17* PfcOFESSOJi K. 1'KAkSON AND MISS A. LKK ON THK VIMKATloNs 



lost in his theory. We may consider these to be two separate waves travelling in 

 the equatorial plane, both indeed transverse just for this plane, hut one <, travelling 

 \\itli the velocity of the transverse component electric wave and the other with the 

 velocity of the magnetic wave, or that of the wave of axial component electric force. 

 Thus HKKTZ'S original explanation of the irregularity of the interferences which did 

 not succeed -each other at equal distances, hut with more rapid changes in the 

 neighbourhood of the oscillator, seems justified by the fuller theory. Namely, he 

 explained this behaviour by the supposition " that the total force might be split up 

 into two parts, of which the one, the electromagnetic, was propagated with the 

 velocity of light, while the other, the electrostatic, was propagated with greater and 

 perhaps infinite velocity." Actually we may resolve into two waves; the transverse 

 component electric wave is propagated with greater velocity than the wave of axial 

 component electric force, which has the velocity of the magnetic wave. Many of 

 HERTZ'S experiments were made at a comparatively short distance from the oscillator, 

 and some of the discrepancies he noted between his theory and experiment seem 

 capable of explanation by aid of the velocity diagram given above. 



(10.) There is another quantity which HERTZ considers at length, namely, the rate 

 of change of the magnetic force, which gives the integral force of induction round a 

 small circle in a plane perpendicular to the magnetic force. We shall now accordingly 

 consider the expression for dP/dt from (xvii) : 



~ 



= P (r) sin 9 



cos 



U- - - 

 \ ^ T 



where & = &> + x an( * therefore from (xix), 



cot (& - 2 x ) = - tan x . 

 A more convenient form is easily deduced, namely : 



tan &-3 = 



... (xxxvii), 



where r, = sin ^ as before. 



