1867.] 



of Electric Energy. 



409 



direction on the table, the resonance ceases, from the perpetual interference 

 of the successive planes of vibration with each other. But now comes the 

 illustration : — On arresting the motion of translation, the resonance imme- 

 diately recommences, but with a rush or momentary increase of sound : 

 this must unquestionably arise from the resistance offered by the inertia 

 of the molecules of wood to the recommencement of wave-motion ; and the 

 parallel phenomenon in electricity may undoubtedly be similarly accounted 

 for. And the reflex momentary current (the terminal extra-current of 

 Faraday), which is well known to take place at the instant of opening the 

 circuit, is equally susceptible of a dynamic interpretation : it is the ana- 

 logue of the wave reflected from the fixed end of a stretched cord, after 

 having been imparted by the hand to the free end. 



The dynamic nature of electric energy is clearly indicated by the dy- 

 namo-electric* machine of Holtz, in which dynamic is directly converted 

 into electric energy, — and by the cognate machines of Wilde, Wheatstone, 

 Siemens, and Ladd, in all of which alike there is an intervening conver- 

 sion of dynamic into magnetic energy. The enormous amount of current- 

 energy evolved in Mr. Wilde's machine when the power of a steam-engine 

 is employed to rotate the armatures may be judged of by the fact that a 

 long piece of platinum wire 0*2 inch in thickness was seen to be disinte- 

 grated and partially fused. It is difficult to conceive that in these 

 instances dynamic energy can be converted into magnetic " fluid," and 

 that again into thermic energy ; the conversion of motion into matter, 

 and the subsequent reconversion of matter into motion, are obviously im- 

 possible. 



Some further consideration of the effects of electric energy may serve 

 to indicate the probable nature of the wave-motion. The facts of electric 

 and magnetic polarity imply and necessitate a polarity or directionality in 

 the motion itself, which has no analogue in the waves of sound, light, or 

 heat. This requirement is fully met by the hypothesis of a circular spiral 

 wave, the motion of which is direct or positive if viewed from one end, 

 and retrograde or negative if from the other ; and this suflices to explain 

 the well-known polarity of electric and magnetic induction. 



Thus far the spiral hypothesis is merely inferential ; but in regard to 

 magnetic wave-motion some strong presumptive evidence may be adduced. 

 It appears from the experiments of Mr. Joule, made more than twenty 

 years ago, that if a suspended mass of copper be, by twisting the suspen- 

 sion, made to rotate between the poles of an unexcited electro- magnet, the 



* The writer has elsewhere applied (Elements of Natural Philosophy, p. 550, note) 

 a definite and intelligible meaning to the construction of those compound terms which 

 must be constantly employed in relation to the conversions of energy. This may be 

 accomphshed by taking the first section of the term to mean the acting cause, the 

 second, the resulting effect : thus a dynamo-electric machine will be one in which 

 dynamic energy is employed to produce an electric current ; and an electro-dynamic 

 engine, one in which a current is employed to evolve dynamic energy. 



