THE viscosity of liquids is a subject which, so far as I know, has hitherto been without any general theoretical basis. No physical mechanism, for example, has ever been brought forward to account even for so simple and general a fact as the decrease of liquid viscosity with temperature, in contrast to the familiar and well explained increase of gaseous viscosity with temperature. As a result, the study has hitherto consisted largely of a collection of more or less well established empirical relations, mostly of limited scope.