308 



DISCOYliHY 



in warfare as the best means of communication between 

 aircraft and artillery, for with modern long-range guns 

 correct observation of the fall of rounds is only possible 

 from an observer hovering over the target. In future, 

 wireless telegraphy may be replaced by wireless tele- 

 phony for this purpose ; this would allow more inti- 

 mate communication between the observer and the 

 battery commander. Apart from this there would 

 appear to be no very great advantage in using telephony 

 instead of telegraphy for the purpose. 



A second important use to which wireless in aircraft 

 was largely put during the war was in connection with 

 long-range reconnaissance flights and bombing expedi- 

 tions. In carrying out duties of this nature, aircraft 

 flew many miles beyond the enemy front line, and 

 obtained " intelligence " in the course of a three or 

 more hours' flight which it was often essential to 

 report at once without waiting till the whole flight was 

 completed. For example, movements of enemy 

 troops behind the line, concentrations of transport or 

 rolling stock, lighted enemy aerodromes seen during 

 night-flights, good bombing targets, etc., were matters 

 of strategic importance of which immediate knowledge 

 was necessary if action was to be taken in time ; this 

 information was best sent during flight by wireless to 

 certain land stations erected for the purpose at suit- 

 able headquarters. The supreme importance of rapid 

 communication in reporting enemy movements and 

 dispositions is more fully realised under moving-battle 

 conditions during a large advance or retreat such as 

 took place in the initial and final stages of the war in 

 France, and also in the final phases of the campaign 

 in Palestine. Aircraft engaged on long-range recon- 

 naissance and bombing duties were first equipped with 

 long-range spark transmitters capable of maintaining 

 efficient communication up to about 50 to 100 miles, 

 or more if necessary. Later, after the development 

 of the Three Electrode Oscillation-Valve, • and its 

 adaptation for use in aircraft sets, these spark trans- 

 mitters were replaced by continuous-wave transmitters 

 giving much longer ranges for less power. These con- 

 tinuous-wave transmitters have many advantages over 

 the older spark types, and are eminently suited in all 

 respects for use in aircraft. 



The next development to take place in aircraft 

 wireless was in the use of wireless telephony. To the 

 non-technical reader one may say that wireless tele- 

 graphy differs from wireless telephony just as ordinary 

 telegraphy differs from ordinary telephony — in the 

 one a code of dots and dashes is used to transmit the 

 message, while in the other the message is transmitted 

 as in ordinary spoken conversation. Wireless tele- 



' This is described fully in recent textbooks on wireless, 

 and also simply in the article on wireless by Lieut. -Col. Crawley 

 in the July issue of Discovery. 



phony demonstrations had been given between land 

 stations before the war, but wireless speech had never 

 been received in an aeroplane. The whole of this 

 momentous development in aircraft wireless telephony 

 has taken place during the years of war. and has been 

 the result of long and patient industrious research and 

 experiment on the part of a few able pioneers. The 

 difficulties to be surmounted were tremendous. Tele- 

 phone conversation on the ground is often not all that 

 one could desire, but when this has to be undertaken 

 in an aeroplane rusliing through the air at about a 

 hundred miles an hour, and amid the continuous roar of 

 a high-power aeroplane engine so deafening that an 

 observer can only hear his pilot's shouted words when 

 the latter 's mouth is close to his ear, one can, to a small 

 extent, appreciate some of the difficulties to be over- 

 come. By the perfection of a transmitter-microphone 

 insensible to loud noises such as those of the engine, 

 yet responsive to the modulations of the himian 

 voice, and by the use of high-magnification valve 

 arrangements, satisfactory' results were at length 

 obtained, and a standard type of instrument was 

 designed and manufactured which necessitated practi- 

 cally no adjustments in the air. With such sets, 

 pilots and observers no longer required to learn the 

 Morse Code and wireless signal procedure ; this alone 

 was a great benefit, and, moreover, considerable time 

 was saved in the transmission of messages. Not 

 only were aircraft able to maintain speech communica- 

 tion between themselves and the ground, but they 

 were able to hold conversation with other aircraft in 

 flight. This was of great value in " formation fl\ing," 

 when a number of aeroplanes fly in a body under the 

 leadership of a commander who, by this means, can 

 give directions and orders to the members of his for- 

 mation and also maintain communication with the 

 ground. For fighting purposes in the air this has 

 obvious advantages ; its value, too, was proved by 

 its use in the squadrons employed in the defence of 

 London, as machines on patrol duty in the air could 

 be easily kept informed of the approach or morement 

 of enemy aeroplanes or airships. 



Before dealing with the latest development- - namely, 

 aircraft direction-finding wireless — it will be advisable 

 to consider briefly and in the simplest possible terms 

 the main principle involved in directional wireless as 

 applied to aircraft. 



If, while an operator at receiving station A (Fig. i) 

 listens to wireless signals sent with uniform power 

 from a fixed station B, the receiving aerial AC be 

 rotated about A, the strength of the received signals 

 will be found to vary in intensity : the signals heard 

 will be loudest when the receiving aerial hes in the 

 straight line joining AB, as shown in the diagram. Now, 

 orienting the aerial of a wireless station is no small 



