Values of diffusion coefficients determined from the observed closing times of nine conical-shaped clearings in fog produced by hovering helicopters at Lewisburg, West Virginia, in September 1969 are presented. The values were established following the method of Elliott, assuming that the geometric and diffusive properties of the clearings and surroundings could be approximated by theoretical equations of the type governing the diffusion of heat and water substance in a bounded, circular cylinder of infinite length, with appropriate specification of the condensation conditions. The diffusion coefficients for the experiments ranged in value from 0.7 to 1.9 x 10 to the 5th power sqcm/sec. Summary diagrams are presented to illustrate how a cylindrical or slot-shaped clearing will close-in with time, dependent on the values of the diffusion coefficient and on the initial temperature and humidity differences between clearing and surrounding.

A selection of annotated references to unclassified reports and journal articles that were introduced into the NASA scientific and technical information system and announced in Scientific and technical aerospace reports (STAR) and International aerospace abstracts (IAA).