Heat flows and temperature gradients were measured in a stable atmosphere heated by the water during a United States east coast to Bermuda aeroplane flight. The flux was computed from , where w' and T' are the vertical velocities and temperature deviations of the individual gusts. It is found that the heat flow is directed up the gradient as predicted by Priestley (1954). The expression for the maximum heat flow to be expected derived by Priestley in terms of the standard deviation of the temperature fluctuations and the temperature gradient gives the correct order of magnitude for the observed flow.