  Measurements of the surface brightness distribution and of the velocity
dispersion profile have been so far used to infer the inner dynamics of
globular clusters. We show that those observations do not trace back the dark
matter potentially concealed in these systems in the form of low-mass compact
objects. We have built Michie models of globular clusters which contain both
massive and low-mass stars. An analytic expression for the stellar mass
densities has been explicitely derived in terms of the usual error function and
Dawson's integral. While the heavy population is kept fixed, the abundance of
the light species of our models is varied. When stellar velocities are
anisotropic, both the surface brightness and the velocity dispersion profiles
of the cluster become insensitive to the abundance of low-mass stars. This
suggests that the actual stellar mass function of many globular clusters is
still to be discovered.
