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NATURE 



[June 14, 1883 



whole question of magnetism as existing in the interior of a 

 magnet, and to determine the particular structure for each case, 

 such as neutrality and polarity. 



In a recent paper to the Royal Society, upon the theory of 

 magnetism (Proceedings Royal Society, May 10, 1883), I described 

 the use of and demonstrations obtained by the induction balance. 

 In this paper I propose to confine myself to demonstrations that 

 can be repeated without it, and whose effects can be observed by 

 the aid of ordinary magnetic direction needles. 



That magnetism is of a molecular nature has long been ac- 

 cepted, for it is evident that, no matter how much we divide a 

 magnet, we still have its two poles in each separate portion, 

 consequently we can easily imagine this division carried so far, 

 that we should at last arrive at the molecule itself possessing its 

 two distinctive poles, consequently all theories of magnetism 

 attempt some explanation of the cause of this molecular polarity, 

 and the reason for apparent neutrality in a mass of iron. 



Coulomb and Poisson assume that each molecule is a sphere 

 containing two distinct magnetic fluids, which in the state of 

 neutrality are mixed together, but when polarised are separated 

 from each other at opposite sides ; and, in order to explain why 

 these fluids are kept apart as in a permanent magnet, they had 

 to assume, again, that each molecule contained a peculiar coercive 

 force, whose functions were to prevent any change or mixing of 

 these fluids when separated. 



There is not one experimental evidence to prove the truth of 

 this assumption ; and as regards coercive force, we have direct 

 experimental proof opposing this view, as we know that mole- 

 cular rigidity or hardness, as in tempered steel, and molecular 

 freedom of softness, as in soft iron, fulfil all the conditions of 

 this assumed coercive force. 



Ampere's theory, based upon the analogy of electric currents, 

 supposes elementary currents flowing around each molecule, and 

 that in the neutral state these molecules are arranged haphazard 

 in all directions, but that magnetisation consists in arranging 

 them symmetrically. 



The objections to Ampere's theory are numerous. I. We 

 have no knowledge or experimental proof of any elementary elec- 

 tric currents continually flowing without any expenditure of 

 energy. 2. If we aamit the assumption of electric currents 

 around each molecule, the molecule itself would then be electro- 

 magnetic, and the question still remains, What is polarity? 

 Have the supposed electric currents separated the two assumed 

 magnetic fluids contained in the molecule, as in Poisson's theory ? 

 or are the electric currents them=elves magnetic, independent of 

 the iron molecule ? 



In order to produce the supposed heterogeneous arrangement 

 of neutrali y, Ampere's currents would have either to change 

 their position upon the molecule and have no fixed axis of rotation, 

 or else tire molecule, with its currents and polarities, would 

 rotate, and thus be acting in accordance with the theory of De 

 la Rive. 3. This theory does not explain why (as in the case 

 of soft iron) polarity should disappear whenever the exciting 

 cause is removed, as in the case of transient magneti ation. It 

 would thus require a coercive force in iron to cause exactly one- 

 half of the molecules to instantly reverse their direction in order 

 to pass from apparent external polarity to that of neutrality. 



The influence of mechanical vibrations and stres upon iron in 

 facilitating or discharging its magnetism, as proved byMatteucci, 

 1847, in addition to the discovery by Page, 1837, of a molecular 

 movement taking place in iron during its magnetisation, pro- 

 ducing audible sounds, and the discovery by Dr. Joule, 1842, of 

 the elongation of iron when magnetised, led De la Rive, in his 

 remarkable " Treati-e on Electricity," 1853, to give his theoreti- 

 cal views upon magnetism in the following remarkable words : — 

 "The whole of the magnetic molecular phenomena that we 

 have been studying lead us to believe that the magnetisation of 

 a body is due to a particular arrangement of its molecules, 

 originally endowed with magnetic virtue, but which in the 

 natural state are so arranged that the magnetism of the body 

 that they constitute is not apparent. Magnetism would there- 

 fore consist in disturbing this state of equilibrium, or in giving 

 to the particles an arrangement that makes manifest the property 

 with which they are endowed, and not in developing it in them. 

 The coercitive force should be the resistance of the molecules to 

 change their relative positions." 



Wiedemann, in 1861, gives a theory in which he admits the 

 fluids of Poisson, or the elementary currents of Ampere, as the 

 cause of polarity of the molecule, but believes that the molecules 

 are turned in a general direction in the case of polarity, and that 



in neutrality, like Ampere's, the nagnetic axes of the molecules 

 are turned in all directions. 



Maxwell, in his remarkable treatise on "Electricity and 

 Magnetism," 1881, page 75, gives the following risume of 

 Weber's theory : — 



" Weber's theory differs from Poisson's in assuming that the 

 molecules of the iron are always magnets, even before the appli- 

 cation of the magne.ising force, but that in ordinary iron the 

 magnetic axes of the molecules are turned indifferently in every 

 direction, so that the iron, as a whole, exhibits no magnetic 

 properties." And again, page 429, Maxwell says he agrees with 

 Weber's views, and that neutrality, or unmagnetised iron, has the 

 axes of its molecules placed indifferenily in all directions, and 

 that the act of magnetisation con-ists in turning all the molecules 

 so that their axes are either rendered all parallel to one direction, 

 or at least deflected in that direction. 



I have quoted these several theories which admit of the 

 inherent polarity of the molecule, and in that respect they 

 entirely agree with my own ; but the induction balance at once 

 shows that they are erroneous in the most important part, for 

 my researches have proved that neutrality is perfectly symmetrical, 

 that there is no case of neutrality where the axes of the molecules 

 are turned indifferently in all directions, and that we cannot 

 obtain perfect neutrality except when the molecules foim a 

 complete closed circuit of attraction. 



I believe that a true theory of magnetism should admit of 

 complete demonstration, that it should present no anomalies, 

 and that all the known effects should at once be explained by it. 



From numerous re-earches I have gradually formed a theory 

 of magnetism entirely based upon experimental results, and these 

 have led me to the following conclusions : — 



1. That each molecule of a piece of iron, steel, or other mag- 

 netic metal is a separate and independent magnet, having its 

 two poles and distribution of magnetic polarity exactly the same 

 as its total evident magnetism when noticed upon a steel bar- 

 magnet. 



2. That each molecule, or its polarity, can be rotated in either 

 direction upon its axis by torsion, stress, or by physical forces 

 such as magnetism and electricity. 



3. That the inherent polarity or magnetism of each molecule 

 is a constant quantity like gravity ; that it can neither be aug- 

 mented nor de-troyed. 



4. That when we have external neutrality, or no apparent 

 magnetism, the molecules, or their polarities, arrange themselves 

 so as to satisfy their mutual attraction by the shortest path, and 

 thus form a complete closed circuit of attraction. 



5. That when magnetism becomes evident, the molecules or 

 their polarities have all rotated symmetrically in a given direc- 

 tion, producing a north pole if rotated in that direction as 

 regards the piece of steel, or a south pole if rotated in the 

 opposite direction. Also, that in evident magnetism we have 

 still a symmetrical arrangement, but one whose circles of attrac- 

 tion are not completed except through an external armature 

 joining both poles. 



6. That we have permanent magnetism when the molecular 

 rigidity, as in tempered steel, retains them in a given direction, 

 and transient magnetism whenever the molecules rotate in com- 

 parative freedom, as in soft iron. 



Experimental Evidences. — In the above theory the coercive 

 force of Poisson is replaced by molecular rigidity and freedom ; 

 and as the effects of mechanical vibrations, torsion, and stress 

 upon the apparent destruction and facilitation of magnetism is 

 well known, I will, before demonstrating the more serious parts 

 of the theory, cite a few experiments to prove that molecular 

 rigidity fulfils all the requirements of an assumed coercive force. 



The influence of vibrations, torsion, or stre-s of any kind upon 

 a magnetised steel or iron rod may be seen by striking with a 

 wooden mallet rods of hard and soft steel, also hard and soft 

 iron previou-ly magnetised to a known degree. The tempered 

 steel, owing to its molecular rigidity, will lose but 5 P er cent., 

 the soft steel 60, hard iron 50, and soft Swedish iron 99 per 

 cent, of its magnetism, the amount of loss depending not so 

 much upon whether the metal be steel or iron, as upon its degree 

 of hardness and softness ; and as hard steel requires far more 

 power to magnetise it to the same force than iron, it is possible 

 to imagine a steel so hard that its molecules could not rotate, 

 and that consequently no magnetism could be manifested from a 

 given inducing cause, whilst a perfectly soft iron would give the 

 maximum effect, and instantly return to its previous state. From 

 this we might in error suppose that soft Swedish iron could not 



