I 22 



NA TURE 



[July 28, 1923 



and as the originator of " carrier " waves, rendering 

 possible multiple telephony. 



For the application of the valve as a rectifier of 

 electric currents, we have to thank P'leming himself, 

 while its whole action depends on the properties of 

 the electron and the discoveries of J. J. Thomson. 

 By the use of the valve as a repeater, many ingenious 

 relays, the outcome of long and difficult investigations, 

 have been placed in a secondary position ; the lecturer 

 explains in some detail how, by the selection of the 

 suitable part of its characteristic curve, variations in 

 the grid voltage can be impressed on the plate current 

 and amplified by a transformer, while if another 

 portion of the characteristic be employed, carrier wave 

 multiple telephony is realised. In this " frequency 

 filters " are employed — short circuits containing capacity 

 and inductance which allow only those currents in 

 which the frequency lies between certain limits to 

 enter the line. The broad principles of the method 

 are outlined thus : 



" At one end of an existing long-distance telephone 

 line used in the ordinary way for telephonic speech 

 we can attach a certain number of modulating valves 

 with their plate circuits coupled to the line with 

 their appropriate transformers and filters. We can 

 then generate by means of a number of oscillating 

 valves high frequency currents of certain different 

 frequencies and apply the electromotive forces due 

 to these in series with the electromotive forces of 

 low or speech frequency produced by ordinary'' carbon 

 microphone transmitters so ais to give to the grids 

 of the several modulating valves carrier frequency 

 plus voice frequency voltages. At the receiving end 

 we separate out the several groups of oscillations by 

 suitable band filters and apply the electromotive 

 forces produced by suitable transformers to the grids 

 of demodulating valves. In the plate circuits of these 

 last valves we have coupled ordinary telephone 

 receivers actuated by the voice currents disentangled 

 by these demodulating valves from their respective 

 carrier circuits." 



Such has been the progress of less than fifty years. 

 Fleming asks somewhat despondingly what is being 

 done now in Great Britain. He refers to the labora- 

 tories of the great technical corporations of the United 

 States, the American Telephone and Telegraph Com 

 pany, the Western Electric Company, and the General 

 Electric Company, giving an account of their activities 

 in almost the same terms as those employed by Sir 

 J. J. Thomson in his address to the Institute of Physics. 

 *' They retain," he writes, " the services of scientific 

 investigators of the highest ability, who direct their 

 attention not exclusively to problems of immediate 

 commercial advantage, but look' far ahead into the 

 possible requirements of the future." Sir J. J. 

 Thomson described two of these laboratories as seen 

 by him during his recent visit to the United States. 



NO. 2804, VOL. 112] 



He found men at work on the most abstruse questions 

 of physics — one need only mention Langmuir and the 

 properties of the atom, or Coolidge and the investiga- 

 tions which led to the development of the Coolidge 

 tube. There were numerous staffs of skilled assistants, 

 some no doubt engaged in solving conundrums put 

 to them by puzzled works managers, but many others 

 searching deep into the secrets of Nature in the 

 endeavour to find out new truths and to advance 

 natural knowledge. Funds were practically unstinted, 

 for the business directors of the works had found 

 that by this means only could they extend the sphere 

 of their activities and provide the dividends called 

 for by their shareholders. In the United States 

 abstract science has been made to pay. 



Or to turn to another subject and another speaker. 

 Quite recently the Wilbur Wright lecture, established 

 by the Royal Aeronautical Society in memory of the 

 American pioneer of aviation, was delivered in London 

 by Prof. Ames, of the Johns Hopkins University. 

 Prof. Ames is the chairman of the Executive Com- 

 mittee of the National Advisory Committee for 

 Aeronautics of the United States, and directs the 

 experimental work — full scale and model — of that 

 committee at Langley Field. He has realised very 

 fully the importance of an accurate knowledge of 

 the air pressures on any part of aircraft undergoing 

 manoeuvres in the air ; we were well aware of this, 

 and years ago had done model experiments at the 

 National Physical Laboratory, while at Famborough 

 apparatus for use in the air had been devised and some 

 few experiments made. Prof. Ames showed slides illus- 

 trating in a most striking way the results obtained both 

 on aeroplanes and airships, leading to information in 

 the case of the latter which the Aeronautical Research 

 Committee has pressed for many times, and which, 

 had it been available in time, should have prevented 

 the accident to the British airship R38. 



Nor is this all : instruments have been successfully 

 constructed which permit all the elements which 

 contribute to a knowledge of the flight of an aeroplane — 

 its velocities, accelerations, and the stresses to which 

 its various parts are subject in the air — ^to be recorded 

 during its flight. Instruments corresponding to some 

 of these, such as the quartz-fibre accelerometer or 

 the control force measuring stick, have been in existence 

 at the Royal Aircraft Establishment for years ; instru- 

 ments corresponding to all have been planned and are 

 in various stages of construction. In the United States 

 they have found a man gifted with the knowledge to 

 realise their need and with the authority to give effect 

 to his knowledge. In England we have lagged behind. 

 So it is in other subjects ; Great Britain is a small 

 country, it is true, compared with the United States. 



