Faraday to William Whewell   22 August 1850

Upper Norwood | 22 Aug 1850

My dear Sir

I am living and working at Norwood, and so lost the great pleasure of seeing you & what would have been more of hearing you[.] One can consider many things in talking which writing is very unfit for. I received with thankfulness your kind letter¹ and have since, then in my notes & M.S., used the word Paramagnetic ² which will serve my purpose well if after a little further explanation you think it is is [sic] (as I imagine) right. I conclude that a long piece of soft iron unable to retain magnetism would in a field of equal magnetic force stand in the direction of the lines of force, still the power which can make it do so must be exceedingly small in effect, for I imagine it would require an extremely delicate apparatus to shew the pointing of a bar of such iron under the Earths force which we may take as presenting a field of equal force. The diamagnetic power of bismuth or phosphorous is exceedingly small as compared to the corresponding magnetic power of iron & there is no chance that a bar of either would stand transverse to the Earths lines of force. I have found lately that such a bar does stand transverse in a field of equal force made by two walls of iron 5 inches by 3 inches 3/4 of an inch apart. But then a piece of Iron³ destroys such a field as one of equal force for it generates contingent poles in the parts of the iron walls opposed to its ends & the phosphorous as I believe produces a reverse effect equivalent to a destruction of the power there. Hence both the case of the Iron & the phosphorous fall as respects by far the greater part of their effect & perhaps the whole as to position into the law I gave originally - that Magnetic (paramagnetic) bodies pass or tend to pass from weaker to stronger places of magnetic action and diamagnetic bodies from stronger to weaker.

I have been driven to assume for a time especially in relation to the gases a sort of conducting power for magnetism[.] Mere space is Zero. One substance being made to occupy a given portion of space will cause more lines of force to pass through that space than before and another substance will cause less to pass. The former I now call Paramagnetic & the latter are the diamagnetic. The former need not of necessity assume a polarity of particles such as iron has when magnetic and the latter do not assume any such polarity either direct or reverse. I do not say More to you just now because my own thoughts are only in the act of formation but this I may say that the atmosphere has an extraordinary magnetic constitution & I hope & expect to find in it the cause of the annual & diurnal variations, but keep this to yourself until I have time to see what harvest will spring from my growing ideas.

I am My dear Sir | Most Truly Yours | M. Faraday

Rev. Dr. Whewell | &c &c &c