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marks are blotted from view by mists 

 or fogs. The French government, as 

 well, has made it possible for ships, 

 fitted with the compass, to determine 

 their positions through wireless signals 

 from the stations along the coast. 



The United States Radio Service is 

 now experimenting with the Bellini- 

 Tosi type of radio compass at Cape Cod 

 and the Telefunken compass at Fire 

 Island. The purpose of each is to en- 

 able the navigating officer of a vessel to 

 take bearings of wireless telegraph sta- 

 tions, in order to find the position of his 

 ship or to avoid collision with other 

 craft. It is not asserted that the bear- 

 ings taken exceed, or even equal in ac- 

 curacy, those taken with an accurate op- 

 tical instrument under favorable condi- 

 tions, but reliable bearings may be 

 obtained by radio, when direct optical 

 bearings may not be taken because of 

 unsettled weather, etc., and in making 

 harbors, in keeping to difficult channels, 

 and in avoiding collisions with other 

 vessels, when fog obliterates surround- 

 ing objects from view. 



Transmitting Distributors of the Tele- 

 funken Compass 



Both compasses are modifications of 

 the same principle. The Bellini-Tosi 

 type provides that the moving station, 

 whose position requires determination, 

 shall send signals to a fixed station. The 

 direction of receipt is determined at the 

 fixed station, and then transmitted by 

 wireless to the moving station. In the 

 Telefunken system, the fixed station 

 sends out signals and the moving station 

 determines from what direction they 

 are coming. In both arrangements it is 

 necessary that one of the stations should 

 be directive. 



Directive sending is accomplished by 

 special antennas, which are considerably 

 more complicated than those of the ordi- 

 nary undirective type, require greater 

 space, and are difficult to install on 

 movable stations, such as ships or aero- 

 planes. The system in which fixed sta- 

 tions send out directive signals, therefore, 

 appeared most feasible to German in- 

 ventors. In this case the movable re- 

 ceiver need only be equipped with an 

 ordinary antenna. The Telefunken com- 



Popular Science Monthly 



pass is so worked out, then, that it may 

 be installed only on shore. Some thirty- 

 two transmitting antennas are disposed 

 at equal distances around a circumfer- 

 ence of a circle 200 meters in diameter. 

 Each pair is joined up successively with 

 the transmitting apparatus by a rotary 

 distributor, and at each position a signal 

 corresponding to a point of the com- 

 pass is sent out. An operator on board 

 ship thus hears a succession of signals, 

 increasing gradually in strength to a 

 maximum and then dying away. The 

 loudest signal occurs at the moment the 

 shore operator is sending on the anten- 

 nas pointed in the direction of the re- 

 ceiver. All that is necessary for the 

 ship operator to do, then, to obtain the 

 bearing of the land station, is to note 

 the signal that is strongest. 



On the other hand, the Bellini-Tosi 

 arrangement is contrived so that it may 

 be installed on shipboard. The ship 

 thus fitted is enabled to get its bearing 

 from any wireless station on the coast 

 or inland, if within range of the ship's 

 wireless. The salient features of the 

 Bellini-Tosi system are two aerial loops 

 of equal size, suspended in vertical 

 planes crossing each other at right angles, 

 and a "radiogometer" or special receiv- 

 ing transformer, having two primary 

 coils of equal size and crossing each 

 other at right angles in vertical planes. 

 When a signal is received, currents are 

 induced in both aerials, their relative 

 strength depending on the direction of 

 the sending station with reference to the 

 planes of the two aerial loops. The 

 signal is loudest when the plane of the 

 aerial loop is the same as that of the 

 sending station, weakest when the planes 

 are at right angles. The induced cur- 

 rents pass through the corresponding 

 crossed coils in the instrument and pro- 

 duce, in the space enclosed by them, two 

 magnetic fields at right angles to each 

 other. The two fields have relative 

 strengths depending on the relative 

 strengths, depending on the relative 

 aerials, and they combine to form a re- 

 sultant field at right angles to the di- 

 rection from which signals are coming. 

 The pivoted secondary coil will conse- 

 quently receive the strongest signals 

 when its plane is in the direction from 

 which signals are coming. A pointer at- 



