Interferometric observations of kinetic cooling

By using a three‐beam interferometer, the time constant associated with kinetic cooling has been measured as a function of water vapor concentration in atmospheres of N2 with fixed CO2 concentrations in the 400‐ to 800‐ppm range. Measurements have also been made in similar atmospheres with the addition of 10% O2. Least‐squares fits to the data are consistent with theoretical predictions when extrapolated to zero water vapor concentration. When water vapor is important, however, the experimentally observed relaxation times are considerably shorter than the predicted times.