$P_{\mathrm{ram}}$. These are listed in Table \[table5\]. For the specific regions P08 and P09, the errors in the estimated shock velocities are great, as are the errors in $n_{\mathrm{0}}$. The region P20 is an incompletely radiative shock so therefore the measured \[\] electron density represents an under-estimate of the true density in the \[\] recombination zone.

In the final column of Table \[table5\] we give the time required for the post-shock plasma to cool to 1000K, $ t_{\mathrm{1000K}}$ measured in years. At this point, the optical forbidden lines are no longer emitted in the plasma, and hydrogen is less than 2% ionised, so the shock is essentially fully radiative. We may conclude that these cloud shocks are somewhat older than $ \left<t_{\mathrm{1000K}}\right> =410$yr (excluding P20).

[ The mean ram pressure for the clouds, $P_{\mathrm{ram}} = 3.1\times10^{-7}$dynes/cm$^2$ is much higher than the mean pressure in the X-ray plasma. This may be estimated using the proton densities and electron temperatures listed in @Williams06. This gives $7.6 \times 10^{-8}$ dynes cm$^{-2}$ in the NW region, and $5.3 \times 10^{-8}$ dynes cm$^{-2}$ in the S, for an average of $6.4 \times
10^{-8}$ dynes cm$^{-2}$. Thus the ram pressure in the cloud shocks is typically 