==>In this proposal, more time is requested for COM_GLO
Cometary globules are are the nicest examples illustrating the interaction of
the  UV  photons  from  hot  stars  with  dark  clouds.  They have bright rims
associated to the ionization front which is dominating the dynamical evolution
of  the  cloud  and its potential to form stars (see the review by Cernicharo,
1991).  Shock  waves associated with the ionization front are expected to heat
the  medium,  and  to  process the dust grains releasing complex molecules and
refractory  compounds  to  the  gas phase. However, in the densest part of the
globule  the  dust  remains  unchanged.  The  presence of dust in all possible
states  makes  cometary globules the best laboratories to study the properties
of  the  cosmic  dust in general. We propose here a complete study of the dust
properties  by  the means of IR observations of a carefully selected sample of
globules  of  different  types  inside the Trifid HII region, and in different
evolutionary  states.  Additional  measurements  will be made of some spectral
lines  (SWS01  and  LWS01)  which  are  expected to play a crucial role in the
thermal balance of the cloud.
The unprecedent informations provided by these proposed observations, together
with  our on-going studies of the molecular content, and our detailed chemical
and  hydrodynamical  modelling,  will  lead  to  a  complete  picture  of such
spectacular  clouds,  and  will  supply a full description of the physical and
chemical properties of interstellar dust.