  While the effect of rotation on spectral lines is complicated in
rapidly-rotating stars because of the appreciable gravity-darkening effect
differing from line to line, it is possible to make use of this line-dependent
complexity to separately determine the equatorial rotation velocity (ve) and
the inclination angle (i) of rotational axis. Although line-widths of spectral
lines were traditionally used for this aim, we tried in this study to apply the
Fourier method, which utilizes the unambiguously determinable first-zero
frequency (sigma1) in the Fourier transform of line profile. Equipped with this
technique, we analyzed the profiles of HeI 4471 and MgII 4481 lines of six
rapidly-rotating (vesini~150-300km/s) late B-type stars, while comparing them
with the theoretical profiles simulated on a grid of models computed for
various combination of (ve, i). According to our calculation, sigma1 tends to
be larger than the classical value for given vesini. This excess progressively
grows with an increase in ve, and is larger for the He line than the Mg line,
which leads to sigma1He > sigma1Mg. It was shown that ve and i are separately
determinable from the intersection of two loci (sets of solutions reproducing
the observed sigma1 for each line) on the ve vs. i plane. Yet, line profiles
alone are not sufficient for their unique discrimination, for which photometric
information (such as colors) needs to be simultaneously employed.
