Theory of Electricity . 435 



motion induced by the continuous primary current. Again, the 

 recoil of the impulse induced in the secondary coil by the ter- 

 minal extra-current in the primary (the terminal induced current), 

 will likewise be in a direction contrary to that of the inducing 

 impulse, but its potential will remain undiminished, as it is un- 

 opposed by any continuous induction; and it will therefore 

 possess greater force than the initial induced current. 



But it may be asked by those who find a difficulty in dis- 

 possessing their minds of long-established and time-honoured 

 notions, Is not all this about "inertia" and " vis viva" and 

 " impulses " sheer hypothesis ? Not so : the writer has long 

 since observed and recorded a precisely similar phenomenon (ap- 

 parently an exact analogue of the initial extra- current) in an 

 unquestioned case of wave-motion — an experiment on the inter- 

 ference of sound-waves, due in common with so many others to 

 the genius of Prof. Wheatstone. Let the handle of a vibrating 

 tuning-fork, held obliquely, rest on the surface of a table : as 

 long as it remains at rest, a loud resonance of the table is 

 audible ; but if the tuning-fork be moved parallel to itself along 

 the surface of the table in any direction, the resonance of the 

 table immediately ceases, from the perpetual interference of the 

 vibrations in successive parallel planes with each other. The 

 instant the tuning-fork stops, the resonance bursts out again 

 in a very striking manner. If the tuning-fork be held verti- 

 cally, the planes of vibration coincide, and the resonance is not 

 interrupted by moving it. It can scarcely be doubted that the 

 impulsive recommencement of the resonance, after its interrup- 

 tion by interference, is entirely due to the dynamical cause 

 here assigned to the initial extra-current. 



M. Chauveau (no doubt correctly) ascribes the physiological 

 effect of an electric impulse to the dynamical molecular disturb- 

 ance w r hich it produces. 



It will naturally be asked if electricity be only w r ave-motion, 

 what is the nature of that motion, and in what respects does it 

 differ from the wave-motion of light and heat ? It is evident 

 that the existence of two opposite electrical states must involve 

 some kind of polarity or directionality in the motion, not re- 

 quired to explain the phenomena of light and heat. The pro- 

 bable dependence of magnetism on the circulation of electricity 

 round the molecules of the magnet would seem to suggest the 

 idea of circular waves ; and if these be supposed analogous to 

 the waves of circularly polarized light, the phenomena of 

 electric polarity may be readily explained. Moreover the state 

 of mutual inductive constraint of the electricity of two opposed 

 and oppositely electrified surfaces may be roughly symbolized by 

 the condition of two spiral springs, mutually compressing each 

 other against an intervening obstacle. 



2F2 



