systems of Corpuscles deso'ibir^y CircuJar Orbits. C89 

 the preceding expression, /. e. the mean vahie of 



If the motion of the particle is strongly retarded, the 

 particle ^vill tend to fall in to the centre of the orbit and 



— (y- + c'-) therefore be negative ; thus the mean value of 



the integral will be negative and the mean value of (1) 

 j)ositive. The contribution of this particle to the coefficient 

 of magnetization will therefore be positive, and a collection 

 of such particles will be paramagnetic. 



13. Thus, to take a definite case, suppose the atoms of a 

 substance, like the atoms of radio-active substances, were 

 continually emitting corpuscles; the velocity of projec- 

 tion of the corpuscles under consideration being, however, 

 insufficient to carry them clear of the atom, so that the 

 cor[)Uscles describe orbits round the centre of the atom : 

 then, if the motion of the corpuscles were not accompanied 

 bv dissipation of energy, the corpuscles would not endow the 

 })ody with either magnetic or diamagnetic properties ; if, 

 liowever, the energy of the corpuscles was dissipated during 

 their motion outside the atom, so that they ultimately fell 

 with but little energy into the atom, a system consisting 

 of such atoms would be paramagnetic. If the energy of 

 projection were derived from the internal energy of the 

 atom, there would thus be a continual transference of energy 

 from the atom to the surrounding systems ; this would tend 

 to raise the temperature of the system. I am not aware that 

 any experiments have been made to find whether the tempe- 

 rature in the middle of a mass of a magnetic substance like 

 iron whose surface is kept at a constant temperature differs 

 from the temperature inside a mass of a non-magnetic sub- 

 stance like brass whose surface is Isept at the same tempe- 

 rature. I hope, however, soon to be able to test this point. 



14. The origin of the difference betw^een the effects produced 

 by charged particles describing free orbits, and those produced 

 by constant electric currents describing circular circuits, as in 

 Ampere's theory of magnetism, is that in the case of the 

 particles describing their orbits we get, in addition to the effects 

 due to the constant electric currents, effects of the same 

 character as those due to the induction of currents in conductors 

 from the variation of the magnetic field ; these induced 

 currents tend to make the body diamagnetic, while the 

 Amperean currents tend to make it magnetic : in the case of 



