154 PHYSICS OF THE ELECTRON 



entire account of these facts and clears up at the same time the com- 

 plex question of magnetic energy. 



I shall give here only the principal results of this work which will, 

 be published in full elsewhere. 



(51) Molecular Currents. An electrified particle of charge e mov- 

 ing with a velocity v is equivalent to a current of moment ev. One 

 easily deduces from this that a molecular current made up of an 

 electron which describes in the periodic time t an orbit inclosed by 

 the surface S is equivalent from the point of view of the magnetic 

 field produced to a magnet of magnetic moment M^j- normal to 

 the plane of the orbit. 



There would be a corresponding current for each of the electrons 

 present in a molecule, and the magnetic moment resulting from these 

 would be zero or different from zero, according to the degree of 

 symmetry of the molecular structure. 



(52) Diamagnetism. If on a group of such molecules we superim- 

 pose an external magnetic field, all the molecular currents experience 

 a modification independent of the manner in which the superposition 

 is obtained, whether by the establishment of the field or by motion 

 of the molecule in a preexisting field. The direction of this modi- 

 fication, due to the induction experienced by the molecular currents, 

 corresponds always to diamagnetism, the increase of the magnetic 

 moment being AM" = -^^-S in the case of a circular orbit. H is the 

 component of the magnetic field normal to the plane of the orbit and 

 m the mass of the electron which describes the orbit. 



(53) The Magnetic Energy. When the molecule is supposed im- 

 movable, the work necessary for the modification of the molecular 

 currents is furnished by the electric field produced, according to the 

 equations of Hertz, during the establishment of the magnetic field. 



In the opposite case, where the modification is due to the motion 

 of the molecules, the work is furnished to the molecular currents by 

 the kinetic energy of the molecule or by the action of neighboring 

 molecules. The diamagnetic modification produced at the moment 

 of the establishment of the field continues in spite of the molecular 

 agitation. 



This modification is manifested in three distinct ways : 



1. If the resulting motion of the molecules is zero, the substance 

 is diamagnetic in the ordinary sense of the word, and the order of 

 magnitude of the experimental diamagnetic constants is in good 

 agreement with the hypothesis of molecular currents circulating 

 in intra-molecular paths. 



This conception leads to the law of independence established by 

 Curie between the diamagnetic constants and the temperature or 

 the physical state. 



