24 



NATURE 



[September ii, 1919 



it possible for the scientific worlver to make research 

 his profession (subject, of course, to efficiency), con- 

 crete suggestions regarding methods of achieving this 

 are essential ; and as the committee is a comparatively 

 small body it cannot expect to be acquainted with all 

 the relevant facts concerning the conditions under 

 which research is conducted at present. To overcome 

 this difficulty it is proposed to associate with the com- 

 mittee a number of^advisory panels consisting of per- 

 sons in the principal research centres in the British 

 Isles. Will those workers (whether already members 

 of the Union or not) who would be willing to supply 

 the information required, or to make definite sugges- 

 tions concerning possible methods of improving these 

 conditions, please commimicate with the undersigned 

 or some other member of the committee? 



The present committee consists of the following : — 

 Dr. O. L. Bradv (Chemistry, Imperial College), Dr. 

 J. W. Evans, F.R.S. (Geology, Imperial College), Mr. 

 W. F. Higgins (Experimental Physics, National Physi- 

 cal Laboratory), Dr. A. Holmes (Geology, Imperial 

 College), Dr." H. Jeffreys (Mathematical Physics, 

 Cambridge), Dr. F. Kidd (Plant Physiology, Cam- 

 bridge), Dr. M. C. Ravner (Botany, General Branch), 

 Dr. C. Shearer, F.R.S^ (Zoology, Cambridge), Mr. E. 

 Sinkinson (Chemistry, Imperial College), Dr. C. West 

 (Plant Physiology, 'imperial College), Miss D. M. 

 Winch (Pure Mathematics, Cambridge). 



Harold Jeffreys. 



St. John's College, Cambridge. 



WIRELESS NAVIGATION FOR AIRCRAFT. 



THE determination of the position of ships at 

 sea involves dead reckoning and the use of 

 sights on terrestrial or celestial bodies. Dead 

 reckoning methods often give fairly accurate 

 results, even when no sights can be taken. With 

 aircraft, however, drift plays so large a part that 

 dead reckoning methods are not sufficiently trust- 

 worthy. Hence the necessity for other methods 

 for determining position. 



Directional wireless gives a means of finding 

 one's position under almost any conditions, and 

 thus enables navigation to proceed in cases where 

 it would otherwise be dangerous, such as in fog. It 

 uses chiefly the well-known property of loops, that 

 if the plane of a loop makes an angle with the 

 direction of propagation of the waves, the E.M.F. 

 produced in the loop is Eg cos 6. The rate of 

 variation of this with fi is greatest when ^ = 90°, 

 i.e. when the signal strength is a minimum, and 

 bearings have hitherto been obtained by turning 

 the loop until the minimum is obtained. 



There are two distinct ways in which this navi- 

 gation might be effected : — 



(i) The aircraft should emit ordinary wire- 

 less signals and directional stations on the 

 ground determine various directions of the 

 aircraft, the central ground station working out 

 the position of the aircraft and. re-transmitting it 

 to the aircraft. This method has been used 

 considerably by the Germans. 



(2) There should be ordinary transmitting 

 stations on the ground which should transmit 

 ordinary wireless signals, and the aircraft should 

 determine bearings of each of these known 



NO. 2602, VOL. 104] 



ground stations, the navigator working out his 

 position from these bearings. This method has 

 very many obvious advantages over the first 

 method, such as the fact that an unlimited number 

 of aircraft can work out their own positions at 

 the same time, and also the fact that in case of 

 warfare the position of the aircraft need not be 

 disclosed to the enemy. This second method was 

 adopted in the R.A.F. to a great extent. 



In attempting to place directional gear on air- 

 craft there were considerable difficulties : — (i) 

 There is much extraneous noise on aircraft; (2) 

 the space available on aircraft is not abundant, 

 and in any case it is not easy to get large loops ; 

 (3) the possibility thj^t the waves would be 

 deviated in the neighbourhood of the aircraft, 

 thus producing errors which would have to be 

 determined. 



Fig. I. — A, main aerial ; B, auxiliary aerial. 



It was obvious that the best amplification of 

 signals that could be obtained would have to be 

 used. Even with the best amplification known, 

 it was found that the extraneous noise was so 

 considerable that the ordinary minimum metliod 

 of using a loop aerial to find direction was of very 

 little use. Because of the extraneous noise the 

 minimum was considerably widened, and even 

 with powerful signals there might be a region as 

 large as 40° to 60° where no signals at all were 

 obtained. It was hence necessary to devise some 

 method by which signals could be heard whilst 

 the bearing was taken. For this purpose the 

 following method was devised :■ — 



Two loops at right angles are used. These 

 loops are rigidly fixed together and rotate round 

 the same vertical axis. When one of these loops 

 is on its maximum the other will be on the mini 

 mum. When the maximum or main coil is used 

 alone, the maximum of the signals is first roughly 

 obtained, and then the second or auxiliary coil is 

 introduced, the connections of this second coil 

 being reversed from time to time. If the main 

 coil is on its maximum the reversal of the 

 auxiliary coil will not alter the strength of the 

 signals, but if the main coil is not correctly on 

 the maximum the reversal of the auxiliary coil will 

 give signals of different intensity ; hence the 

 method to employ is to rotate the coils, using the, 

 main coil alone until somewhere near the maxi-«() 



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