The radiation distribution of an antenna in a vertical plane was obtained by measuring in an aeroplane the strength of a received signal from an excited antenna on the ground. The position of the aeroplane relative to the antenna was obtained by means of a theodolite on the ground, the signal strength being recorded on a cinematograph film.Although the ground site appeared very good, it was found that spurious radiations were obtained and these were probably the cause of the discrepancies found between the theoretical and the experimental results. The measurements were made on a horizontal antenna at several frequencies. The reason for this particular arrangement is that it should be possible to separate the effect of the reflection of the antenna in the earth from that of the antenna itself, and thereby obtain a double result from a single measurement.The results showed very definite maxima and minima and the position of these could be ascertained accurately within a few degrees, but the difficulties of the experiment prevented an accurate value of the field strength being obtained. Substantial agreement was obtained between theory and experiment, the discrepancies increasing with the frequency.The radiation distribution was also obtained for one of the beam stations erected by the Marconi Co. Owing to the sharpness of the beam, considerable experimental error was liable to occur. Nevertheless, substantial agreement between theory and experiment was also obtained in this case.