Ever since Thomas Graham proposed the employment of a “liquid transpiration” tube (i. e., a capillary viscometer) as a “colloidoscope” (30b), internal friction or resistance to shear has been one of the most frequently used properties in the investigation of colloidal dispersions. Although it soon became evident that this property is in certain instances a very sensitive indicator of differences and changes in the inner structure of dispersions, the exact relationship between internal friction and structure has unfortunately remained obscure. In spite of this shortcoming, the “colloidoscope” or an equivalent instrument has proved its value as an empirical tool for both scientific investigations and industrial control. To serve these purposes, attention has been directed particularly to the refinement of experimental methods and to the empirical correlation of observable quantities.