol" a iKHnoucncons phase, scparatcMJ hy aii 

 iniau'inai'y scpai'alinü' sni-facr IVoin liic siirronndinü' siihsiancc which 

 is in ihc same phase. ^Ve shall nol ah\ays lind f/ic smin' molccnlcs 

 ^\■ilhiJl ;-nch a sniTacc, ImiI we may as>iime. Ihal al Iwo dillereiil 

 iiislaiils /", and /., wc shall lind lln' smm' iniinhcr or al least with 

 \-ei-y ureal approximation the same nnmher of molccnlcs within it, 



;ind that the expression S^in.r will also lia\(' the same \alnc al 



llic instants /^ ami /... We may thcrd'orc pnl: 



d il.i: 



2L>n,r = 



an<l also the corrcspoiidiiiLi- cfpialions lor the ƒ/- and lor the z- 

 coordinalc. 



Fr<mi this wo ma\' dcdnce: 



ilin.r iliiiil i/inz 



(•>) 



In the case that \\(' may nculecl the \()lnme of the molccnlcs 

 with i-cuaf'l lo the Nolnmc in which they are conlainc<|. and lhal 

 we may assnme thai the molccidai' forces act in sncli a way thai 

 Ilie\ \ ield on aN'crau'c /ero for the force exercised on a molccnlc 

 within a homou-encons phase, the ri^hthand meniher ol' this e(pialion 

 h;i> onl\ a \alne at the Worder (tf the volume nnder consideration: 

 it max Ihcrclore he reduced l(t a snrrace-intcural. 



The leflhaiid memher of lhi> e(|nalion is independent of the circnm- 

 slance whether the space under consideralion i^ enclosed wilhiji 

 an imaiiinary scparalin.i:- surface or within a s(»lid wall, and in the 

 latter ca>c il is also (pnle independent of the |»ropcrlic> of this wall. 

 So the riuhlhand nicmher cannot depend n|)on llicsc circumslajiccs 



cither. in the case of a >olid wall we max write: 



Jf 



'•el for llie riuiitliand mendter 



I'rocecilinus iluviil Actul. Auislcnliuii. Vol, V. 



0. So w 



:v^ 



