  It is shown that the renormalisation group flow in coupling constant space
can be interpreted in terms of a dynamical equation for the couplings analogous
to viscous fluid flow under the action of a potential. For free scalar field
theory the flow is geodesic in two dimensions, while for $D \neq 2$ it is only
geodesic in certain limits, e.g. for vanishing external source. For the 1-D
Ising model the renormalisation flow is geodesic when the external magnetic
field vanishes.
