William Snow Harris to Faraday   25 April 1851

Plymouth, 25 April 1851

My dear Faraday

I am in possession of your late researches in Electy printed in the First Part of the Philosophical Transactions for this present year¹, with which I am greatly charmed and instructed, and for which I feel deeply indebted to you[.] When I look at what you have done in Science, and your still brilliant progress, I am inclined to say of you, as the Marquis de L’Hospital² said of Newton “Does Faraday eat drink and sleep like other men”?³ Your new discovery of Atmospheric Magnetism has opened a vast field of further research and impressed upon every new fact in this department of Science a peculiar Interest.

Having lately been myself engaged in the further prosecution of inquiries concerning the nature, laws, and mode of action of this species of force, and having arrived at several conclusions, apparently novel and important I have assembled them under the form of a Communication to the Royal Society⁴. My first impulse however was to send the Paper to you, with a view of your looking it over, and presenting it, should you have thought it worthy of that honor - that would have been the course which my great admiration of your Labours and I will add my sincere personal regard toward you, would have led me, to adopt - but I considered, that I ought not to trouble you on such an occasion seeing how much you are hourly occupied in matters of such vast importance to the interests of Science. Thinking however, that the experimental part of my paper, may possibly be interesting to you, seeing that it is involved in those very researches in which you are engaged, and that it embraces new phenomena on Magnetism requisite to be considered, & accounted for, in any further view, we may be led to take of this mysterious power, I have determined on forwarding for your information a rough copy of my paper, with the few following notices, so that you may have no trouble about it, and refer to the facts in it in such way as may suit your convenience. I trust you will not think me intrusive in having ventured on this step - for after all I am not sure whether what I have done may be esteemed of sufficient importance to merit your consideration or not[.]

The First pages consist of Introductory remarks, and a reference to Instruments principally those you saw at the Geological Museum - but with improvements. This is followed by a particular view of the nature and mode of Operation of Magnetic Force, which is considered to arise out of what I have called waves of Induction or Magnetic reverberations set up between the surfaces of the opposed bodies, this may after all come to your theory of Polarized particles - however if you think it worthwhile you may see what is said sec 4 and 5.

The laws of these inductive forces, as given in sec 11, may perhaps be found very well worth consideration - more especially when taken in connection with secns 23, 24 &c in which various laws of reciprocal force are fully elucidated - and all the several results of experiments by Hauksbee⁵, Brook Taylor⁶, Muschenbroek⁷ and others quite reconciled with the primary or more elementary laws of Magnetic force. I think this is so far interesting inasmuch, as it helps to throw light on the nature of Magnetism - more especially in any reference of this peculiar Physical Force, to a general or universal principle as you seem disposed to do[.] So far as I see - we have in the phenomenon of a Magnet attracting Iron or that of two Magnetic poles attracting each other, one end only of a chain in our grasp, the other end of which is out of sight. Taking the reciprocal force near the magnet, it is certainly in no inverse ratio greater than that of the simple distance - as we recede from this into Space - the force becomes as the 3/2 power of the distance inversely - then as the Squares, next as the 5/2 power then as the cubes of the distances inversely as stated by Newton⁸ - and to what other inverse powers of the distances, the force may extend as the action fades away in distance, it is almost impossible to say, without instruments of extreme sensibility such as we can not at present boast of, it is not possible to further investigate this point. You see what I have said about this at Sec. 28. Observe I do not say that you obtain the above laws in every instance successively with the same Magnet so much depends on the stability of the Inductive force. But I have no doubt whatever, not the slightest, of the facts, or that the experiments, can in any way, either Mathematical or Physical, be called in question.

In Sec 14 and following I think you will find a new class of Phenomena, unless I am unacquainted with all you & others have effected - e.g. you will find a curious and interesting example of a diminished Magnetic Intensity by an increase of surface, being in magnetism, precisely the same experiment and class of fact, which Franklins⁹ Expet. of the Can and Chain is in Electricity¹⁰, or of any analogous experiment in which by extending the Surface the Electrometer falls see Fig 7 Sec <¹¹>. You will further see <¹²> that a hollow tempered steel Cylinder becomes equally if not more powerfully magnetic than a similar solid-tempered steel Cylinder of the same diameter - shewing that it is the Surface and not the Mass which is concerned. That a soft Iron Cylinder made to fit, and passed into a tempered hollow magnetic Cylinder operates as a sort of discharging rod, and permanently discharges as it were the opposite polarities, leaving a residuum as in the Leyden Jar &c &c. There are a class of facts here which perhaps may be interesting to you[.] We have not I think as yet done enough in the way of investigating internal magnetism, as in your Electrical cage, you suspended and lived in¹³.

Sec. 34 - which treats of magnetic quantity, and its law of measurement is necessarily in association with some of your views sec. 2870¹⁴. I have not the slightest doubt but the law and condition of charge, is identical with Electricity the force of attraction is as the square of the quantity. Sec 35 contains my apology for terms, and refers to an Experiment Fig 8. with which I have been much satisfied & pleased from the great, I may say the extreme precision of its results. I do not think that such a combined action for the measurement of Volta magnetic force has been as yet effected. It served me in magnetism as the Unit Jar did in Electricity - and we have now I think a means at command for determining how much more magnetism we have in the pole of any one magnet, or in any other point, than in the pole &c of any other magnet. The Expt in detail is given <(36)> the Law for quantity is in <(34)> afterward proved to be true.

In sec. <(42)> is the problem of the magnetic development in different points of a Magnetic Bar, which has not always been accurately and definitely stated[.] Finally I have thought it worth while to refer in the end of this Paper to the peculiar para<squig>llism in the phenomena of the Electrical Jar and the Magnetic Bar, and to what Newton and others of the more remote periods of the R.S have advanced on this subject, and which instead of being open to the severe animadversions and unmerited criticisms of many eminent mathematicians¹⁵, are I firmly believe perfectly true in all their details and results, and quite consistent with demonstrable laws of magnetic force - you will see my views on this subject <(45)>[.]

I do not see how it is possible to consider Magnetism as a central force or emanation from a magnet spreading out into space and getting weaker in Proportion to the amount of space spread over:- all our experience is to my humble apprehension against such a deduction - the action must be after all referred to an action between terminating planes; much after the fashion you have described in 1299, 1302, 1301 1163¹⁶ &c - and in various other parts of your researches. Two terminating planes or surfaces with something going on or established between them is the immediate feature to me of both Electrical and magnetic force thus

In the attraction of a magnetic Pole n and a similar mass of Iron m, end on, as it were, as in the above Diagram I do not at all believe, that the forces uniting in the other parts & about the center of the Bar m enter into the surface action at the pole -

and for the reasons I have given <¹⁷> <¹⁸> <(44)> &c. It is not therefore as stated by Robison¹⁹ a sort of balance of Electrical attractions & repulsions we have to consider, as referred to all points of the mass of the opposed bodies in such a case²⁰; but an exclusive action between the surfaces. The something which goes on between the surfaces you call polarization of particles. So far as I see the general principle is true, but I think we shall have to refer this polarization to some medium different from that of air for I have no doubt whatever but that the force between a plane magnetic pole and an Iron Plate which goes on in vacuo in no sense differs in its nature from the force between a plane polar electrified surface and a neutral conducting plate. I am quite sure that both these actions are identical all that the air does in Electy of high Intensity may be to arrest the passage of the Electy, thus in magnetism is not wanted. Robison seems to think (Mech. Phil. vol iv p273) that the law of attraction as observed between magnets or between magnets & Iron, must be different from the real law of magnetic action - because he says the magnetism is always increasing or decreasing with the distance²¹ - but the ground I take in my paper is, that it is really this increasing or decreasing magnetism as depending on induction which constitutes magnetic action - it is in fact the combined effect of induction between the opposite poles at different distances which gives the law of the force; this is the real magnetic action, there is no other. It appears to me that there has been a great bias with many profound mathematicians in favor of a certain law of magnetic force, which they think must be the same as the law of Gravity, and if we do not find it so by Expt. the Experiments are false, we ought to find it so. The more modern & French Theorys of Electricity & Magnetism depend much on the truth of this position all their fine mathematical superstructures are built on it - and I really do think in many instances, that if it were a point at issue between Poissons Mathematics²² and the course of Nature, very many would give it in favor of Poisson[.] It is quite curious to see how severely every Experimental result is handled which does not coincide with the law of the inverse duplicate ratio of the distance. Robison cuts down at one sweep all the valuable expts of Hauksbee²³, Brook Taylor²⁴ Whiston²⁵, Muschenbroek²⁶ & others²⁷, says in as many words they are worthless - that Electrical attractions & repulsions are not the most proper phenomena for declaring the precise law of variation - yet was it from those same attractions and repulsions that both Coulomb ²⁸ and Lambert ²⁹ deduced their law of magnetic force - Lambert especially resorted to the method of Hauksbee & Brook Taylor, certainly in a more refined way - now their experimental inquiries are quoted with confidence; and in no way objected to, in fact they were considered to have arrived at the true law of the Force: then again Newton having observed that the Magnetic attraction decreases in a certain case in the Inverse triplicate ratio of the distance - we are told in as many words by Biot, that Newton was ignorant of the whole matter³⁰, and had not accurate Ideas of magnetic Phenomena, and so in a variety of other instances. In fact without in any way entering as you have done into a severe and close investigation of nature by Experiment many profound Mathematical men have been content to adopt a certain set of principles, derived it seems to me, not always from very unexceptionable experiments - and they seem determined to bend every thing to those principles. For my self I have no belief in Electrical & Magnetic fluids in their hypothetical density & distribution, in virtue of the assumed law of their constitution &c. There is something to come yet far beyond all this - however we are still in the dark about it. I have read over your attempt to establish a relation between Gravity & Electricity³¹. I have not myself much hope of success by any direct experiment. The results of the two forces being so very different - I can conceive no identity in these forces except through a sort of Aethereal medium in which all matter may be conceived to float and different relations or affections of which to the particles of common matter is in one case Gravity in another Electricity: but it is in vain for me to speculate on such things at this moment. You are the only Philosopher on Earth likely to throw light on the question[.]

I had always great misgivings relative to the changes which might ensue in vibrating a magnetic needle in air, and I pointed out some of these changes in my papers in the Edinb. Phil. Transactions for 1834 vol xiii, “On the Investigations of Magnetic Intensity &c-”³² and I felt quite assured at that time, that Christies Expts. relative to the Influence of Light Phil. Trans. 1825³³ were disturbed by taking the oscillations in air - all of which I have enlarged on at the close of that Paper sec 33. And I think you may find some Experiments there immediately coinciding with and bearing on what you say 2871³⁴ and the direct connection of the two is really very striking see also sec 34 and 35 of my paper above quoted. Your observations on Atmospheric Magnetism confirm my view of the propriety of observing Intensity oscillations in vacuo - which I have always done as in the long series of Expts in the Phil. Trans for 1831 p69³⁵.

I take it for granted, that by this time I have tired you out, but I find the subject so very interesting that I could continue to write about it to almost any extent, especially to you. I will however now bid you adieu & will subscribe myself your very faithful & affect[ionate] friend

W. Snow Harris