278 



SCIENCE 



[N. S, Vol. XLVI. No. 1186 



7. In 1907 and again in 1908 "Weiss' 

 reached the conclusion, through a series of 

 magnetic determinations at various temper- 

 atures, tliat the atomic magnetic field of 

 ferro-magnetie substances is of the order 

 10' gauss. 



8. At about the same time, that is, in 

 1908, Ritz^ gave an elaborate discussion of 

 a molecular model designed to account for 

 the occurrence of series among spectral 

 lines. He recognized the force of Lord 

 Rayleigh's objection to the assumption of 

 a model in which the electrons vibrated 

 under either mechanical (elastic) or elec- 

 trical forces, since such forces give equa- 

 tions involving squares of the frequencies. 

 He therefore assumed the electrons to vi- 

 brate or describe orbits in planes at right 

 angles to the lines of magnetic fields, under 

 which conditions the reciprocal of the 

 wave-length, 1/A, is given by the equation 



1 ^eff 

 X mv 



in which e is the electronic charge, m the 

 electronic mass, H the magnetic field, and 

 V the velocity of light. Hence for this 

 equation to apply to the spectral region of 

 the average Balmer series H must be of the 

 order of 10' gauss. 



At the distance r from the adjacent pole 

 of a magnet whose pole strength is /j., and 

 length I, 



and 



"^"{v^-vhy} 



1 ^ Me r 1 1 ] 



X mvXr^ {r + iyj 



If Z = ns and r = as 



X s'^mv 

 If a = 2 



\a^ {a+ nY J ' 



n = 1, 2, 3. 



■il l—\ 



\T- {2+ ny j 



ijour. de Phys., 6, p. 661, 1907; 7, p. 249, 1908. 

 B Ann. der Fhys., 25, 660, 1908. 



which is identical with Balmer 's equation 

 for the hydrogen series. 



Hence an electron vibrating at the dis- 

 tance 2s from such an elementary magnet 

 of length s and proper strength will give 

 the spectrum line H ^ . If 2, 3, etc., of these 

 elementary magnets should be placed end 

 on, the electron would emit H , H , etc., 

 respectively. 



Ritz does not state what he considers the 

 probable origin of the elementary mag- 

 netic field. As above explained, however, 

 it conceivably may be due to the orbital 

 revolution of the electrons themselves. 

 Further, the different magnetic fields de- 

 manded by a Balmer series may, perhaps, 

 be provided by a number of concentric 

 rings of electrons, the field abruptly chang- 

 ing on crossing each ring from one to 

 another interspace. This conception ob- 

 viates the necessity of assuming the mag- 

 nets to be placed end on, an arrangement 

 that is impossible if the magnetic fields are 

 of electric origin. 



In speaking of Ritz's theory, Zeeman^" 

 says : ' ' Though there is something artificial 

 about this explanation, it is the best we 

 have at the present moment." 



9. "Within the past year or two Oxley^^ 

 has shown that the change of magnetic sus- 

 ceptibility on crystallization of some 40 

 diamagnetic substances examined can be 

 satisfactorily explained on the assumption 

 of molecular magnetic fields of the order 

 of 10' gauss. He says in part : 



1. The change of susceptibility observed on crys- 

 tallization demands a local molecular field of this 

 order of intensity [10' gauss]. 



2. The natural double refraction of a crystal- 

 line substance as compared with the artificial 

 double refraction which can be induced in a liquid 

 by the strongest magnetic field at our disposal is 

 consistent with the value of the local molecular 

 field implied by (1) for diamagnetic crystalline 

 media. 



10 "Magneto-optics," p. 182, 1913. 



11 Phil. Trans. Boy. Soc, 215, p. 95, 1915. 



