The statistical relation between wind and temperature in the lower stratosphere is not only of theoretical interest but is of practical concern for the operation of supersonic aircraft since for example the incidence of abnormally high temperature together with strong head-winds could substantially increase the time of flight and reduce the pay-load. Temperature and tail-wind component have been correlated on the great-circle route between London and New York at 50 mb. The route was divided into six legs of approximately 500 nautical miles; at the mid-point of each leg, temperature and tail-wind component for an eastbound flight were obtained from daily charts for the period of the International Geophysical Year and its extension, July 1957 to June 1959 (U.S. Weather Bureau, 1960–63). Seasonal correlation coefficients were evaluated for each leg and for the route as a whole. The seasons in the lower stratosphere in middle latitudes differ from the conventional seasons except in summer (June–August). Although autumn has been taken as September–November, it appears that the transition to the winter type of circulation is usually completed by late October so that November should strictly be included in winter. However, the period December to March has been taken for winter; conditions in March are very variable from one year to another but on balance this month is probably more appropriate to winter than to spring.