in the Motion of the Magnetic Field. 315 



tization of matter as a purely kinetic process, and to explain 

 all magnetic phenomena — such as polarity of paramagnetic 

 and diamagnetic bodies, magnecrystallic force, hysteresis — as 

 simple mechanical consequences of the participation of matter 

 in the motion of aether which takes place in magnetic induc- 

 tion tubes? Of this we have no positive proof; but this 

 hypothesis is attractive by reason of its simplicity, and at the 

 same time does not contain anything improbable. To explain 

 all phenomena by means of the properties of matter in motion 

 and to deduce all laws from the laws of kinetic energy — 

 has not this always been what natural philosophy has striven 

 to achieve ? The idea of connecting the motion of matter and 

 aether dynamically is also not novel : in this way only was 

 Helmholtz enabled to explain the phenomenon of anomalous 

 dispersion. Magnetism also possesses its own anomalous dis- 

 persion : it is paramagnetic polarity of some bodies in relation 

 to diamagnetic polarity of others. And in reality, as we shall 

 see further on, the paramagnetic refraction of lines of mag- 

 netic force — to use Faraday's deep and expressive language — 

 is just the same mechanical consequence of absorption of 

 energy as is the anomalous dispersion of lines of the light- 

 radiation. Diamagnetism of matter, as is known, is explained 

 very easily by admitting the existence of molecular electric 

 currents, excited by the surrounding magnetic field and cir- 

 culating freely and without resistance on the surface of the 

 particles of matter. Electromagnetism* shows that the energy 

 of a system of spherical currents, referred to one of these 

 currents, is equal to 



*'-\^.+*-*^**> ■ ■ ■ <*> 



where the integrals are extended over the surface of the 

 current in question, </> is the stream-function, and D. and D, K 

 are the magnetic potentials due to the present current and 

 the surrounding ones respectively. The sign 2 refers to all 

 the surrounding currents. K 



Adapting this formula to the case of molecular spherical 

 currents excited by the magnetic field H, and introducing 

 the intensity of magnetization I instead of the magnetic 

 moment of currents, after the transformation the formula for 

 the energy of molecular currents, referred to unit of volume, 

 will be 



* See Burbury's " On the Induction of Electric Currents in Conducting 

 Shells/' Phil. Trans. 1888, p. 302. 



