6o4 



NATURE 



[June 29, 191 1 



Italian Government between a station situated at Massaua 

 in East Africa and Coltano in Italy. Considerable interest 

 attached to these experiments in view of the fact that 

 the line connecting the two stations passes over exceed- 

 ingly dry country and across vast stretches of desert, 

 including parts of Abyssinia, the Sudan, and the Libyan 



Fig. II. r 



Desert. The distance between the two stations is about 

 2600 miles. 



The wave-length of the sending station in Africa was 

 too small to allow of transmission being effected during 

 daytime, but the results obtained during the hours of 

 darkness were exceedingly good, the received signals being 

 quite steady and readable. 



The improvements introduced at Clifden 

 and Glace Bay have had the result of 

 greatly minimising the interference to 

 which wireless transmission over long 

 distances was particularly exposed in tht^ 

 early days. 



The signals arriving at Clifden from 

 Canada are, as a rule, easily read through 

 any ordinary electrical atmospheric disturb- 

 ance. This strengthening of the received 

 signals has, moreover, made possible the 

 use of recording instruments which not 

 only give a fixed record of the received 

 messages, but are also capable of being 

 operated at a much higher rate of speed 

 than could ever be obtained by means of an 

 operator reading by sound or sight. The 

 record of the signals is obtained by means 

 of photography in the following manner. 

 A sensitive Einthoven string galvanometer 

 is connected to the magnetic detector or 

 valve receiver, and the deflections of its filament caused by 

 the incoming signals are projected and photographically 

 fixed on a sensitive strip, which is moved along at a suit- 

 able speed (Fig. 12). On some of these records, which I 

 am able to show, it is interesting to note the characteristic 

 marks and signs produced amongst the signals by natural 



electric waves or other electrical disturbances of the armo- 

 sphere, which, on account of their doubtful origin, have 

 been called " X's." 



Although the mathematical theory of electric wave pro- 

 pagation through space was worked out by Clerk Maxwell 

 more than fifty years ago, and notwithstanding all the 

 experimental evidence obtained in laboratories concerning 

 the nature of these waves, yet, so far, we understand but 

 incompletely the true fundamental principles concerning 

 the manner of propagation of the waves on which wireles' 

 telegraph transmission is based. For example, in the 

 early days of wireless telegraphy it was generally believea 

 that the curvature of the earth would constitute an in 

 surmountable obstacle to the transmission of electric wave^ 

 between widely separated jx>ints. For a considerable tim- 

 not sufficient account was taken of the probable effect 

 the earth connection, especially in regard to the trans 

 mission of oscillations over long distances. 



Physicists seemed to consider for a long time that wire 

 less telegraphy was solely dependent on the effects of free 

 Hertzian radiation through space, and it was years before 

 the probable effect of the conductivity of the earth was 

 considered and discussed. 



Lord Rayleigh, in referring to Transatlantic radio- 

 telegraphy, stated in a paper read before the Royal Society 

 in May, 1903, that the results which I had obtained in 

 signalling across the Atlantic suggested " a more decided 

 bending or diffraction of the waves round the protuberant 

 earth than had been expected," and, further, said that it 

 imparted a great interest to the theoretical problem.' 

 Prof. Fleming in his book on electric-wave telegraphy 

 gives diagrams showing what may be taken to be a 

 diagrammatic representation of the detachment of semi- 

 loops of electric strain from a simple vertical wire 



(Fig- 13)- 



As will be seen, these waves do not propagate in the 

 same manner as does free radiation from a classical 

 Hertzian oscillator, but instead glide along the surface of 

 the earth. 



Prof. Zenneck ^ has carefully examined the effect of 

 earthed receiving and transmitting aerials, and has 

 endeavoured to show mathematically that when the lines 

 of electrical force, constituting a wave front, pass along 

 a surface of low specific inductive capacity — such as the 

 earth — they become inclined forward, their lower ends 

 being retarded by the resistance of the conductor to which 

 they are attached. It therefore would seem that wireless 

 telegraphy as at present practised is, to some extent at 

 least, dependent on the conductivity of the earth, and that 

 the difference in operation across long distances of sea 

 compared to over land is sufficiently explained by the fact 

 that sea water is a much better conductor than is land. 



The importance or utility of the earth connection has 

 been sometimes questioned, but in my opinion no practical 



Fig. 12. 



system of wireless telegraphy exists where the instruments 

 are not in some manner connected to earth. By connec- 

 tion to earth I do not necessarily mean an ordinary 



- Proceedinii'; of the Roy^I Society, vol. Ixxi-., May 28, 1C03. 

 2 See J. Zenneck. Annalcn tier P'lysik, 23. 5. p. 846, feptember, 1908. 

 Pkysikal Zeitschrift, No. a, p. 50 ; No. 17, p. 553. 



NO. 2174, VOL. 86] 



