March 7, 1889] 



NA TURE 



451 



the distance given in the figure as \K for the lime \T. At in- 

 finitesimal distance from the origin the velocity of outspreading 

 is indeed infinite. 



This phenomenon it is which we represented in the old mode of 

 expression by saying that along with the inductive action travel- 

 ling with the velocity of light there was superposed an electrostatic 

 force travelling with infinite speeJ. 



We properly express this phenomenon in terms of our present 

 theory when we remark that fundamentally the self-forming waves 

 do not arise solely from processes occurring ai the origin, but are 

 influenced by the condition of the whole surrounding medium, 

 which latter, according to Maxwell's theory, is the true seat of the 

 energy. However this may be, the surface Q -^ o expands with 



velocity which gradually reduces to 



and by the time 



/ = ^T it fills the space R, (Fig. 3). By this time the electro- 

 static charging of the pole is at its greatest development ; the 

 number of lines of force which start thence attains its maximunv 

 value. 



With further increase of time no fresh lines of force protrude 

 from the poles ; rather, those already produced begin to withdraw ■ 

 back into the conductor, there to vanish as lines of electric force, 

 their energy, however, being converted into magnetic energy. 



Hence occurs a singular behaviour which in Fig. 4 (/ = ^T) 

 is plainly to be recognized, at least in its beginning. The hnes 

 which have furthest removed themselves from the origin get 



Pig. 1 



Theic figure* c'>rrespond 1 1 succe5>ive stages in the history of a semi-oscillation. Ignsring the arrows. Fig. i represents the state of things at the end of 

 •■very half-penod ; Fig. 3 at the end of every quarter-period ; Figs. ■>. and 4 represent one-eighth and three-eighths of a complete oscillation respectively. 

 I do not feel clear about the correctness of the straight arrows in Fig. 1. 



drawn together by the stress with a lateral inflexion ; this in- 

 flexion approaches nearer and nearer to the axis of s ; and then 

 a self-closed ponion detaches itself from each of the outer lines 

 of force, which automatically spread out into space, while the 

 residue sink back into the conductor. 



The number of receding lines is just as great as the number 

 iriginally expanding lines; their energy, however, is neces- 



ily diminished by the energy of the detached portion. 



ii lo s of energy corresponds to the radiation into space. 



consequence of it the oscillation must soon come to rest un- 

 some impressed forces restore the energy lost to the source. 

 ^\ieanwhile we have regarded the oscillations as undamped, 

 and thus implicitly understood the existence of such forces. 



In Fig. I, to which we can now return for the time / = T, 

 since we can imagine the arrows inverted, the detached 

 portions of the lines of force fill the s]iace Rj, while the lines 

 starting from the poles have completely vanished. But new 

 lines of force break out from the pole, and compress the lines 



I whose early history we have followed into the space R5 



! (Fig. 2). 



It needs no further explanation now to follow these lines into the 

 spaces Rg. R,, and R^. More and more they transform them- 



'\ selves into a pure transverse wave motion, and lose themselves 

 as such in the distance. One would get the be-t picture of the 



! ))lay of force if one made a series of drawings for still smaller 



I time-intervals, and examined them with a stroboscopic disk. 



