342 



SCIENCE 



[N. S. Vol. LIV. No. 1398 



transformation, the substances just listed 

 behaved as paramagnetic materials in that 

 I was independent of H and kxl/T. As the 

 temperature falls there is continuity in pass- 

 ing from the paramagnetic state to the fer- 

 romagnetic state. No such continuity, how- 

 ever, seems to exist when one passes from the 

 paramagnetic to the diamagnetic state, which 

 suggests that the causes underlying the two 

 states are quite difEerent. So far this dis- 

 cussion has been largely historical and is 

 given to serve as a background for a further 

 discussion of the theories of Langevin and 

 Weiss which have grown out of the researches 

 of Curie. 



Curie's work seemed to indicate that para- 

 magnetic substances would give infinite sus- 

 ceptibility at absolute zero. This phase of 

 the subject has been very extensively studied. 

 Dewar and Fleming'^ found for solid MnSO^ 

 and liquid oxygen that it did hold down to 

 —186° C. On the other hand the work of K. 

 Onnes and Perrier,^ Oosterhuis'^ and Honda* 

 and Owen^ seemed to show that Curie's 

 second law is not at all true for the majority 

 of paramagnetic substances and that further- 

 more a great many diamagnetic elements 

 disobeyed the first law, viz., that they did 

 not maintain a constant susceptibility as the 

 temperature changed. Tables X. and XI. in 

 the excellent paper of Dushman^" show these 

 discrepancies in a very striking way. These 

 results have led Kunz^^ to remark that, 



It seems to me not justified to maintain Curie's 

 rule, as there are many more exceptions tlian con- 

 firmations. The same is true for diamagnetism. 



5 Dewar and Fleming, Proc. Boy. Soc, 60, 57, 

 1897; 63, 311, 1898. 



6 Onnes and Perrier, Comm. No. 139a, Phy. Lab. 

 Leiden. (See article Oosterhuis, EoninTclyTce Alcad., 

 Amsterdam, 16, 892, 1913-14.) 



' Oosterhuis, Proc. Amsterdam Acad. Sci., 16, 

 432, 1913-14. (Look up bibliography contained in 

 this volume of the Proceedings.) 



8 Honda, Ann. d. Phys., 32, 1910. 



s Owen, Ann. d. FJiys., 37, 657, 1912. 



10 Dushman, Reprint, Gen'l. Elec. Bev., May, 

 Aug., Sept., Oct. and Dec, 1916. 



11 Kunz, Eighth Internat. Cong. App. Chem., 22, 

 187, 1912. 



. . . There are only very few elements which do 

 not vary within the whole temperature range. 

 This weakens the foundation on which Lange- 

 vin and Weiss build their theories for dia-, 

 para- and ferromagnetism. The multitudin- 

 ous works of those already mentioned with a 

 host of others make it all too apparent that 

 the phenomena of magnetism are exceedingly 

 complicated. We must not, to quote Strad- 

 ling,i2 expect too much of any explanation 

 in view of the apparently contradictory facts. 

 The theoretical and experimental investiga- 

 tions of Langevin and Weiss have been very 

 productive of further experimental work and 

 theory so that they must hold a very im- 

 portant place in the future development of 

 magnetic theories. I can do no better than 

 use the method of presentation given in the 

 excellent resumes of the work of these two 

 men which have been made by various English 

 and American writers. 



1. Langevin's Theory of Diamagnetism. — 

 To begin with it is to be recalled that Row- 

 land first demonstrated the fact that a moving 

 charge created a magnetic field; if the charge 

 moved in a circular orbit a magnetic field 

 was produced normal to the plane of the path 

 in which the charge moved. This forms a 

 picture of electronic orbits which we suppose 

 to exist in the flame for the Zeeman effect. 

 If a magnetic field is thrown on to a group 

 of such revolving charges, differences in period 

 of revolution will be produced, in some cases 

 decreasing and in others increasing the period. 

 This gives rise to the double and triple lines 

 which we see in the field of view of the 

 spectroscope. This behavior of electronic 

 orbits lies at the foundation of Langevin's 

 and Weiss's theories. Thus according to 

 Langevin if we introduce a substance into the 

 magnetic field which is diamagnetic accord- 

 ing to the tests we have already described, 

 then the electronic orbits which we suppose 

 surround every atom will be affected in the 

 way we have just described them as being 

 influenced in the Zeeman effect: some will 

 have their periods decreased and others ,in- 



12 Stradling, Journ. Fraiiklin Inst., 180, 173, 

 1915. 



