420 Professor Oliver Lodge [March 8, 



reasonable distance if both are tuned to the same note. Everyone 

 knows, also, that a fork can throw a stretched string attached to it 

 into sympathetic vibration if the two are tuned to unison or to some 

 simple harmonic. Both these facts have their electrical analogue. I 

 have not time to go fully into the matter to-night, but I may just 

 mention the two cases which I have myself specially noticed. 



A Leyden jar discharge can so excite a similarly-timed neigh- 

 bouring Leyden jar circuit as to cause the latter to burst its dielectric 

 if thin and weak enough. The well-timed impulses accumulate in 

 the neighbouring circuit till they break through a quite perceptible 

 thickness of air. 



Put the circuits out of unison by varying the capacity or by 

 including a longer wire in one of them ; then, although the added 

 wire be a coil of several turns, well adapted to assist mutual induc- 

 tion as ordinarily understood, the effect will no longer occur, 

 until the capacity is suitably diminished and the synchronism 

 thus restored. 



That is one case, and it is the electrical analogue of one tuning- 

 fork exciting another. It is too small at present to show here 

 satisfactorily, for I only recently observed it, but it is exhibited in 

 the library at the back. 



The other case, analogous to the excitation of a stretched string 

 of proper length by a tuning-fork, I published last year under the 

 name of the experiment of the recoil kick, where a Leyden jar circuit 

 sends waves along a wire connected by one end with it, which waves 

 splash off at the far end with an electric brush or long spark. 



I will show merely one phase of it to-night, and that is the 

 reaction of the impulse accumulated in the wire upon the jar itself, 

 causing it to either overflow or burst. (Sparks of gallon or jDint jar 

 made to overflow by wire round room.*) 



The early observations by Franklin on the bursting of Leyden 

 jars, and the extraordinary complexity or multiplicity of the fracture 

 that often results, are most interesting. His electric experiments as 



* During the course of this experiment, tlie gilt paper on tlie wall was 

 observed by tlie audience to be sparkling, every gilt patch over a certain area 

 discharging into the next, after the manner of a spangled jar. It was probably 

 due to some kind of sympathetic resonance. Electricity splashes about in con- 

 ductors iu a surprising way everywhere in the neighbourhood of a discharge. 

 For instance, a telescope in the hand of one of the audience was reported 

 afterwards to be giving off little sparks at every discharge of the jar. Every- 

 thing which happens to have a period of electric oscillation corresponding to 

 some harmonic of the main oscillation of a discharge is liable to behave in this 

 way. When light falls on an opaque surface it turns into some other form of 

 energy. What the audience s:iw was probably the result of waves of electrical 

 radiation being quenched or reflected by the walls of the room, and generating 

 electrical currents in the act. It is these electric surgings which render such 

 severe caution necessary in the erection of lightning-conductors. 



This explanation is merely tentative. I have had no time to investigate 

 the matter locally. 



