INTERFERENCE ON SUBMARINE TELEGRAPH CABLES 407 



turbance can be obtained b\- snnnnation of distnrbances of all fre- 

 quencies. 



The extent l(^ which electrical disturbances penetrate below the 

 surface of the ocean can be determined from the theory of induction of 

 currents in continuous media, where it is shown that the components 

 of the electric {E) and magnetic fields {H) parallel to and at a distance 



< .2 



30 40 50 60 70 



FREQUENCY- CYCLES PER SECOND 



2 below the surtace of an infinite plane conductor are given by the 

 formulas '? 



E = Eo e-^^ H = Ho €-^=, k = 2i:\/2\if, 



(1) 



where Eo and Ho are the values of E and H at the surface, X is the 

 electrical conductivity of the medium and / is the frequency. Em- 

 ploying the value of X for sea water and expressing z in feet, gives 



/^ = 1.3o X 10- V/ (!+*■). 



The cur\-es of Fig. 3, computed from formula (1), indicate the man- 

 ner in which sinusoidal disturbances of frequencies in the telegraph 

 range are attenuated by various depths of sea w^ater. It can be seen 

 that the magnitude of a disturbance falls off rapidly as it penetrates 

 the water; also that this attenuating effect is greater the higher the 

 frequency. At a depth of one or two miles, at which the greater part 



'Jeans "Electricity and Magnetism," 2nd Edition, p. 477. 



