It is not possible at this stage to do more than hint at the possible alterations in navigational procedures which the new knowledge contained in Mr. Durst's paper on the accuracy of dead reckoning in the air logically leads to. This is so for two reasons. First, existing navigational procedures differ so widely between civil and military users (and amongst civil users themselves) that detailed modifications to existing procedures require separate consideration in the light of the different current navigational drills at present used. Secondly, only two particular areas of the world, the North Atlantic and Central Africa, were considered in the paper, though these are fairly representative of extra tropical and tropical latitudes (there will, of course, be variations from place to place owing to the known variability of the general circulation of the atmosphere). Nevertheless, the data obtained by the meteorological statisticians is of such interest and importance that certain broad applications suggest themselves.