DISCOVERY 



93 



the beginning. All the great developments had taken 

 place in naval, military, and air force stations, both 

 mobile and fixed, and little time was left for improving 

 the design of apparatus for the mercantile marine. 

 As soon as the war was over, however, the technical 

 lessons gained were quickly applied to the design of 

 ships' sets. Old sets have now been o%'erhauled, and 

 when new ones are installed, their all-round efficiency 

 is far in advance of the pre-war type. In many of 

 the larger passenger steamers a long-range set, using 

 either the Valve or the Arc System, is being fitted, in 

 addition to the Spark set, and altogether the technical 

 arrangements are rapidly being brought into line 

 with the improvements made in the naval ship sets 

 during the war. Many naval requirements are, of 

 course, not applicable to the mercantile marine ; in fact, 

 the technical lines of development in the two services 

 can never run on exactly parallel lines, as a warship is 

 normally required to fit in for communication purposes 

 with a fleet in close touch, several ships of which may 

 be signalling simultaneously on different wave-lengths ; 

 whereas a merchant ship is normally acting as a more 

 or less isolated unit, always ready to receive a distress 

 call on the 600 metres wave-length from any ship at 

 extreme range. This means that for a warship very 

 selective apparatus is an absolute essential, and it 

 can be readily arranged, as a navy is a small unit 

 where control is easy ; but in the merchant service 

 great selectivity may often be a distinct disadvantage, 

 as calls from ships not accurately adjusted to the 

 wave-length intended may be missed, and it is impos- 

 sible at present to ensure that the apparatus in all 

 ships of all nations shall be accurately adjusted. 

 Selectivity, like Free Trade, is excellent if everj^one 

 else adopts it. 



Besides long-distance continuous wave sets, with 

 the possibility of telephony in the background, the 

 important advent of directional apparatus must be 

 noted. The wireless " direction finder " is becoming 

 of recognised value in navigation when other means 

 fail, as in fog. The apparatus is fitted in the wireless 

 office and is worked by the wireless operator. With 

 this apparatus the operator can obtain the bearing of 

 a wireless station relative to the fore and aft line of the 

 ship, and the actual position of the ship can be obtained 

 by the intersection of bearings from two or more stations. 

 Up to about 100 miles the bearings as set off on the 

 Mercator's chart are accurate enough for all practical 

 purposes, but for greater distances conversion tables 

 or charts on the gnomonic projection must be used. 

 In these charts great circles appear as straight lines 

 instead of as curves, as in the case of Mercator's, and 

 the fact that such charts are required for long distances 

 will be evident when it is remembered that wireless 

 waves travel along great circles over the surface of 



the globe. Usually the bearings obtained are correct 

 within two degrees, and greater accuracy is not often 

 required ; but errors mostly due to the bending effects 

 experienced by wireless waves, especially at night, do 

 sometimes give trouble. A number of ships have 

 been fitted with this direction-finding apparatus, and 

 have often proved its utility as an aid to navigation 

 in thick weather. There are some Government stations 

 designed and used solely for the purpose of giving 

 bearings to ships. In these cases the station takes 

 a bearing by receiving signals transmitted from 

 the ship, and communicates them to the ship. The 



LANDS ENDlfW^ 



POLDHU 



results are as a rule more accurate than those obtained 

 by having the directional apparatus in the ship; but 

 the advantage of the ship itself being able to obtain 

 its bearing from any ordinary station within range is so 

 great that the present tendency seems to be to increase 

 the number of ships fitted rather than the number of 

 stations. Another advantage of having the apparatus 

 on board is that in foggy weather it may be used for 

 obtaining the direction of another ship fitted with 

 wireless. Advances are also being made with direc- 

 tional transmission — that is, the transmission of wireless 

 waves in one direction only, instead of the usual all- 

 round radiation — an arrangement obviously of great 

 value for navigational purposes. 



