Abeles (in E. Wolf (Ed.). Progress in Optics, North-Holland, 1968, p. 251) has shown that the processes of determination of the refractive index and thickness of a transparent film may be completely separated. When under varying incidence angle the relative reflectances of p-polarized light at a film-covered and uncovered substrate's surfaces become equal, this means that the angle of incidence coincides with the Brewster angle, theta(B1), of the ambient-film interface. From a complementary point of view, for a film with non-uniform thickness it is an angle where the interference fringes of all the interference patterns, corresponding to the different film thicknesses, disappear. Moreover, there is yet one angle, theta(B2), where a sample's reflection also ceases to depend on the film's thickness and the interference fringes disappear: this is the Brewster angle of the film-substrate interface. Since the reflectances from a growing film or from different places of a tapered film have the same values at these angles theta(B1) and theta(B2) the interference patterns should intersect each other at these specific points. For a weak absorptive film the diminution, due to film's absorption, of the reflectance at the angle theta(B1) allows us to determine the extinction coefficient of the film.