Thinning of saturated superfluid 4He films during critical and subcritical flow

We report measurements of the thickness of a saturated superfluid ⁴He film under conditions of both critical and subcritical flow. Thinning consistent to within 20% with the predictions of Kontorovich as applied to our apparatus is observed over the temperature range 1.2 < T < 1.6 K. The results appear to rule out critical flow effects as an explanation of Keller's results.