Kum — Electromagnetic Emission Theory of Light. 321 



single ion could be formed. Resonance on the ground of the 

 continuous ether theory does not account for ionization. 

 That a considerable amount of work is also required to drag an 

 electron out of a metal follows from a recent investigation of 

 the spark discharge by W. W. Williams, who found no spark 

 in a distance of 1,5\ of sodium light when the potential differ- 

 ence was as high as 300 volts. 



§ 6. The intrinsic magnetic field of ferromagnetic substances. 



The hypothesis of the intrinsic or molecular magnetic field 

 due to F. Weiss has thrown a good deal of light on the mag- 

 netic properties of the ferromagnetic substances. The molec- 

 ular Held accounts for the very high value of the magnetiza- 

 tion of iron, nickel and cobalt. There are some discrepancies 

 between theory and experimental results ; for instance, is the 

 law of approach of the intensity of magnetization to saturation 

 not that required by theory, except for cobalt and the variation 

 of the intensity of magnetization with the temperature at very 

 low degrees, does not quite follow the curve given by theory. 



Fig. 3. 



This fact is connected with another result of recent investiga- 

 tion on magnetism, showing that the paramagnetic susceptibil- 

 ity is not in general inversely proportional to the absolute 

 temperature, as was assumed by Curie and Langevin, who 

 considered therefore the moment of an elementary magnet as 

 independent of the temperature. These results make a certain 

 modilication of the theory necessary, but in the main features 



