Part(1) describes a four-aerial direction-finding system erected at a site near the Radio Research Station, Slough, and gives details of the tests carried out on this apparatus at wavelengths of 300 to 600 m. The system is based on the Adcock principle, but a modification has been introduced to correct for the asymmetry of the aerial system with respect to its upper and lower portions which is unavoidable if the operating hut is at ground-level.In the first test the performance of the new direction-finding system was compared with that of a rotating-loop direction-finder over a prolonged period which included conditions of most severe “night effect.” In the second test a calibration of the system was made by means of a transmitter attached to a kite which provided a source of downcoming waves of known angle of incidence and polarization.The results of the tests show the new system to be considerably superior to the closed-loop system for conditions of “night effect.” They indicate, however, a residual instrumental error of the system in the presence of down-coming waves. Finally, a further modification of the system by which it is hoped this will be eliminated is described.Part(2) describes two distinct types of portable short-wave direction-finding apparatus and gives details of the methods by which they were tested and compared under working conditions at wavelengths of 12 to 60 m.The first instrument is of the totally-screened closed-loop type.The second instrument is of the rotating Adcock type consisting of a single pair of spaced vertical aerials pivoted about a vertical axis.The tests described are divided into four sections:—(a) Testa for instrumental error with a local transmitter situated first on the ground and then elevated 40 ft. above the ground with its aerial at various angles to the vertical to give waves of varying polarization.(b) Tests on the effects of the immediate surroundings of the receiver.(c) Direction-finding observations on the “ground ray” of a transmitter up to the maximum distance at which the ray is detectable.(d) Long-range tests at which only downcoming waves were being received.Test (a) showed the Adcock to be much superior to the loop in the presence of downcoming horizontally polarized waves, while, (b), (c) and (d) show that for observations on the ground ray both instruments are equally satisfactory and that with due precaution in the choice of a site their performance is much the same as that the of longer-wave apparatus. For observations just outside the range of the ground ray both systems are equally useless, while at greater ranges (beyond the “skip distance”) the results again demonstrate the superiority of the Adcock to the loop.It is shown that the results generally confirm the conclusions with respect to the nature of the propagation of the waves arrived at by Eckersley from somewhat similar experiments.