THE growth of aviation has resulted in an urgent and intensive demand for accurate weather forecasting not only at ground-level but also at all heights now utilized by aircraft. Methods previously employed for determining aerological data hi the atmosphere have utilized kites, sounding balloons or aeroplanes to carry special instruments recording the temperature, pressure and humidity at various altitudes. A mimeographed report entitled “The Radio-Telemeter and its Importance to Aviation”, by R. W. Knight, has recently been circulated by the U.S. Civil Aeronautics Authority. This report discusses the general problem of determining aerological data by radio-sounding balloons, to which are attached transmitters emitting corrynig? tVve meteorological instruments. A somewhat detailed description is then given of the apparatus developed for this purpose by the Blue Hill Observatory of Harvard University. Illustrations are given of the complete radio transmitter, with the associated instruments for determining temperature, pressure and humidity. At the ground station, the signals are received on a simple pen-writing recorder, from which the aerological information can be observed while the balloon flight is in progress. A specimen record indicates that heights up to 72,000 ft. (14 miles) can be obtained by this type of apparatus. The U.S. authorities maintain a network of teletypewriter communication facilities for disseminating the weather data to other meteorological stations, while radio broadcasting is used for the benefit of airmen. Plans are in hand for extending to other parts of the United States this application of radio methods to aerological observations.