  We present a method from an X-ray observation of a galaxy cluster to measure
the radial profile of the dark matter velocity dispersion, sigma_DM, and to
compare the dark matter ``temperature'' defined as mu m_p sigma_DM**2 / k_B
with the gas temperature. The method is applied to the XMM-Newton observation
of Abell 1795. The ratio between the specific energy of the dark matter and
that of the intracluster medium (ICM), which can be defined as beta_DM in
analogy with beta_spec, is found to be less than unity everywhere ranging
\~0.3-0.8. In other words, the ICM temperature is higher than the dark matter
``temperature'', even in the central region where the radiative cooling time is
short. A beta_DM value smaller than unity can most naturally be explained by
heating of the ICM. The excess energy of ICM is estimated to be ~1-3 keV per
particle.
