May 19, 1921] 



NATURE 



l^Z 



Direction-finding Wireless and Marine Navigation. 

 By J. J. Bennett. 



' I ""HE use of wireless telegraphy for direction- 

 -*■ finding- purposes, which came into vogue 

 in the Navy during the war, seems likely to 

 remain as a permanent auxiliary to sea naviga- 

 tion. France, the United States, and Canada 

 have each adopted the system, and it is under- 

 stood that Germany is maintaining some of the 

 stations which she erected for war purposes, 

 although definite information on the subject is 

 lacking. So far as Great Britain is concerned, 

 the Admiralty has established direction-finding 

 wireless stations at the Lizard and at Carnsore 

 Point ; and it is also continuing for the present the 

 stations at Berwick and Flamborough. Although 

 a nominal fee of only five shillings is charged for 

 giving a vessel a bearing by wireless, our mer- 

 chant service does not appear so ready to take 

 advantage of this assistance as it was anticipated 

 it would be. This attitude of indifference is prob- 

 ably due to the value of the system not being 

 understood sufficiently. Nevertheless, direction- 

 finding wireless has proved of great help to the 

 seaman on many occasions, and, beyond all doubt, 

 will grow in favour as the mercantile marine be- 

 comes more familiar with its working. 



The principal use of the system is to enable 

 the bearing of a vessel in open waters, or when 

 approaching pilotage waters, to be determined 

 from one or more fixed points by intersection. 

 All bearings thus obtained are the Great Circle 

 bearings at the place of observation, which may 

 be on shore or aboard ship, according to the 

 method employed. If proper care be exercised, 

 the average of error will be very small — less than 

 one degree. Experience has shown that day read- 

 ings over water are always trustworthy, and. 

 unless high land is close to the vessel, day read- 

 ings over land are approximately accurate. Night 

 readings over water are .approximately correct at 

 short ranges of about one hundred miles ; but 

 night readings over land and over long distances 

 are liable to error. Sunrise and sunset times 

 should both be avoided, as bearings then obtained 

 by wireless cannot be relied upon for accuracy. 



There are at least three methods of using 

 directional wireless to give ships their bearings 

 and position. One requires no special apparatus 

 in the ship, the others do. In the case of the first- 

 mentioned, any vessel fitted with wireless tele- 

 graphy can call up a shore station and ask for 

 a bearing. The station signals back that it is 

 ready to give the bearing ; then the vessel makes 

 her call sign continuously for a short period, 

 during which time the shore station ascertains 

 the bearing by means of its direction-finder, or 

 radiogoniometer, and then transmits to the vessel 

 her true bearing with the time at which it was 

 observed. Responsibility for accuracy rests, in 

 this instance, upon the station. If the vessel 

 requires simultaneous bearings from two stations 

 in order to obtain her position, she calls up the 

 NO. 2690, VOL. 107] 



controlling station of the shore group and states 

 her need. Both stations then determine simul- 

 taneously by their direction-finders the respective 

 bearings of the vessel; the controlling station 

 collects both bearings, and either transmits them 

 to the vessel, with the time at which they were 

 determined, or, if equipped with the necessary 

 instruments for the purpose, the station fixes the 

 position of the vessel as obtained from the bear- 

 ings and sends the information to the vessel. 

 The main disadvantage of this method is that 

 only one ship at a time is able to call up a 

 station. If more than one tried to do so, "jam- 

 ming" might result. Further, the distance over 

 which bearings can be obtained is limited to one 

 well within the maximum range of the ship's 

 installation. If the bearing only is transmitted. 



Fig. I. — Field of magnetic lines offeree through a 

 loop aerial. This aerial may be regarded as 

 inductive to the field of magnetic force of the 

 advancing waves in certain positions, but as 

 non-inductive in certain other positions. In 

 the figure, for the sake of simplicity in drawing, 

 it is assumed that the loop is being move 1 

 round the transmitting station so that its plane 

 is pointing at the station at the right hand or 

 maximum current position, and is facing the 

 transmitter at the lower or zero current 

 position. 



the ship must be furnished with special charts 

 or special tables of correction, as the bearings 

 obtained are the Great Circle bearings at the 

 shore station. 



As to the station itself, it must have a direction- 

 finding plant, as well as an ordinary wireless 

 transmitting installation. The plant consists of 

 wireless direction-finder set, tuning apparatus, re- 

 ceiving and amplifying set with accumulator bat- 

 teries, dry batteries, etc., and a small power plant 

 for charging purposes. Where two or more 

 stations are grouped together for co-ordinate 

 direction-finding work, the controlling one may 

 be equipped with wireless transmitting apparatus, 

 the others with direction-finding apparatus only, 

 and be connected with the master station by 

 telegraph or land telephone. Any ordinary shore 

 transmitting station is suitable for undertaking 

 communication with ships requiring bearings, so 



