Faraday to George Biddell Airy   10 June 1852

Royal Institution | 10 June 1852

My dear Sir

Your letter¹ stirs up a great many thoughts in my mind which I have been obliged to leave at rest for a time, simply because experimental work is slow work, & strength & health are limited. My next occupation must be the determination, if possible, of the amount of change in the paramagnetic force of oxygen (or air) by depression of temperature to 0˚, and if possible to -40˚. or -50˚; and at different degrees of pressure or condensation. These data are essentially necessary for the development of the effects which occur under the head of atmospheric magnetism; and which as I believe include a large part if not the whole of the daily variation & much of the annual variation. In the mean time it is a great thing that other persons should be moved to collate and analyse the results of observation; & separate as much as possible the compound result which appears in the continuous stream of a continued set of perfect observations, into such subordinate parts as the periodical variations and the irregular or anomalous phenomena:- for until the great result is in some measure analysed & referred to the various parts that make it, there can be but little hopes of clearing up the scheme of these most complicated phenomena. Therefore I think that such analyses as Sabines² of the larger variations will be very useful in due time.- M. Lamont has already been moved to search, & has, he says, found a recurring cycles of ten years³[.]

To me, the phenomena of fret, storms &c have far greater attraction than the periodical variations already referred to: but we have now some hold of the latter and little or none of the former. They, i.e the former appear to me as probably due chiefly to actions within the magnet i.e the earth; and may have little or no relation to the action of the surrounding medium. If it be so, to determine the condition of a magnet (as the earth) producing variations of such large extent, with such rapidity, and so general in their influence, is a problem of such difficulty that we can only hope for its solution by degrees and knowing so little of the interior of the earth as we do, at first seems almost hopeless. Nevertheless to know, as I now do, that a perfectly invariable magnet, as regards the amount of force⁴, may have the external disposition of its power varied to a very large extent, either suddenly or slowly, without the least change in the sum of power externally, is one point of rest and one ground of hope for the mind. Another is the power which, I hope, the mathematician has of pointing out what sources of change or irregularity are external to the magnet (or earth) and what internal. I think I have heard that Gauss has done something of this kind⁵. If we could separate the variations due to external causes from those caused by internal action, it would certainly clear up the subject in some degree. Hence it is that I must, (being already in the path,) work out the effect of temperature on air as far as I can, before I attempt to meddle with the causes of action within the earth; and, indeed, if I succeed in this first object there are then others waiting for me, which seem to present better handles for experiment than the internal state of the earth[.]

But I hope in a week or two to have another paper for you⁶, and then if you like I will come some day to the Observatory. It would be a great treat to me, and a source of great instruction, to have a talk with you over some of the records of irregularity, storms &c and over the instruments[.]

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

G.B. Airy Esq | &c &c &c