102 Prof. Faraday on some Points of Magnetic Philosophy. 



those of the moving wire (36. 55.), or those of voltaic in- 

 duction (6. &c.) ; and their intensity and power is very well 

 shown in the force of Elkington's magneto-electric apparatus 

 and Ruhmkorff's induction coil. Time is concerned in their 

 production, and Professor Henry has shown us, in some degree, 

 that when the currents are moving in helices, the magnetic action 

 across them is for a time cut off or deflected (1730.). These 

 actions are, in every case, simple ; i. e. a line of force in a given 

 polar direction produces, or tends to produce, in a body moving 

 across it, whether paramagnetic, neutral, or diamagnetic (3146. 

 3162.), a current in the like direction ; which current must, as 

 I conceive, be dependent upon a previous like static state. No- 

 thing in the slightest degree analogous to the supposed oppo- 

 sitely polar states of paramagnetic and diamagnetic bodies has 

 ever been discovered amongst them ; — and it has never been said, 

 or supposed, as far as I know, that the two actions, i. e. the 

 magnetic and the magneto-electric, are separate in their essential 

 nature, or that they are not the consistent and accordant, and I 

 must add reciprocal, actions of one force. 



3339. That the copper, &c. are effectual as magnetic media 

 when in the field, may be stated also thus : — 

 Let N, fig. 8, be a magnetic pole, and C a * 1 S« "• 



thick disc or short cylinder of copper. If 



the copper revolve ever so rapidly on its ^\ 



axis, there will be no production of currents ' 



in it; and the magnetic action of N on 

 other magnets will be the same, as if the metal were quiescent 

 or even away. If N recede from C there are then currents in C, 

 though it be not moving ; and though the effect of N upon 

 other magnets, as far as we know them, are unchanged; yet there 

 is then a slight attraction between C and the N pole. If N be 

 made to approach C, the reverse currents and actions occur. As 

 N approaches or recedes more quickly or slowly, the currents 

 produced, and consequent temporary magnetic state, are higher. 

 A cylinder electro-magnet will show these effects very well. 

 The copper has all the time been still, no motion has been pur- 

 posely given to it ; it has been affected by the approximation and 

 recession of the pole, has passed from one state to another, which 

 states remain stationary as long as the poles are quiescent, and 

 it shows every character of a medium affected by the magnetic 

 force. By expedients the currents in the copper may be allowed 

 or prevented ; but whether they be allowed or not, the state the 

 copper medium arrives at is the same. If disallowed as the 

 magnet approaches, but allowed as it recedes, then the current 

 due to the last change occurs, an effect easily shown with a 

 magnet and helix; and this seems to prove very distinctly that 



