Faraday to Lambert-Adolphe-Jacques Quetelet   23 November 1850

Royal Institution | 23 November

My dear Sir

I ought long ago to have returned you my heartiest thanks for your very great kindness in sending the Portrait¹ I so much desired for my book. It forms a great addition to the pleasure I take in looking into the volume². The only excuse I have is that I have been deeply occupied and I hope that the subject of my thoughts will be acceptable to you. I am vain enough to think that I have found the true physical cause for the periodical & many of the irregular variations of the magnetic needle and perhaps even in part for the magnetic storms. You remember that three years ago I made known the magnetic characters of oxygen in a letter in the Philosophical magazine devoted to the diamagnetic condition of flame & gases³ and spoke generally of its effect in the atmosphere. Since then I have continually thought & worked on the subject & of late have devised experimental means of ascertaining the effects of rarefaction and of temperature separately in relation to the different gases. I find that all the effects of these two modes of change are exerted on the oxygen & none on the nitrogen that if oxygen is rarefied by the air pump it loses in magnetic power in proportion, that if it is heated it loses in proportion, but that in regard to the nitrogen neither rarefaction nor change of temperature produces any effect. Then by a chain of reasoning which is given in the three papers that I have sent in to the Royal Society⁴ supported by facts drawn from other bodies than oxygen & nitrogen I deduce the effect which the daily changes of temperature ought to produce upon the direction of the lines of force of the earth & as far as I have been able to compare the conclusions with the results obtained at Hobarton, Toronto, Washington, Lake Alhabasen Fort Simpson, Greenwich, St. Petersburgh, Cape of Good Hope, St Helena & Singapore the one accords with the other. You will hear more about them soon.

You desire me to send you a copy of the last portrait that was taken of myself and I shall do so on the first occasion that I can find conveyance perhaps by the Royal Society when the papers are printed. Believe it to represent one who has the highest feelings for your character as a Gentleman a Philosopher & a kind friend[.]

Ever My dear Sir | Most Truly Yours | M. Faraday

à monsieur | Monsieur Quetelet | &c &c &c

Address: A Monsieur | Monsieur Quetelet | &c &c &c &c | Observatory | Bruxelles

Postmark: 1850