92 Prof. Faraday on some Points of Magnetic Philosophy. 



course from the extreme of paramagnetic bodies to the extreme 

 of diamagnetic bodies ; and there is no substance within the 

 series which, in association with those on each side of it, may 

 not be made to present in itself the appearances and action which 

 are considered as indicating the opposite polarities of iron and 

 bismuth. How then is their case, in the one or the other con- 

 dition, to be distinguished from the assumed polarity conditions 

 of bismuth or of iron ? — only, I think, by assuming other points 

 which beg the whole question. In the first place, it must be, or 

 is assumed, that no magnetic force exists in the space around a 

 magnet when it is in a vacuum, it being denied that the power 

 either crosses or reaches a locality in that space until some ma- 

 terial substance, as the bismuth or iron, is there. It is assumed 

 that the space is in a state of magnetic darkness (3305.), an 

 assumption so large, considering the knowledge we have of natural 

 powers, and especially of dual forces, that there is none larger in 

 any part of magnetic or electric science, and is the very point 

 which of all others should be held in doubt and pursued by ex- 

 perimental investigation. It is as if one should say, there is no 

 light or form of light in the space between the sun and the earth 

 because that space is invisible to the eye. Newton himself durst 

 not make a like assumption even in the case of gravitation (3305. ), 

 but most carefully guards himself and warns others against it, 

 and Euler* seems to follow him in this matter. Such an assump- 

 tion, however, enables the parties who make it to dismiss the 

 consideration of differential effects when bodies are placed in a 

 vacuum, and to divide the bodies into the well known double 

 series of paramagnetic and diamagnetic substances. But in the 

 second place, even then, those who assume the reverse polarity of 

 diamagnetic bodies, must assume also that the state set up in 

 them by conduction is less favourable to either the exercise or 

 the transmission of the magnetic force than the original unpo- 

 larized state of the bismuth ; an assumption which is, I think, 

 contrary to the natural action and final stable condition into 

 which the physical forces tend to bring all bodies subject to 

 them. That a magnet acting on a piece of iron should so deter- 

 mine and dispose of the forces as to make the magnet and iron 

 mutually accordant in their action, I can conceive ; but that it 

 should throw the bismuth into a state which would make it repel 

 the magnet, whereas if unaffected it should be so far favourable 

 as to be at least indifferent, is what I cannot imagine to myself. 

 In the third place, those who rest their ideas on magnetic fluids, 

 must assume that in all diamagnetic cases, and in them only, the 

 fundamental idea of their mutual action must not only be set 

 aside but inverted, so that the hypothesis would be at war with 

 • Letters, &c. translated. Letter LXVIII., or pp. 260-262. 



