Condensation phenomena at different temperatures

The results of the early experiments of C. T. R. Wilson on the condensation of water vapour have been of importance to both pure and applied physics. They led to the development by Wilson himself of the cloud method of investigating atomic phenomena, and, in the hands of H. L. Callendar and others, they were applied to the thermodynamic theory of the steam turbine, especially in connection with the discharge of steam by nozzles. Wilson’s results, together with those of the earlier investigations of Coulier, Aitken, etc., may be summarised as follows : Suppose we have a glass vessel, the volume of which can be altered at will, containing, initially, a volume of air taken from the atmosphere of a room and saturated with water vapour at room temperature. If the air is allowed to expand suddenly to a volumev 2 ,so that the ratio of the final volume to the initial volume,v 2 /v 1 is slightly greater than one, a dense cloud of drops is formed in the vessel. On restoring the gas to its original volume, a second expansion like the first results in the formation of a similar cloud, but if this process is repeated a stage is reached when the clouds become thinner, the drops being correspondingly larger, and soon the result of an expansion is not a dense cloud of small drops, but a rain of quickly falling large ones. Further small expansions now result in no condensation throughout the gas.