CXXXVIII. The thickness of the saturated helium II film

The average thickness of the saturated He II film on an aluminium foil has been measured by a gravimetric method. For the film in contact with the bulk liquid, values between 120 and 180 atomic layers (4·8 × 10-6 cm and 7·2 × 10-6 cm) have been observed, depending on the height of the specimen above the bulk liquid level. The average thickness is independent of temperature except within 0·006 degrees of the lambda point. The values obtained suggest a film profile d=11·8 × 10-6/h 1/2, where d is the actual film thickness in cm at a height h above the liquid level. For the He II film not in direct contact with the liquid, a thickness of 55 atomic layers (2·2 × 10-6 cm) has been observed, independent of temperature and position of the bulk liquid level. This value is discussed in terms of a lack of temperature equilibrium. Observations of the evaporation of the film by radiation influx have been made. The possibility that the disparity between the results of various film determinations may be due to differing conditions of heat influx is considered in the discussion.