DISCOVERY 



307 



in naval and military operations and in commerce 

 was fully recognised, and suitable types of apparatus 

 were available for such purposes. With aircraft, 

 however, this was not the case. At the outbreak of 

 war the use of wireless in connection with aircraft had 

 not got beyond the initial experimental stage, and 

 no standard types of apparatus had been adopted. 

 The need for rapid and efficient communication between 

 jurcraft and the ground was urgent, and under the 

 stress of war conditions suitable types of apparatus 

 were devised and manufactured. During the years 

 of w-ar these changed very considerably as one im- 

 provement followed another, new developments took 

 place, and new conditions and increased functions 

 demanded new types. The development has been one 

 of triumphal progress ; enormous difficulties have been 

 overcome, with the result that to-day there is little 

 or nothing in connection with wireless on land or sea 

 which cannot also be done in the air. 



A wireless station, whether on land, on sea, or in 

 the air, requires {a) electrical power, (b) transmitting 

 and receiving apparatus, (c) an aerial, and {d) an 

 " earth." It is easy to make provision for all of these 

 on land or on ship, where sources of electrical power 

 are available, where an aerial can be erected on masts, 

 where an " earth " is obtained by contact with the 

 ground or with the sea, and where there is practically 

 no limit to the weight or bulk of the necessary appara- 

 tus. In the air, however, conditions are different ; as 

 the space available in aircraft is very limited, and 

 weights have to be reduced to a minimum, no large 

 or heavy power plant or apparatus can be carried. 

 The workmanship achieved in this direction during the 

 war was very fine ; transmitters of considerable range 

 for use chiefly in aeroplanes w-eighed only from 5 to 

 10 lb., while electric generators capable of producing 

 600 volts weighed about 18 lb. The source of power 

 for transmitters varied with the type : in earlier and 

 low-power sets accumulators were used, while later 

 sets usually obtained their pow-er from small wind- 

 driven generators. These were fitted to the aircraft in 

 a position in which they would experience the full 

 rush of air while flying ; this turned the windmill 

 propellor attached to the generator, and gave speeds 

 of from 3,000 to 4,000 revolutions per minute. An 

 alternative method to this was to drive the generator 

 by gearing or belt direct from the main aircraft engine. 

 This latter method was largely used in German aero- 

 planes, but was not adopted to any large extent in 

 British machines, as the wind-driven generator has 

 many advantages over the other. In aircraft the aerial 

 consists of a long length of wire (from about 100 to 

 300 feet according to the wave-length to be used) with 

 a lead weight at one end. During flight this is trailed 

 from the machine and forms an efficient aerial. Before 



landing the wire it wound up on a reel. An aerial of 

 this type is obviously an encumbrance to a fighting 

 machine, and was, in some cases, replaced by a fixed 

 aerial attached permanently to the framework of the 

 aeroplane. The " earth " system is obtained by 

 using the capacity of the engine, bracing wires, and 

 other metal parts in the aircraft. 



One of the main duties of aircraft during war, and 

 one in which wireless plays an important part, is that 

 of observation of artillery fire, or what is commonly 

 called " spotting." In this co-operation between air- 

 craft and artillery wireless is indispensable. In the 

 early days of the war co-operation was attempted by 

 indicating targets by dropping smoke balls or firing 

 coloured signals over them. This method was slow 

 and unsatisfactory, as signals could not be seen very 

 far, and the correction of the ranging by a very limited 

 number of signals was not satisfactory. When 

 wireless apparatus became available, great advances 

 were made, and the success of aerial observation was 

 assured. Large numbers of squadrons of aeroplanes 

 were distributed along the whole front to co-operate 

 with artillery. Pilots and observers were trained in 

 the methods of observing and correcting artillery fire, 

 were taught a little wireless telegraphy and Morse 

 Code to enable them to report targets and maintain 

 communication with artillery units while correcting 

 their fire. Machines for this purpose were mostly 

 equipped with small spark transmitters with an 

 average range of about ten miles. The power of these 

 sets was intentionally kept low to enable as large a 

 number of machines as possible to work on a small 

 sector without interfering with, or being interfered by, 

 similar machines working in neighbouring sectors. 

 Each heavy or siege battery was equipped with a small 

 field set capable of maintaining communication with 

 the aircraft. When a target was observed, a battery 

 was called up by wireless and given the position of 

 the target by means of its co-ordinates on a map 

 ruled in squares. In a few minutes fire was opened 

 on the target, and corrections sent in simple code from 

 the aeroplane to the battery. With practice, gunners 

 and aerial observers soon became very skilled and 

 quick in ranging by this method, and most successful 

 artillery work was achieved. When necessary, more 

 than one battery engaged the target, and trained 

 observers were able to correct the fire of several 

 batteries at the same time. Arrangements also existed 

 whereby, on a certain signal being sent by the aero- 

 plane, the concentrated fire of a large number of 

 batteries could be obtained at once on a target of 

 special importance, such as a body of enemy troops, 

 a railway train, collection of transport, or similar 

 " fleeting target." Wireless has proved its value for 

 work of this nature, and will continue to be necessary 



