The paper describes a wireless direction-finder free from ambiguity which has been developed for use in ships as well as on shore. In most forms of direction-finder it is customary to use a figure-of-eight reception characteristic for taking the directipn, and afterwards, by a separate operation, to resolve the. ambiguity. This second operation increases the time required for taking a bearing, and the main advantage of the new system is that the direction and sense are determined by a single operation.The principle involved is a combination of a figure-of- eight reception characteristic with a cardioid under conditions which ensure:—(1) That the minimum of the cardioid is coincident in direction with one zero of the figure-of-eight.(2) That the cardioid e.m.f. is in quadrature with that of the figure-of-eight.These conditions can be fairly easily satisfied for an instrument set up on shore, but special precautions are necessary when it is installed in a metal ship, owing to the effect of various parts of the ship and its rigging on the wireless wave.An analysis is made of the magnetic forces in the wave in the vicinity of a ship and of the e.m.f. induced in the receiver of the instrument, and it is shown that in all cases where direction-finding with simple apparatus is possible in a ship it is also possible to obtain a satisfactory performance from the new instrument. The deviations that would be expected in a typical Service ship with the new instrument are calculated.By suitable arrangements of circuits the deviations that are experienced with the new instrument can be reduced to the same deviations as would be obtained with the equivalent simple direction-finder in the same position; for example, witfr a fixed spaced-aerial instrument all deviations could be removed as in the case of a Bellini—Tosi system. Methods for effecting these corrections in the new system are discussed.Finally, the setting-up of the new instrument in a cruiser is described and an account of trials carried out, the results obtained, and a comparison with expected results, are given.