104 Prof. Faraday on some Points of Magnetic Philosophy. 



of the ends which were to be brought together, or by withdrawing 

 the electro-magnets a little the one from the others, and then a 

 ray of light could be passed into or across it ; magnetic needles 

 or crystals of bismuth could be suspended in it; — a ring helix 

 could be introduced and rotated there ; and the motions of any- 

 thing within could be observed by the eye outside. 



3342. A small magnetic needle hung in the middle of this 

 space, gave no indication of any magnetic power; near the open 

 edges and angles vibrations occurred, but they were as nothing 

 compared to the powerful indications given outside the chamber; 

 even when the needle was many inches away. A crystal of bismuth 

 was entirely indifferent. A piece of soft iron hung on a jointed 

 copper wire within the chamber showed no trace of magnetic 

 power, whether examined by the little needle or in any other 

 manner. Iron filings on a card across the chamber were not 

 affected in the middle part, but only near the partly open angles. 

 A ring helix of many convolutions, having its terminations pass- 

 ing out at opposite corners, was connected with a very sensitive 

 galvanometer and rotated ; it showed no trace of inductive action. 

 Numerous other experiments were made, but with results alto- 

 gether negative. Attempts (though desperate) were made to 

 ascertain if any electro-chemical conditions were induced there, 

 but in vain. Every kind of trial that I could think of, not 

 merely by tests of a polar character, but of all sorts, were insti- 

 tuted, but with the same negative result. 



3343. It was of course not to be expected that any polar, i. e. 

 any dually related polar, action could be exerted in this place ; 

 but if the polarities can exist without mutual relation, we might 

 surely expect some condition, some tonic or static state, in a 

 chamber thus prepared and surrounded with a high intensity of 

 magnetic power, acting in great concentration on one particular 

 spot or substance. But it is not so ; and the chamber offers a 

 space destitute of magnetic action, and free, under the circum- 

 stances, from magnetic influence. It is the complete analogue 

 of the space presented within a deep metallic vessel or globe*, 

 when charged with electricity (1174.). There is then no elec- 

 tricity within, because that necessary connexion and dependence 

 of the electric duals, which is essential to their nature, cannot 

 be. In like manner, there is no appearance of magnetic force 

 in the cubical chamber, because the duals are not both there at 

 once, and one cannot be present without the other. 



3344. There are many ways of examining in a more or less 

 perfect manner these neutral and highly instructive magnetic 

 places. A cavity in the end of an electro-magnetic core or a 

 permanent magnet will present similar phenomena, and in some 

 respects even more perfectly ; for though a trace of power will 



* Phil. Mag., Oct. 1846, vol. xxix. p. 25/, note. 





