. 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.
. 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 wireless or by land-hne. It may here be remarked inciden- tally that by such means the position of enemy sub- marines, ships, headquarters, etc., using wireless during the war were determined. With certain modifications and adjustments, the above principle has been successfully applied to air- craft, and at least two main methods are in use. In the first of these the aircraft carries the direction-finding wireless apparatus. To find his position at any time, the aircraft operator selects two land stations whose positions he knows accurately. \\'hen these stations transmit, he takes a bearing to each of them by means of his direction-finding apparatus. These two read- ings (which only take a matter of some seconds) are sufficient to enable him to plot his position accurately on the map. A check can be obtained by taking the bearing to a third station. This method is of great
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