The following paper describes a series of experiments carried out with a rotating-loop beacon transmitter installed for the purpose at Fort Monckton, near Gosport. After an initial calibration of the beacon, a series of tests was carried out in various cross-channel ships between England, France, and the Channel Islands. In these tests the accuracy of the wireless bearings obtained from the beacon was measured at various distances and the range of the beacon for reliable working was ascertained. The night errors, which were encountered at the longer distances, were studied in more detail at various fixed positions, chosen to show the effect of transmission over sea and land respectively. In the later part of the investigation a comparison was made both at sea and on land between the bearings observed on the rotating beacon and those obtainable with a direction-finder used in the ordinary manner. From the results obtained the relative merits of the two systems of ascertaining wireless bearings for marine navigation purposes are briefly discussed.