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This paper describes a medium-wave Adcock direction-finder capable of working over the wavelength range 750 to 2000 metres (frequency 400 to 150 kc.) with a pick-up factor between 3 and 5 metres. Under favourable conditions a bearing can be taken on a field strength of 10 microvolts per metre with a swing of less than 1Â°. When the field strength is 1 microvolt per metre the corresponding swing is Â± 10Â°. The standard wave error is less than 1Â° as measured on a wavelength of 1 760 metres (frequency 170 kc), and this may most probably be taken to be representative of its value over the whole range. The instrumental error after balancing is less than 1Â°, but no information is at present available as to how long the balance remains constant. The instrument may therefore be said to constitute a practical development of the balanced-coupled Adcock system, retaining all the advantages of that type as regards polarization error but with a greatly enhanced pick-up factor compared with that of the early experimental model, which makes the apparatus capable of taking bearings with field strengths as low as 1 microvolt per metre, and with an instrumentalaccuracy as good as that of a loop-type BelliniÂ¿Tosi direction-finder.