The polarisation of tau 's produced in Z decay is measured using 160 pb(-1)
of data accumulated at LEP by the ALEPH detector between 1990 and 1995. Th
e variation of the polarisation with polar angle yields the two parameters
A(e) = 0.1504 +/- 0.0068 and A(tau) = 0.1451 +/- 0.0059 which are consisten
t with the hypothesis of e-tau universality. Assuming universality, the val
ue A(e-tau) = 0.1474 +/- 0.0045 is obtained from which the effective weak m
ixing angle sin(2) theta (eff)(W) = 0.23147 +/- 0.00057 is derived.