198 



PIERCE. 



6. Field Due to a Doublet at P'. — At a distant point P the 

 electric and magnetic intensities due to a doublet of length dz' and 

 charges e and —eaXP' is, by Hertz's theory, 



dEe = dH^ = -^— f (t — r/c), 



(10) 



where 



m 



dEe 



dR4> 



r 

 c 



the moment of the doublet 



e dz', (11) 



the electric intensity in electrostatic units, which is en- 

 tirely in the direction oid; that is, of the meridional lines; 

 the magnetic intensity in electromagnetic units, which is 

 entirely in the direction of the parallels of latitude, 

 distance P'P in centimeters, 

 velocity of light in centimeters per second. 



The two dots over the /in (10) indicate the second time derivative. 



In writing equation (10), the slight difference in the direction of 



the perpendicular to r from the direction of the perpendicular to ro 



Figure 4. 



is neglected in view of the largeness of ro in comparison with the length 

 z' measured on the antenna. 



Also the r which should occur in the denominator of (10) has been 



