SCIENTIFIC_ABSTRACT We propose to measure the far infrared continuum and the fine structure lines of CII (158 micron) and OI (63 micron) along cuts in a few carefully selected translucent cirrus clouds at high galactic latitude. The selected clouds have been studied in detail by the applicants and collaborators, and stringent constraits on the physical parameters like density and kinetic temperature are already available. The goal of this study is a direct measure of the cooling rate. These measurements will also provide the physical conditions of the emitting gas and an important test for the various proposed heating mechanisms. The selected clouds lie in the range of Av where the transition CII -> C -> CO is taking place. With these observations we will estimate the amount of ionized carbon in the clouds and investigate the above mentioned transition region. OBSERVATION_SUMMARY The following observations for each object are proposed: 1) OI and CII spectra at the central position (peak of 60 micron emission), at a position at the edge and one position outside the cloud which serves as a reference measurement. The LWS medium resolution grating line AOT (LWS02) will be used with 5 points per line and an oversampling factor of 2. The line flux limit to be reached is 10^-20 W/cm^2 for which 2314 s integration time per position is needed. 2) PHT photometry (PHT22) will be performed in the 60, 100, 160 and 200 micron filters, with a spacecraft time of 481 s per position. These observations will complement the IRAS measurements, and be used to determine the global continuum emission. 3) CII spectra with LWS02, and the same setting as for the observations under point 1), will be taken at 5 to 9 positions along each of the objects. The aim here is to trace the line strength along the object and relate it to the CO emission. The flux limits to be reached is the same as under point 1), the integration time is 314 s per position.