This note corrects an error in a paper by other authors in the Journal. The equation relating thickness of a film (d) and interference patterns of infrared radiation is given: d= m 2n(V₁-V₂) where m is the number of peak maxima between measured interference peaks; n is the refractive index of the polymer; and V is the wave-number. When using two adjacent peak maxima, m=1, and the equation becomes d= 1 2n(DELTA...) where d is in centimeters. -- AATA