IN THE FIELD ROUND A THEORETICAL HERTZIAN OBCILLAT' 187 



Tin- LfiH-nil \.-ilin- I'.T ( ./. :;! \iiiL: tin- |". In! ..f nro I.II.-IM-. i- Ocfi 8*748,707 

 -f -112,193 Co, approximately. For our special case, Od = 2'9079. 



It will be seen that our curve approaches closer to its asymptote than the curve for 

 the true wave of transverse vibrations. Further, the centre, d, from which the wave 

 with positive velocity may be supposed to start, is moved far further from the origin. 

 It is rather further from the origin than it would be in the case of an undamped 

 train.* There seems, therefore, considerable doubt as to what HKHTX was really 

 measuring in the case of his interference experiments in the equatorial plane. Was he 

 it ally measuring IV., or possibly I., obscured in its effect by the superposition of II. '. 

 It is, we think, needful to re-examine the whole matter physically, endeavouring to 

 distinguish tatween the components <, and fa. For this purpose the direction of the 

 axis, rather than the plane of the equator, seems the more suitable for experiment. 

 For in this direction the magnetic induction and the transverse electric component 

 wave disappear, and we have the axial component electric wave only to deal with, 

 i.e., II. only, I. and III. being not extant. 



Further, the numerous theoretical singular points to which we have referred seem 

 to deserve, if possible, physical investigation. To do this we require to emphasise as 

 much as possible their distance from the oscillator. But this means that we must 

 get from a small oscillator a long wave-length, if the rate of damping (^) be fixed, 

 or, if the wave-length be fixed, we require very rapid damping. Neither of these 

 conditions seem easy of physical realisation. Still something might be done by way 

 of striking a balance, and, at any rate, we must not disregard the fact that a con- 

 siderable portion of HERTZ'S experiments were made inside that portion of the field 

 where the influence of these singular points and of the damping should at least 

 theoretically make themselves felt. 



(14.) Concluifions. We may draw the following general conclusions : 



(i.) The effect of damping makes itself very sensible in modifying the form of the 



wave -surface as propagated into space from a theoretical oscillator. The typical 



Hertzian wave-diagrams require to be replaced by the fuller series accompanying this 



memoir. 



(ii.) Three waves of electro-magnetic force may be considered as sent out from the 



oscillator, and these waves we believe capable of physical identification. 



First, a component wave of transverse electric force, determined by <,. This also 

 gives the wave-speed and phase of force perpendicular to the oscillator axis. 



Secondly, a component wave of electric force parallel to the axis, determined by 

 < 2 . This also gives the wave-speed and phase of force radial to tin- 

 oscillator. 



Thirdly, a wave of magnetic force. 



* In this case Od = 2-743,707 correct to the last place. In the general approximate value given above, 

 we have neglected terms of the order x'i and the approximation is not nearly as accurate as this. 



2 B 2 



