William Snow Harris to Faraday   28 April 1839

Plymouth April 28, 1839

My dear Faraday

I am about to trouble you with a somewhat lengthy communication. I hope your patience will out live the perusal of it - Having at length completed a closing Paper on the Elementary Laws of Electricity¹ - commenced, and in great part worked out, before your last Paper was read² - I have sent it forward by this Post to Mr Christie. Your admirable researches on Induction & Attrac‑tion, have not of course escaped me. I have looked them over with exceeding pleasure and Interest. This Paper on the same subject would have been forthcoming before, but that the suffering Illness and death of my Mother³, as also of My Aunt her Sister, not long since, together with numerous matters of business always the plague of those engaged in Physical researches in the Country absolutely prevented it. You well know, we cannot invent and make apparatus, & work out results in a loose hurried way - at least if they are to go for any thing hereafter but to proceed. The Results of my recent Inquiries do not so far as I can see at all oppose themselves to your view of Electrical In‑duction. I think it highly probable that the action is between contiguous parti‑cles in a dielectric as you state modified by the kind of matter through which it is exerted⁴[.] I hope soon to have a word with you on this interesting subject and if you should think I can manage to work up a few of the Experiments & results so as to be of Interest for an evening meeting of the R. Institution - I shall be happy to do so⁵[.] I hope to be in London about the 15th of May. The following are some of the principle [sic] facts contained in my Paper.

1°. Evidence in favor of the conclusion that Electricity is an unknown species of matter, differing essentially from common matter[.]

2°. That it is in some way associated with the particles of ordinary matter, as to admit of being changed in respect of quantity either in different bodies, or in different parts of the same body.

3°. That Induction so far as relating to a given substance is a change of quantity in different parts of it[.]

4°. That the action by which this change is effected, is equal in all directions[.] Thus whether it take place in a straight line thus <-><->n or thus <-><->|n the action upon n is the same - for the same circumstances.

5. The Quantities of Electricity which a neutral Body free ceases to hold in Equilibrio as the distance from the charged body is increased, are inversely Proportional to these distances.

6. The Induction upon an insulated body indefinitely thin, is a vanishing quantity.

7. The Quantities of Electricity which an insulated body (in which the opposite Electricity is constant) ceases to hold in Equilibrio as the distance from the charged body is increased, is as the <root> of these distances.

8. The attractive force between two bodies is not in the inverse ratio of the squares of the distances except one of them be free and the other have an indefinite quantity of charge, in respect of the two opposed surfaces[.]

9. In all cases of force between a positive & negative surface permanently charged at first, (not by Induction) and which are of small thickness the force is as the distance inversely[.]

10. The Force is as the distance inversely between a charged & insulated neutral body[.]

11. An Induction similar to that in Conductors can take place in Glass or other dielectrics - when it does it is a sort of forced disturbance of the particles in place. In the conductors there is change as to Quantity in a given point beside. (I believe when the particles begin to move out of their place in glass or other dielectrics in consequence of violent tension the bodies rupture or break up in some way.)

12. The attractive force upon a thin neutral disc, insulated, may in respect of the force upon the same disc free, become indefinitely great. In the case I tried it was as 400:1.

13. The attractive as compared with the Inductive power between two bodies one charged the other free, are exactly alike.

14. The Quantities of Electricity displaced in an opposed neutral free body by a positively charged body are inversely as the square roots of the distances between the opposed surfaces and as the Quantity accumulated directly[.]

15. In the attraction between two bodies the quantities existing at different dis‑tances on the opposed surfaces, are as the square roots of the distances inversely[.]

16. All the conditions of two attracting bodies are reducible to those of the Leyden Experiment[.]

17. The Attractive force may be calculated between a charged & neutral body of any form whatever, whether planes, Spheres, Cones or Paraboloids &c on the supposition that the forces are parallell [sic] - that they are as the number of Points directly and as the squares of the distances between the Particles inversely.

18. If the neutral body be insulated we may calculate the forces by the preceding laws.

19. In every case of attraction between a charged and neutral body - some portion of the charge is continually accumulating on the charged near surface - In the case I have given of a cylinder A charged with a given quantity, and acting on B neutral and free - about 1/5th of the whole quantity was on a alone when B was not present. When B was placed at .2 of an inch distance about .4 more appeared there - at .4 distance only .2 more appeared there in addition - and so on as the distances inversely - but the whole quantity at a (viz) that originally there + that added by induction was always as the square root of distance a x exactly.

20. The force of attraction is always as the Induced force directly & as the distance inversely. (The Induced force being constant). Untill your researches appeared I could never well understand what there [sic] distance had to do with the matter - having been long since convinced, that attraction in Electricity is not to be associated with forces supposed to emanate from a center. I speak of the common attraction between two bodies - you have shewn that it depends upon the domination of the particles of the Dielectric through which the Induction takes place.

With respect to the Elaborate Theorys of Electrical Action, Advocated and maintained upon the justly accquired [sic] reputation of the French Mathe‑maticians I am disposed to view them with great distrust. At least I know that many of the most vital of the physical data upon which they rest, are false, and I believe others begin to think the same now[.] Although, when I first stated that Electricity was not confined to bodies by Atmospheric Pressure many of our Mathematicians of excellent Theoretical Learning considered my views as unreal. In the mean time however, not one of them ever tried an Experiment. I remember at one of the Early meetings of the British association, getting something like a civil dressing for what was con‑sidered an inconclusive Experiment; at variance with the highest Mathematics of Electricity⁶[.]

Your researches are the only instances in which the whole subject of Electricity has been fairly grappled with. Every one engaged in this interesting Department of Science, must without any undue praise allow, that you have done more to advance & enrich it than has been effected by the accumulated researches of all your predecessors[.] I speak as to the question of its general nature & properties especially[.]

The operation of Repulsion has been always a sort of confusion in my mind. It appears to me (anomalous as the expression may be) to be after all, another form of attraction. I mean by Repulsion the separation of two bodies similarly Electrified and free to move. The Inductions go on, or attempt to go on upon each body just as if one was charged, & the other neutral - and there is evidently a disposition of the Electricity with which each is charged to change place, just in the same way as the particles would do in a neutral body - only in the accumulated plate, there are more particles, and greater tension. If we call this repulsion - then I don't see why common Induction is not repulsion - and the first tendency of a charged body is to repel, not attract a neutral body. All the Mechanical Theory of Repulsion by Biot, Hauy⁷ & others is evidently a fallacy⁸. It serves however as a Peg to hang out a few equations to dry upon. Any thing for a differential.

In the attraction also between two bodies, suppose the Planes they say since every particle of Electricity on A = m attracts every particle on B = n therefore force of one particle m to n will be as n and force of all the particles on m to n will be m x n &c[.] But it must be at least allowed that since the force of one particle say at B is not the same for all the particles on A - that is to say Force on c is less than force on q &c therefore the attractions are constantly differing & unequal - hence it can not be as m x n it may be as some function of it - but it surely can not be as mn[.] But after all the oblique forces Ba Bc &c may (since force is as 1/D⁹) become at last so small in respect of the exactly opposite and nearest neutralizing Particles q q' that they may be neglected and at last the force be reduced to a system of plle forces thus The fact is we know little about the matter, and I suppose we never shall until you, or somebody of equal Philosophical Power, like you shall tell us. There is another thing here to be considered. If we suppose two particles + and - to be attracting each other thus + -

o o

and we place a minus particle at a thus

+ -

o o

-a

then the force between the first two particles becomes extremely diminished and may be made to vanish altogether by placing a positive particle at b thus

+ -

o o

-a +b

that is to say the actions at -a and at +b upon the original particles will be exclusive - but something of this kind happens in oppositely attracting bodies say two spheres[.] Not only is particle b greatly neutralized by near particle a and its force on a particle c diminished by the increased oblique distance bc in addition to this - but the distant particle c is also greatly neutralized by an opposite particle c' - the same may be said of d and d' in respect of particles a and b hence the forces may at last become parallell [sic] forces thus which I really believe is the case, and the commencement of the Proposition would be. Every particle on A attracts a corresponding and opposite Particle on B - hence in Planes if f = force of one Particle and a the number of Particles then Whole Force is as f x a or as fa &c

But in spheres this expression will vary - as I have shewn in my first papers¹⁰[.]

Before concluding this long letter - I recall to my mind a kind note which you was [sic] so good as to send me in reply to my communication, requesting your opinion upon Lightning Conductors¹¹. I was hurried out of London at the Time, owing to the illness of my mother. I had not time to say any more about it then - and a good deal of domestic trouble has since prevented me. The fact is I ought not to have asked you for any opinion on this subject - but I was at the time a good deal bewildered - and I acted under the suggestion of a friend, who was interested in endeavoring to get the Conductors fairly dealt with by the Government - and who was very intimately acquainted with the Chancellor of the Exchequer¹². Pray excuse my having done so[.] Who is there as observed by the celebrated Roman Poet "Wise at all hours"¹³. With respect to my system of defending shipping from Lightning. It is impossible that I should not feel deeply interested in it: not more from personal considerations, than on grounds of general science. One of my principle objects has been to get a History of the cases of Damage by Lightning not only in our Navy, but in the Merchant Service, having evidence that ships frequently perish from this source of danger. The amount in the Navy of damage done, loss of Life &c. is quite frightful - as you may perceive by the accompanying paper¹⁴. I looked to obtain many important facts connected with Atmospheric Electricity - some I have arrived at, as may be seen by my late Papers in the Nautical Magazine, copies of which I hope soon to send you¹⁵. We have had no less than 7 ships of the Navy damaged by Lightning within the last 12 months. In one case the Rodney of 92 Guns - the ship was set on Fire - Two men killed, and the M Mast rendered useless - added to which the ship was detained at Malta, under an expensive refit in consequence, at a cost of 100úa day & upward to the Country¹⁶. I do not conceive the Naval Department is justi‑fied in throwing Science overboard & allowing all this to continue when evi‑dence exists, that it can be prevented. I have a word or two to say to you respecting your late Papers in the Transactions when we meet[.]

Ever my Dear Sir | Faithfully & truly your sincere friend | W. Snow Harris

P.S. I have sent my Paper to Mr Christie at the RS¹⁷[.] If you feel any interest about it - I dare say he will let you have it for perusal - previously to its being read[.]

Michael Faraday Esq | DCL, FRS &c &c