514 Dr. J. Larmor. The Influence of a 



magnetic force on the motions of oscillating and revolving electrified 

 particles possessing inertia (ions or electrons) in a magnetic field ; 

 and it is thus shown that the broadened edges of the line ought, on 

 Lorentz's view, to be emitting polarised light, viz., plane polarised in 

 directions normal to the lines of force, and circularly polarised in a 

 direction along those lines. 



This prediction has been experimentally verified by Zeeman, and 

 has likewise been confirmed by myself. The flame being looked at 

 from a direction perpendicular to the magnetic field, the light which 

 will be dispersed by the grating to form the extended borders of a 

 line is plane polarised, with its electric oscillations normal to the 

 field's lines of force. 



I hope to have the pleasure of communicating an English version 

 of Professor Zeeman's complete paper to the March number of the 

 * Philosophical Magazine.' 



u The Influence of a Magnetic Field on Radiation Frequency." 

 Communication from Dr. J. LARMOR, F.R.8. Received 

 and read February 11, 1897. 



In the course of the development of a dynamical hypothesis* I 

 have been led to express the interaction between matter and ether 

 as wholly arising from the permanent electrons associated with the 

 matter ; and reference was made to von Helmholtz (1893) and Lorentz 

 (1895) as having followed up similar views. A footnote in Dr. 

 Zeeman's paper has drawn my attention to an earlier memoir of 

 Lorentz (1892), in which it was definitely laid down that the electric 

 and optical influences of matter must be formulated by a modified 

 Weberian theory, in which the moving electrons affect each other, 

 not directly by action at a distance but mediately by transmission 

 across the ether in accordance with the Faraday-Maxwell scheme of 

 electric relations. The development of a physical scheme in which 

 such action can be pictured as possible and real, not merely taken as 

 an unavoidable assumption which must be accepted in spite of the 

 paralogisms which it apparently involves,t was a main topic in the 

 papers above mentioned. 



The experiments of Dr. Zeeman verify deductions drawn by 

 Lorentz from this view. It might, however, be argued that inasmuch 

 as a magnetic field alters the index of refraction of circularly pola- 

 rised light, which depends on the free periods of the material 

 molecules, it must therefore, quite independently of special theory, 



* < Phil. Trans./ 1894, A, pp. 719822; 1895, A, pp. 695743. 

 t H. A. Lorentz, " La Theorie Electromagnetique cle Maxwell, efc ses Applica- 

 tions aux Corps Mouvants," 'Archives Neerlandaises,' 1892. Cf. especially 91. 



