Summary: The forces on an aerofoil have been measured at various angles of incidence for 0.5 < R < 2,000.Below R = 2 the lift is found to be given approximately by :—L, = (3/2) µlV sin 2xand the drag at all angles of incidence tends to:D = µlV.An approximate theoretical estimate is also given of the effect of spacing, on the drag of a series of flat plates at R → o.