448 



NATURE 



[December i, 192 i 



The Coming: of Age of Long-distance Wireless Telegraphy and some of its Scientific 



Problems.^ 



IT is just twenty-one years since Senatore Marconi 

 began to equip with wireless apparatus a station 

 at Poldliu in Cornwall for the first attempt at trans- 

 atlantic wireless telegraphy. Until then only appli- 

 ances of a laboratory t3^e had been used to signal to 

 distances of about loo miles. This first attempt at 

 long-distance working necessitated the conversion of 

 these appliances into engineering plant employing 

 large power. Although at first the spark system, in 

 which the electric waves are generated by discharges 

 of large electric condensers, was used at Clifden in 

 Ireland and Glace Bay in Nova Scotia, and developed 

 by Senatore Marconi ultimately into the timed spark 

 continuous wave system in the great wireless stations 

 at Carnarvon, N. Wales, New Jersey, U.S.A., and 

 Stavanger, Norway, the usual practice of late years 

 has been to employ either the Poulsen electric arc 

 generator, the high-frequency alternator, or, more 

 recently, the thermionic valve generator. At the re- 

 cently projected gigantic wireless stations, such as 

 those at St. Assise, near Paris, and Long Island, 

 U.S.A., the high-frequency alternators of Latour- 

 Bathenod and of Alexanderson are to be employed. 

 At the first Imperial wireless station at Leafield, 

 Oxfordshire, erected by the General Post Office to 

 correspond with one at Cairo, the Elwell-Poulsen arc 

 generator is used. The arc generator has, however, 

 the disadvantage that the waves emitted are a mixture 

 of wave-lengths, and not a single pure wave or mono- 

 chromatic. Important installations of large valve 

 transmitters have recently been made b}' the Marconi 

 Wireless Telegraph Company at Clifden, Ireland, and 

 at their great Carnarvon station in N. Wales. 



The^length of waves mostly used for long-distance 

 radio work is between 10,000 and 20,000 metres, or 

 about 6 to 12 miles. It is possible from all large radio 

 stations at the present time to communicate with 

 their antipodes. So far as reception is concerned this 

 long-distance working is entirely due to the thermionic 

 valve, the first type of which was invented by Prof. 

 Fleming in 1904. 



It has been proved by the labours of many eminent 



1 Abridged from the fifth Henry Trueman Wood lectuie at the Royal 

 Society of Arts, delivered on Wednesday, November 23, by Prof. J. A. 

 Heming. 



mathematicians during the last twenty years, how- 

 ever, that the received signals at distances of 6000 to 

 12,000 miles are many thousands or even millions of 

 times stronger than can be accounted for by pure 

 diffraction or bending of the waves round the earth, 

 and it is now fairly generally agreed that long-distance 

 wireless telegraphy takes place only in consequence 

 of the existence of an electrical conducting layer in 

 the earth's atmosphere at a height probably of from 

 100 to 200 kilometres. 



The presence of this highly conductive layer in the; 

 upper regions of the atmosphere, in which the com- 

 ponent gases are hydrogen and helium, is probably 

 due to electrified dust which comes to us from the 

 sun being powerfully repelled against the attraction 

 of gravitation by the pressure due to waves of light. 

 This dust comes from the sun with enormous velocity 

 and enters the higher levels of the atmosphere, render- 

 ing it an electric conductor. The conducting layer 

 guides the radio waves round the earth and prevents 

 them from escaping into space. 



In addition, sunlight ionises the subjacent region 

 during the day, but this is removed during the night. 

 Vagrant natural electric waves are always being pro- 

 duced in the atmosphere, and are called "strays";, 

 they are a serious nuisance in radio signalling at cer- 

 tain times, and especially in the tropics. The great 

 outstanding problem of long-distance wireless tele- 

 graphy and telephony is the neutralisation of the effect 

 of these vagrant waves on the receiving apparatus. 



Prof. Fleming concluded with some remarks on the "" 

 bearing on the theory of wireless telegraphy of recent 

 physico-mathematical speculations on relativity, and 

 especially the agnostic view now taken as regards the 

 existence of a space-filling aether. It is clear that 

 space is not a mere vacuum, but has remarkable 

 powers of storing and transmitting energy, but modern 

 physical and astronomical discoveries have rendered' 

 necessary great modification in our ideas regarding the 

 structure of space or. the aether, and no theory of 

 radiation has yet been propounded which explains 

 satisfactorily all the known facts. We are as yet un- 

 able to give any wholly satisfactory explanation as to 

 the nature of the waves used in wireless telegraphy. 



Physical Science at the British Association. 



JUDGING by the continued interest displayed in 

 the meetings of Section A during the recent visit 

 of the British Association to Edinburgh, the pro- 

 ceedings of this section may be accurately described 

 as very successful. Four strenuous mornings were 

 devoted to the formal work of the section, yet the 

 meeting-place was frequently overcrowded, and, even 

 at the very end of the session, the audience num- 

 bered about eighty. There can be no doubt that the 

 policy of the Association in encouraging joint discus- 

 sions between the sections has met with general 

 approval. Section A participated in two of these, both 

 proving of absorbing interest. It is true that the 

 time occupied by the joint meetings put a severe 

 strain upon the rest of the sectional programme, 

 which was undoubtedly too large, consisting of no 

 fewer than twenty-nine items. This led to the neces- 

 sity of adopting the somewhat undesirable practice 

 of splitting up frequently into sub-sections ; and the 

 question of the limitation of the programme in future 

 years is well worthy of consideration. 



NO. 2718, VOL. 108] 



Some new departures were made by Section A at 

 the Edinburgh meeting. The afternoon of the first 

 day was made the occasion for demonstrations of 

 novel physical experiments in the laboratories of the 

 Natural Philosophy Department, where also apparatus 

 of historical interest was exhibited. A semi-popular 

 lecture was delivered on another alternoon. Both 

 these new activities of the section met with great 

 success, and ought certainly to be repeated at sub- 

 sequent meetings. It may be hoped, too, that the 

 excellent arrangements for producing a daily weather 

 report (referred to later) will become a normal part of 

 the work of Section A. 



From remarks made earlier in reference to the 

 lengthy programme, it will be understood that in the 

 present report little more can be done than give a list 

 of the pap>ers and authors, with the addition of a 

 few descriptive remarks in cases of outstanding 

 interest. The proceedings opened on the morning of 

 September 8 with a paper by Prof. J. C. McLennan 

 on " Radiation and Absorption by Atoms with 



