  The Balmer lines of four A Ia - supergiants (spectral type A0 to A3) and
fourteen B Ia and Ib - supergiants (spectral type B0 to B3) in the solar
neighbourhood are analyzed by means of NLTE unified model atmospheres to
determine the properties of their stellar winds, in particular their wind
momenta. As in previous work for O-stars (Puls et al.) a tight relationship
between stellar wind momentum and luminosity (`WLR'') is found. However, the
WLR varies as function of spectral type. Wind momenta are strongest for
O-supergiants, then decrease from early B (B0 and B1) to mid B (B1.5 to B3)
spectral types and become stronger again for A-supergiants. The slope of the
WLR appears to be steeper for A- and mid B-supergiants than for O-supergiants.
The spectral type dependence is interpreted as an effect of ionization changing
the effective number and the line strength distribution function of spectral
lines absorbing photon momentum around the stellar flux maximum. This
interpretation needs to be confirmed by theoretical calculations for radiation
driven winds.
  A-supergiants in M31 observed with HIRES at the Keck telescope have wind
momenta compatible with their galactic counterparts.
  The potential of the WLR as a new, independent extragalactic distance
indicator is discussed. It is concluded that with ten to twenty objects,
photometry with HST and medium resolution spectroscopy with 8m-telescopes from
the ground distance moduli can be obtained with an accuracy of about 0.1m out
to the Virgo and Fornax clusters of galaxies.
