The question of whether the dielectric constant egr; exists (is well defined) for a finite fluid system of rigid dipolar molecules is reconsidered and reformulated. It is found that this question can most simply be expressed in terms of the behavior of the positionhyphen; and orientationhyphen;dependentdirectcorrelation functionc(r1, ohgr;1; r2, ohgr;2). It is shown that egr; exists ifcsatisfies the following two conditions: (a)csim;minus;phgr;sol; kTforverbar;r1minus;r2verbar; sgr;, where phgr; is the dipolehyphen;dipole potential and sgr; is a length which is large microscopically but small macroscopically. (b)c(r1, ohgr;1; r2, ohgr;2) is of the formc8lpar;verbar;r1minus;r2verbar;rpar;plus;Flpar;r1minus;r2rpar;:elpar;ohgr;1rpar;elpar;ohgr;2rpar;forverbar;r1minus;r2verbar; sgr;, where e(ohgr;) is the unit vector with orientation ohgr;. An explicit (and new) expression for egr; in terms ofcis automatically obtained; its applicability is ensured if the above conditions are satisfied. These results lend new intuition and insight into the question of the existence of egr;, and suggest a promising approach for future investigations of this question.
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