The penetration of tin in a float glass results in chemical composition and structural variations in the direction perpendicular to the tin surface layers but does not vary in the direction parallel to the tin surface layers. This, therefore, leads to a difference between the dielectric behaviour in each direction. It is obvious that the difference should be due to the tin surface layers. Therefore, the dielectric behaviour can be used to obtain information about the tin surface layers. Experiment and calculation shows that the dielectric constant in float glass is different in both directions, as mentioned above, and information on the tin surface layers is incuded in the curve of the dielectric constant in the direction parallel to the tin surface layers as a function of the inverse of the electrode distance.