On Bekk's Smoothness of Paper

Measuring principle of Bekk's smoothness is analysed and it is clarified that there exists in measuring Bekk's smoothness excessive leakage of air which depends on permeability of paper and the roughness of paper of the opposite side of the tested surface. And so the excessive leakage is measured experimentally to be found out that it can not neglected for determining surface roughness of paper by Bekk's method.A direct reading instrument of smoothness of paper are designed applying a similar principle of air micrometer. Theoretical and experimental analyses show that a flow of air through spaces between a test surface and a flatly finished surface obeys Hagen-Poiseuille's law. From this respect the relation between a value of Bekk's smoothness and pressure drop of the new instrument can be given theoretically.Experimental researches show that the observations of smoothness of paper, which is obtained by the new instrument, coincide with those of Bekk's instrument when they are corrected by estimating the excessive leakage.