We propose to observe the cooling lines CII and OI (63 microm)
 in 2 clouds which will be observed with PHOT already in
 selected positions during the ISOPHOT guaranteed time programme.
 Our aim is to compare the CII and OI line emission to the FIR dust
 continuum emission in order to determine the efficiency of the
 photoelectric heating mechanism by observing cuts through the cloud
 edges. Also the role of PAHs in the heating balance will be studied.