418 Dr. Faraday on the Physical Character of 



3278. In this view of a magnet, the medium or space around 

 it is as essential as the magnet itself, being a part of the true 

 and complete magnetic system. There are numerous experi- 

 mental results which show us that the relation of the surrounding- 

 space can be varied by occupying it with different substances ; 

 just as the relation of a ray of light to the space through which 

 it passes can be varied by the presence of different bodies made 

 to occupy that space, or as the lines of electric force are affected 

 by the media through which either induction or conduction takes 

 place. This variation in regard to the magnetic power may be 

 considered as depending upon the aptitude which the surrounding 

 space has to effect the mutual relation of the two external pola- 

 rities, or to carry onwards the physical line of force ; and I have 

 on a former occasion in some degree considered it and its con- 

 sequences, using the phrase magnetic conduction to represent the 

 physical effect (2797.) produced by the presence either of para- 

 magnetic or diamagnetic bodies. 



3279. When, for instance, a piece of cold iron (3129.) or 

 nickel (3240.) is introduced into the magnetic field, previously 

 occupied by air or being even mere space, there is a concentration 

 of lines of force on to it, and more power is transmitted through 

 the space thus occupied than if the paramagnetic body were not 

 there. The lines of force, therefore, converge on to or diverge 

 from it, giving what I have called conduction polarity (2818.) ; 

 and this is the whole effect produced as regards the amount of 

 the power ; for not the slightest addition to, or diminution of, 

 that external to the magnet is made (3218. 3223.). A new dis- 

 position of the force arises ; for some passes now where it did 

 not pass before, being removed from places where it was previ- 

 ously transmitted. Supposing that the magnet was inclosed in 

 a surrounding solid mass of iron, then the effect of its superior 

 conducting power would be to cause a great contraction inwards 

 of the sphere of external action, and of the various sphondyloids, 

 which we may suppose to be identified in different parts of it. 

 A magnetic needle, if it could be introduced into the iron medium, 

 would indicate extreme diminution, if not apparent annihilation, 

 of the external power of this magnet ; but the moving wire would 

 show that it was there present to its full extent (3152. 3162.) in a 

 very concentrated condition, just as it shows it in the very body 

 of a magnet (3116.) ; and the power within the magnet, it being 

 a hard and perfect one, would remain the same. 



3280. The reason why a magnetic needle would fail as a cor- 

 rect indicator of the amount of power present in a given space 

 is, that when perfect, it, because of the necessary condition of 

 hardness, cannot carry on through its mass more lines of force 

 than it can excite (3223.). But because of the coalescence of like 



