  We investigate the power spectrum of velocity fluctuations in the universe,
$V^2(k)$, starting from four different measures of velocity: (1) the power
spectrum of velocity fluctuations from peculiar velocities of galaxies; (2) the
rms peculiar velocity of galaxy clusters; (3) the power spectrum of velocity
fluctuations from the power spectrum of density fluctuations in the galaxy
distribution; (4) and the bulk velocity from peculiar velocities of galaxies.
We show that measures (1) and (2) are not consistent with each other and either
the power spectrum from peculiar velocities of galaxies is overestimated or the
rms cluster peculiar velocity is underestimated. The amplitude of velocity
fluctuations derived from the galaxy distribution (measure 3) depends on the
parameter $\beta$. We estimate the parameter $\beta$ on the basis of measures
(2) and (4). The power spectrum of velocity fluctuations from the galaxy
distribution in the Stromlo-APM redshift survey is consistent with the observed
rms cluster velocity and with the observed large-scale bulk flow when the
parameter $\beta$ is in the range 0.4-0.5. In this case the value of the
function $V(k)$ at wavelength $\lambda=120h^{-1}$Mpc is $\sim 350$ km s$^{-1}$
and the rms amplitude of the bulk flow at the radius $r=60h^{-1}$ Mpc is $\sim
340$ km s$^{-1}$. The velocity dispersion of galaxy systems originates mostly
from the large-scale velocity fluctuations with wavelengths $\lambda
>100h^{-1}$ Mpc.
