March 13, 1884] 



NA TURE 



459 



Japan, and, I may add, the West Indies, it would appear 

 that the crust of the globe is practically in a constant 

 state of tremor. The variations in these movements are 

 more law-abiding than the large earth movements, and 

 they show a direct relationship to barometric fluctuation. 



Their relationship to manyothertelluricand atmospheric 

 phenomena, together with their cause, has yet to be dis- 

 covered. As every one has the opportunity to observe 

 these phenomena, they call for attention. Just as a tur- 

 bulent sea outraces a coming typhoon and gives mariners 

 warning of approaching danger, it is possible that these 

 microscopic disturbances of the soil may hold connection 

 with subsequent phenomena, and lead us by their study 

 to the better understanding of the complexity of phe- 

 nomena with which we are surrounded. 



Tokio, Japan JOHX Milxe 



THE MECHANICAL THEOR Y OF MAGNETISM 



T F Prof. Hughes were as great a master of writing 

 ■•• English as he is of experimenting, his views on 

 magnetism would receive speedier acceptation, for they 

 would then probably be understood without that close 

 study which his involved sentences and heterogeneous 

 paragraphs now demand. It is very remarkable that 

 such an ardent worker, such a deep thinker, and such a 

 clear and simple experimenter should have such difficulty in 

 expounding his views on paper. His experimental demon- 

 strations are always clear and convincing, his recent lecture 

 at the Royal Institution appealed to every degree of intel- 

 ligence present, but his papers at the Royal Society want 

 some strong external directing influence to render their 

 meaning evident. 



What is magnetism, according to this expert philo- 

 sopher? It is an inherent quality of the molecules of 

 matter, as determined and constant as that of their gravity, 

 affinity, or cohesion, and like these qualities it diifers in 

 degree with every kind of matter. He does not attempt 

 at present to define it closer than this. We cannot tell 

 what gravity is, neither need we say what magnetism is. 

 All Prof Hughes says is that every molecule in nature is a 

 little magnet imbued with a certain polarity varying in 

 degree but constant for each substance, in virtue of which 

 it has a north and a south pole along the same axis, and 

 that the only change that takes place is a change in the 

 direction of this polar axis. When these molecules are 

 symmetrically arranged by some external directing influ- 

 ence, so that all their poles lie in the same direction, we 

 have evident magnetism. Iron becomes a magnet in 

 virtue of the fact that its molecules are free to move under 

 the influence of external magnetic action, while copper is 

 not a magnet because its molecules are immovable and 

 irresponsive to the same cause. Steel becomes per- 

 manently magnetised because its molecules are rigid, and 

 retain the axial direction impressed upon them. Soft 

 iron is readily demagnetised because its molecules have 

 great freedom of motion. Coercive force is therefore 

 simply absence of freedom of molecular motion — it is, 

 indeed, molecular rigidity. The extent to which the axis 

 of polarity can be deflected from its normal direction is 

 its point of saturation. 



Evident magnetism is the symmetrical arrangement of 

 the polarised molecules along one line ; neutrality is 

 symmetrical arrangement of the same molecules in closed 

 curves. In both cases the sum of the magnetic influence 

 of all the molecules is the same ; but in evident magnetism 

 it is directed outwards, in neutrality it i; directed inwards. 

 Remaining magnetism is partial neutrality. The experi- 

 mental way in which Prof. Hughes demonstrated these con- 

 clusions is the most beautiful investigation he has yet made. 

 He proves the existence of the same polarity in the atmo- 

 sphere and in the ether, and he attributes diamagnetic 

 efifects to the higher magnetic capacity of the ether than of 

 the substances suspended in it. It is therefore a difteren- 



tial action. Molecules, moreover, have inertia — they resist 

 being put in motion ; and when in motion they resist 

 stoppage — they possess momentum. The direction of 

 the axis of polarity can be displaced by the physical 

 fcrces, such as mechanical stress, heat, or electricity. He 

 shows that mechanical motion, heat, and electricity are 

 of similar kind — they are vibratory, or some mode of 

 motion. Magnetism, however, he considers not to be a 

 mode of motion, and therefore it is not a physical force. 

 It is simply an arrangement of the molecules of matter 

 in symmetry or dissymmetry under the influence of some 

 physical force. He seems to imply, though he does not 

 directly say so, that the influence of electric currents upon 

 magnets is not due to any direct action between them, 

 but to the fact that the currents have polarised the ether 

 in which both are suspended. 



His views are very broad and highly suggestive, but 

 there are some points that are not clear and that demand 

 further elucidation. Why, for instance, does mechanical 

 elongation and contraction take place when bars of iron 

 are magnetised and demagnetised ? How can heat and 

 strong sonorous vibrations be produced unless there be a 

 considerable expenditure of energy.' How does he 

 account for the attractive and repulsive properties of 

 magnets, and for magnetic induction ? He has certainly 

 wrested magnetism from the realms of hypothesis and 

 brought it within the domain of theory. The days of 

 Coulomb and Poisson's fluids and Ampere's elementary 

 currents of electricity are over ; the molecular character 

 of magnetism is experimentally established ; but what is 

 a molecule, and how becomes it polarised unless it be in 

 rotation ? How does the external directing influence act .' 

 We are also inclined to ask. Has Prof. Hughes sufficiently 

 grasped Ampere's theory? It was purely mathematical, 

 based on the assumption of the circulation of currents 

 around each molecule. He goes no further than Ampere 

 did, for he has not answered the question. What is 

 polarity? In fact his polarised molecules are all little 

 magnets, and no theory of magnetism will be complete 

 until it explains these little magnets. Thus the difference 

 between .Ampire and Hughes is the difference between a 

 current and a magnet. 



However, on the assumption that a molecule is a 

 magnet, Prof. Hughes has built up a very complete theory, 

 which he has demonstrated experimentally in a way that 

 places him in the very front rank of experimental philo- 

 sophers. 



NOTES 



The number of candidates up this session for the Fellowship 

 of the Royal Society is sixty-seven. 



We understand that Sir Joseph Hooker has been nominated 

 one of the vice-presidents for the Montreal meeting of the British 

 Association. Instead of Mr. Crookes, Prof. W. G. Adams 

 will give one of the public lectures. For the reduction of 

 the fares of members the sum of 14,000 dollars has been 

 allotted, only tho e elected at or before the Southampton meet- 

 ing being entitled to share in the subsidy. This is in addition 

 to the liberal reductions that will be made by the .'Steamship 

 and railway companies. All the American railways will reduce 

 their fares by one-half. The American Association, which meets 

 at Philadelphia on September 3, has given a cordial invitation to 

 the Montreal visitors to take part in its meetings and excursions. 

 Those wishing to share in the subsidy of 14,000 dollars mu^t 

 apply before September 25. For the Aberdeen meeting in 1S85, 

 Sir Lyon Playfair will be proposed as president. A well-attended 

 meeting of the Organising Committee of the Chemical Secticn 

 has been held under the presidency of Prof. Roscoe. Promises 

 of papers were received from several well-known chemists, and 

 a small executive committee was formed to draw up a list 

 of papers and to communicate with Canadian and American 



