FROM the earliest days of practical wireless com munication, it was realised that one of the most important services which this art would render to humanity was its contribution towards the safety of life at sea. The possibility of a ship being able to keep in communication with the remainder of the world during the longest voyages, and, in time of distress, to broadcast an appeal for assistance, has removed much of the terror of shipwreck and fire at sea. A later development, which bids fair to rank second in import ance to the above, is the direct application of wireless to aerial and marine navigation. There are, broadly, two methods by which a wireless signal may be used to determine the direction of any given fixed point. In the first, the direction of arrival of the signals from any transmitting station is determined by means of a direction-finder. The second method involves the transmission of a rotating beam of large or small angle and its reception on any suitable receiver.