. Discovery. Science. DISCOVERY 309 task, and is, in most cases, practically impossible. It is found, however, that signals can be received on a closed loop of w ire, and that this can be used in certain cases instead of an ordinar}' type of aerial. The loop consists of several turns of wire wound usually around the periphery of a large rectangular wooden frame. This is mounted so that it can be rotated conveniently about a vertical axis of symmetry in the plane of the coil. Expressed mathematically, the energy absorbed by the coil PQ (Fig. 2) at receiving station R from the transmitting stati
. Discovery. Science. DISCOVERY 309 task, and is, in most cases, practically impossible. It is found, however, that signals can be received on a closed loop of w ire, and that this can be used in certain cases instead of an ordinar}' type of aerial. The loop consists of several turns of wire wound usually around the periphery of a large rectangular wooden frame. This is mounted so that it can be rotated conveniently about a vertical axis of symmetry in the plane of the coil. Expressed mathematically, the energy absorbed by the coil PQ (Fig. 2) at receiving station R from the transmitting station T is proportional to cos 6, where 6 is the angle which the coil makes with the straight hne joining the transmitting and receiving stations. This energy' will be a maximum when 61=0, when the plane of the coil lies in the straight line joining the stations. In other words, signals received at R on coil PQ from station T will be loudest when PQ coincides with RT. The application of this principle to direction-finding is easy to see, for suppose the position of T is unknown. An observer at R listening to signals from T rotates the coil PQ until he finds the position in which the signals are loudest. He then knows that the coil PQ points to the unknown station. This is not sufficient to determine the posi-. tion of T, but if similar observations are made at a second station not in the same straight line as TR, the data are then sufficient to determine the exact position of T. Thus the position of the unknown wireless station X (Fig. 3) can be determined from observations made at two fixed stations Y and Z (Fig. 3). Mhen X transmits, Y and Z, by means of their direction- finding apparatus, read off the magnetic bearing to the unknown station as determined by the position of the rotating coil when signals from X are loudest. The point of intersection of these two bearings gives the position of X. Stations Y and Z are, of course, in communication with each other, either by wi
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