128 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1911. 



the atmosphere, which, on account of their doubtful origin, have been 

 called "XV 



Although the mathematical theory of electric wave propagation 

 through space was worked out by Clerk Maxwell more than 50 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 con- 

 cerning the manner of propagation of the waves on which wireless 

 telegraph transmission is based. For example, in the early days of 

 wireless telegraphy it was generally believed that the curvature of 

 the earth would constitute an insurmountable obstacle to the trans- 

 mission of electric waves between widely separated points. For a 

 considerable time not sufficient account was taken of the probable 

 effect of the earth connection, especially in regard to the transmission 

 of oscillations over long distances. 



Physicists seemed to consider for a long time that wireless teleg- 

 raphy 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 con- 



// .••;'-.. / \ .•— !\ v. sidered and discussed. 



W ''-r-. I': •'£--$£•$•. \\ r\'\'' \'' Lord Rayleigh, in referring to 



^JjMl^MtMlJ^2l%^^U)L^. transatlantic radiotelegraphy, 



^■' stated in a paper read before the 



FlQM - Royal Society in May, 1903, that 



the results which I had obtained in signaling 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. 1 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 semiloops of electric strain from a simple vertical 



wire (fig. 11). 



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 2 has carefully examined the effect of earthed receiv- 

 ing and transmitting aerials, and has endeavored to show mathe- 

 matically 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 



i Proc. Roy. Soc, vol. 72, p. 40. 



»"Annalen der Physik," vol. 23, p. 846, " Physikalische Zeitschrift," 1908, pp. 50, 553. 



