256 



THE WORLD'S ADVANCE 



This movable exploring coil is attached 

 to a handle which carries a pointer mov- 

 ing over a graduated 36o-degree scale on 

 which the reading of direction is taken. 

 The exploring coil is connected to the 

 wireless receiver and the direction of the 

 arriving wave or signal is indicated by 

 turning the index handle until the posi- 

 tion of maximum strength of signals is 

 found. With the goniometer placed so 

 that the zero position of the scale coin- 

 cides with the bow and stern line of 

 the vessel, the position of the pointer 

 when the signals are strongest in the 

 head telephones of the operator shows the 

 direction of the signals in reference to 

 the bow and stern line. The geographical 

 direction is then secured by a glance at 

 the ship's compass. If for any reason 

 the signals have about equal strength 

 over a considerable portion of the scale, 

 note is made of the pointer's position 

 when the signals die out, and with the 

 angle divider furnished with the set a 

 mean of the two readings is taken. 



The action of the received energy on 

 the aerial is interesting and is really the 

 keynote of the operation of the appara- 

 tus. Each triangular loop is a directional 

 aerial in the wireless telegraph sense of 

 the term, receiving best when its plane is 

 in the direction of the sending station. 

 When either of the aerials is at right 

 angles to the direction of the incoming 

 signals nothing is heard; in intermediate 

 positions the induced current varies with 

 the angle and is set up in both aerials. 

 Carried to the goniometer, or direction 

 finding instrument, current of the same 

 relative strength passes through the cor- 

 responding crossed coils and forms in the 

 space enclosed by them two magnetic 

 fields at right angles to each other. These 

 two fields combine and form a field at 

 right angles to the direction from which 

 the signals are coming. The exploring 

 coil thus receives the signals strongest 

 when its plane is at right angles to this 

 field, or in the direction of the signals, 

 the pointer mounted on its spindle indi- 

 cating this position on the dial. 



An oscillatory circuit composed of a 

 condenser and a coil of wire is used for 

 testing, the instrument being adjusted to 

 the desired wave length by means of a 

 switch. The wires connecting with the 



aerial are taken past the coil at equal 

 distances, so that the two aerials are 

 equally excited. The buzzer is of the 

 type in which a non-inductive shunt is 

 connected across the magnet coils, spark- 

 ing at the contacts being thus reduced 

 and a sudden interruption obtained. 



When the direction of the wireless 

 station sending is indicated by the 

 pointer, only the line on which it lies is 

 given. That is, it may indicate a direc- 

 tion thirty degrees off the course of the 

 vessel, but it does not distinguish whether 

 this is off the port bow or its diametric 

 opposite, the starboard quarter. If the 

 test is being made with a land station 

 there is seldom any doubt of the direc- 

 tion, as it is generally known whether 

 the land lies to the port or starboard side 

 of the vessel. And whether the ship is 

 approaching or receding from the land 

 station is at once obvious; in most cases 

 there is only one possible interpretation 

 of the indication, for by the reverse in- 

 terpretation the ship would be some- 

 where inland and the land station out to 

 sea. Two successive readings while the 

 ship is on a fixed course place the mat- 

 ter beyond doubt and at the same time 

 give the distance to the station by the 

 usual nautical method. By taking simul- 

 taneous bearings of two fixed stations the 

 ship's position is easily reckoned. Or a 

 reading taken with a single fixed station 

 and a second observation made after the 

 ship has moved forward a definite dis- 

 tance in a straight course establishes the 

 position equally well. 



One of the things which the navigator 

 may learn through the wireless direction 

 finder is whether the ship is on a course 

 which will take him inside or outside a 

 lightship. The captains of many vessels 

 on the Atlantic lay their course for the 

 Nantucket lightship and after they have 

 made this isolated beacon trace their 

 course to another point. Often they run 

 inside the lightship and miss sighting the 

 vessel. A few signals from the wireless 

 equipment aboard her will secure the lo- 

 cation as certainly as if the light were 

 visible. 



When making a harbor a few signals 

 from the land wireless station show im- 

 mediately whether the ship has drifted to 

 one side of the entrance. 



