September ii, 1919] 



NATURE 



25 



mum, and then to introduce the auxiliary coil, 

 making the final adjustment so that on re- 

 versing the auxiliary coil there is no change in 

 the intensity of the signals. The sensitiveness 

 that can be obtained by this method is under 

 control and depends on the ratio of the area turns 

 of the auxiliary and the main coils. By " area 

 turns " is meant the summation of the areas of 

 the various turns of a loop. If this ratio is of 

 the order of 3 to i, a bearing can be determined 

 quite easily to within i°. If this ratio 

 is 10 to I, the coils are accurate to less than :^°. 

 It is quite simple to show the reason for this 

 theoretically. There are two distinct methods of 

 applying this method to aeroplanes : — 



(i) The coils are rigidly attached to the 

 aeroplane and the aeroplane rotated until 

 the correct bearing is obtained. This is 

 called the wing coil system. The main 

 coil is fixed in the fore-and-aft direction 

 on the struts and the wings. The auxi- 

 liary coil is athwart-ships on the struts 

 and the wings. Fig. i shows diagram- 

 matically how this is done. 



(2) The coils are placed in the fuselage 

 of the machine and are rotated inde- 

 pendently of the machine. Method (i) 

 has the advantage that stronger signals 

 are obtained and can hence be used for 

 long distances, such as for the cross- 

 Atlantic flight. This method has the dis- 

 advantage that it is necessary to deviate 

 the machine from its course to determine 

 any bearing. It has also the advantage 

 that there are no errors due to the devia- 

 tion of waves. 



Method (2) has the advantage that the 

 machine can carry on on a steady course 

 whilst bearings are being taken. It has, 

 however, disadvantages that signals are 

 much weaker and that errors are intro- 

 duced in the bearings. Such errors are 

 quadrantal in nature and can be deter- 

 mined by swinging the machine and 

 taking bearings on the same station for 

 different directions of the head of the 

 machine. 



On aeroplanes the extraneous noise 

 can be divided into two distinct 

 classes : (i) The noise of the engine 

 and the rushing of the wind ; (2} the disturbance 

 produced by the magneto. 



The noise of the engines can be minimised by 

 increasing the amplification of signals, but 

 magneto noise cannot be eliminated in such a way 

 because, as the amplification is increased, the 

 effect of the magneto disturbance also increases. 

 It was absolutely necessary to determine methods 

 to cut out this magneto disturbance. It was 

 found that the magneto disturbance was prin- 

 cipally due to the emission of very short waves of 

 the order of 5 to 30 metres. The most effective 

 method for cutting out these disturbances was 

 completely to shield the magneto system. The 



no; 26o2_, vol. 104] 



magneto leads were made of braided wire, the 

 braiding being earthed every 18 or 24 in. It 

 was also necessary in cases where the engine is 

 not completely cowled to enclose the magnetos 

 and their distributors in metal shields. 



A large number of results of determinations of 

 {XDsition by wireless bearings have been obtained. 

 The beac!t)n stations used were principally long- 

 wave spark stations (wave-lengths of 2000 metres 

 and upwards), the distances of the beacons being 

 from 10 to 500 miles, and occasionally more 

 distant. Some of the stations used were Poldhu, 

 Paris, and Nauen. 



On the ground, when two or more of these 



Fig. 2. — Outward journey. Dotted line, thus — •■ — •• — indicates actual track of 

 machine as followed by map reader. 



beacons were used, the mean error in the deter- 

 mination of position was two miles. In aero- 

 planes the accuracy was not so good owing to the 

 compass errors, due to the swinging of the com- 

 pass. The mean error in bearing in the air was 

 i|°, and the mean error in position when two or 

 more beacons were used was seven miles. 



Long-distance flights have been made in which, 

 under adverse weather conditions and without 

 reference to the ground, by the sole use of 

 directional wireless the machine was navigated 

 with extraordinary accuracy. The details of a 

 flight from Biggin Hill to Paris and back to 

 Brighton are shown in Figs. 2 and 3. The aero- 



