Faraday to Antoine-César Becquerel   17 January 1851

Royal Institution | 17 Jany 1851

My dear Mr. Becquerel

I received your letter of the 14th instant¹ yesterday & hasten to reply to it as you desire: first however thanking you for your kind² expressions which will be a strong stimulus to me coming as they do from a Master in Science. I would not have you for a moment think that I put my paper of three years ago³ & that of M. E Becquerels of last year on the same footing, except in this that we each discovered for ourselves at those periods the high magnetic relation of oxygen to the other gases[.] M. E. Becquerel has made excellent measurements which I had not & his paper⁴ is in my opinion a most important contribution to science[.]

I am not quite sure whether you are aware that in my paper of 1847 the comparison of one gas with another is always at the same temperature i.e at common temperatures and it was a very striking fact to me to find that oxygen was magnetic in relation to hydrogen to such an extent as to be equal in attractive force to its force of gravity, for the oxygen was suspended in the hydrogen by magnetic force alone. Phil Mag. xxxi, pp. 415, 416⁵. I do not think that much turns upon the circumstance of calling oxygen magnetic or diamagnetic in 1847 when the object was to shew how far oxygen was apart from the other gases in the magnetic direction these terms being employed in relation to other bodies and with an acknowledgement that the place of zero was not determined[.] If I understand rightly M Edmond Becquerel still calls bismuth & phosphorus magnetic whilst I call them diamagnetic. He considers space as magnetic I consider it as zero. If a body should be found as eminently diamagnetic in my view as iron is magnetic; still I conclude M. Edmond Becquerel would consider it magnetic. He has not yet adopted the view of any zero or natural standard point[.] But this does not prevent us from fully understanding each other and the facts upon which the distinction of oxygen from nitrogen and other gases are founded remain the same and are just as well made known by the one form of expression as the other. It was therefore to me a great delight when I first saw his paper in last November⁶ to have my old results confirmed and so beautifully enlarged in the case of Oxygen & Nitrogen by the researches of M. E Becquerel and beyond all to see the beautiful system of measurements applied to them which is described in his published paper. Pray present my kindest remembrances & wishes to him and believe me to be with the highest respect My dear M. Becquerel

Your faithful Obliged Servant | M. Faraday