Transient natural convection response for external flow is determined experimentally and compared with the double integral theory predictions for processes wherein all transient effects are important. The theory is shown to give very accurate predictions of response for such processes. Similar agreement for the quasi-static and conduction dominated processes is discussed. The forms of the generalized thermal capacity and time variables arising in the theory are substantiated by the absence of a residual Prandtl number or Grashof number effect in comparing experimental response with predicted response. All measured responses are in agreement with the theory prediction that temperature overshoot does not occur for a vertical surface.