The Verdet constant of the Faraday rotation has been determined experimentally as a function of wavelength for optical glasses at 20 degree(s)C in the visible spectral range. Data have been analyzed for 40 different optical glasses. Very large values of the Verdet constant have been measured for the heavy flint glasses such as SF 59, SF 58, SF 57, and SF 6. On the other hand, very low values (within the experimental error close to zero) have been measured for SF L56 and SF L6. In order to fit the experimental data, a new dispersion formula has been derived on the basis of a simple oscillator model. It is shown that the experimental data of the Verdet constant as a function of wavelength can be fitted reasonably well by this new formula.