The refractive index (n) and thermal coefficient of the refractive index (dn/dt) are measured at four wavelengths for the diethylamine and triethylamine. The measurements are carried out using the Bellingham + Stanley model 60/ED high-accuracy Abbe refractometer. The optical permittivity (epsilon) and its variation with temperature are calculated. Applying the Cauchy equation, the following refractive properties are obtained: the optical dispersion dn/d lambda, the dielectric dispersion d epsilon/d lambda, the variation of -dn/dT, d epsilon/dT, as a function of wavelength (lambda), and Cauchy's constants against temperature. Additionally, molar refractivity versus temperature and wavelength are determined. (c) 2005 Elsevier Ltd. All rights reserved.