A series of overlapping photographs taken from a aircraft flying straight and level can be used to indicate the strength and direction of the wind, by noting the displacement on successive prints of the centre of the photograph, which is assumed to represent accurately the position of the aircraft at the time the photograph was taken. The method has the advantage that an almost continuous record of the wind can be obtained; it can be used over virtually any ground surface (though not over the sea) and the results of a long flight can be fairly easily and rapidly assessed. No detailed identification of the ground on a map need be made.