Abstract
Some consequences of the report by Herr and Pimentel of a cloud layer of condensed CO2 at about 25 km in the atmosphere of Mars are examined. It is shown that this means the average lapse rate below the con- densation level is an appreciable fraction of the adiabatic value. It is shown also that condensation of CO2 implies almost inevitably that H2O condenses as well at a lower level.