128 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1911, 
the atmosphere, which, on account of their doubtful origin, have been 
called “ X’s.” 
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 
ask or ae before the probable effect of the 
Beye se fois conductivity of the earth was con- 
nose Lens tx. sidered and discussed. 
Lord Rayleigh, in referring to 
transatlantic radiotelegraphy, 
stated in a paper read before the 
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.' 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 omiatien from a classical Hertzian oscillator, but instead 
glide along the surface of the earth. 
Prof. Zenneck? 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 
1 Proc. Roy. Soc., vol. 72, p. 40. 
2Annalen der Physik,’’ vol. 23, p. 846, ‘ Physikalische Zeitschrift,”’ 1908, pp. 50, 553 
