We observed the magnetic field of the CP star $\alpha^2$ CVn with the 6-m telescope and the echelle-spectrometer (spectral resolution $R=50000$, spectral range $\lambda\lambda 3400--4100$) using a CCD device and Zeeman analyzer. The longitudinal magnetic field $B_{\rm e}$ measured using lines with wavelengths shorter than the Balmer jump ($\lambda 3646$) are systematically 25% smaller at all rotational phases compared with measurements made in the region $\lambda > 3646$. Because in general lines with $\lambda > 3646$ form at deeper levels than lines with $\lambda < 3646$ we get additional evidence for the increase of $B_{\rm e}$ with depth in the atmosphere of $\alpha^2$ CVn.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html