Homogeneous Nucleation Measurements of Water Vapor in Helium

A determination of the homogeneous nucleation rate of water vapor in helium is made. A procedure is established for determining an ``effective'' adiabatic index which may be used to find the final temperature obtained in an isentropic expansion of a real gas. A numerical integration technique is employed in analyzing experimental data. Results for supersaturations near 5 agree closely with the Becker and Doring theory.