THE KUTTA-JOUKOWSKY CONDITION IN THREE DIMENSIONAL FLOW IS DISCUSSED. THE CHARACTERISTICS OF THE SEPARATION LINE ALONG WHICH A VORTEX SHEET IS ATTACHED ON A WING ARE EXAMINED. FROM OBSERVATIONS OF THE FLOW OVER MARINE PROPELLERS AND DELTA WING MODELS, A DISCUSSION IS PRESENTED TO IMPROVE THE DESCRIPTION OF THE FLOW OVER ANY WING AND TO PROVIDE A BETTER BASIS FOR ACCURATE CALCULATIONS OF THE PERFECT FLUID FLOW USED AS A REFERENCE.