BOOKS IN EUROPEAN LANGUAGES
The increase of ferromagnetic moment is appreciated by observing the intensity of the external field. Its maximum value is generally attained at a certain intensity of the field. According to the modern theory of ferromagnetism, the electron spins are considered to take their direction within the field when the intensity of the field is over a definite value. Therefore the maximum value of the moment should be, by this theory, the mean value of atomic moments multiplied by the total number of atoms of the metal under consideration. Since many phenomena are still unexplained, however, the modern theory is not complete. However, it has its significance as it stands. The ferromagnetic theory is a group theory, but manv important relationships among the groups are omitted froljn modern theory of ferromagnetism. In some respects elementary groups of ferromagnetic metal can be considered independently, but in some other cases, connections among groups plav an important part. For example, in an external field of weak intensity the magnetisation of a ferromagnetic metal appears first at one end of the metal and then proceeds with a certain velocity to the other end of metal.*
The form and r\n i ; ..| . gr.iup and the position of a group to its adjacent groups -:,".i;!d le sufficiently treated in the complete theory of magnctisuin "n. The true meaning of ferromagnetic moment will be made clear in the following.
L. Tonks und K. J. Sixtus Phys. Kei: 37,