Temperature distribution of neutral hydrogen at high galactic latitudes

Emission/absorption studies with the Arecibo 1420 MHz beam of neutral hydrogen at high galactic latitudes are reported. Ambiguities due to the finite beam-size are unimportant, and the range of spin temperatures is very broad. Either the interstellar medium contains some hydrogen at a few hundred degrees, or a physical correlation between hot and cold hydrogen exists. Absorption features of greater optical depth tend to have lower spin temperatures and lower velocities