This investigation has been concerned with heat transfer between a jet and the inside surface of a circular cylinder whose axis was normal to the jet axis. Such a jet system could be used to direct cold air on to the inside surface of a sheet metal nozzle guide vane in a gas turbine engine. As will be seen later high rates of heat transfer can be obtained in the vicinity of the point of impingement, so that this method of cooling could be particularly valuable for reducing the temperature of a “hot spot.”