Thinning of Saturated Superfluid 4He Films During Critical and Sub- critical 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 \u3c T \u3c 1.6 K. The results appear to rule out critical flow effects as an explanation of Keller\u27s results