Faraday to William Whewell   10 June 1852

Royal Institution | 10 June 1852

My dear Whewell

I received your pleasant letter¹ which I take as a great compliment; or rather (for I do not care for compliments) as a great encouragement. Now I do not know that I have the ability to enter upon the irregular variations of the Earths magnetism, but I have the wish; and shall some day be encouraged to do so, but not immediately, for the following reasons. The seat of the terrestrial magnetic force is (for us at present) in the earth:- and within the earth there may be causes of variation, not in the distribution of the power only, but also in its amount; the latter varying not simply for the whole mass but probably in different parts at different times. Such variations (within the earth) are I suspect the chief, perhaps the only, cause of magnetic storms, frets &c &c; and as yet we have scarcely any other hold than that of the imagination upon them. On the other hand considering the seat of the force to be in the earth, the force itself extends externally around the planet & its distribution is, as I believe, affected by the medium which is there present, and which, under the influence of the sun, is the chief cause of the daily and of some other regular variations. Now I think I have a hold, by experiment, on this cause of variation; & I further think that if I succeed in making that clear, I shall do far more good to the whole cause & aid more rapidly in the elucidation of the other set of variations, than by going to them at once. For this reason I mean to devote all my thoughts & means to a determination of the rate of variations of the paramagnetic force of oxygen from summer heat or higher, down to 0˚ or if possible 20˚, 30˚ or 40˚ below 0˚. If by such experiments my expectations are confirmed, and we should be able to know surely what is the amount of atmospheric variation; then, subtracting this from the whole amount of effect, how much better we should be able to comprehend the proportion & also the nature of the effect due to internal causes of variation? - and we might then hope that not one or two minds only, but many would start on the search after the cause of the irregular phenomena with far greater advantage, because from a far more assured position than at present. Whatever hopes we have of solving the riddle of terrestrial magnetism must depend upon our successive elimination of the causes of variation; and any one which presents itself in a tangible shape should be pursued as far as possible and estimated in value so that it may be taken from the rest, that they may be studied in a simple form. If we could begin with a magnetic storm the process would be the same as regards the residual phenomena:- but we have as yet little or no hold <<on>> the storms, & I think we have a grasp on the annual & daily variation.

When we really come to magnetic storms I think we shall want needles far lighter than such as are now used for the observations. Needles for such a use ought to be without weight, so as to have neither inertia or momentum[.] How can a bar of some pounds weight tell us the frequency or the extent of rapid vibrations, or give us anything more than a slurring mean? Yet it may be that these variations in their full development are essential to the explication of the mystery. But we shall see by degrees what is wanted & I dare say at last obtain it²[.]

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

Address: Revd. Dr. Whewell | &c &c &c | Kreuznach | Rhine | Prussia